Talk:Paper - Peripheral development of the cranial and spinal nerves in the occipital region of the human embryo (1904)
The Development Of The Ckanial And Spinal Nerves In The Occipital Region Of The Human Embryo
Streeter GL. Peripheral development of the cranial and spinal nerves in the occipital region of the human embryo. (1904) Amer. J Anat. 4: 84-116.
By
George L. Streeter, M. D.
Instructor in Anatomy, Johns Hopkins University. With 4 Plates and 14 Text Figures.
The following paper reports the results of a study of the morphology of the ninth, tenth, eleventh, and twelfth cranial and the upper cervical nerves, together with their ganglia, in a series of human embryos. It includes a description of all the stages in the development of these structures from the time at which they can first be definitely outlined from the surrounding mesodermal tissue up to the time they have reached adult conditions. This work was made possible through the kindness of Prof. 0. Hertwig, Prof. His, and Prof. Mall, who gave the writer access to their valuable embryo collections for the purposes of this study. For this courtesy the writer takes advantage of the present opportunity to express his appreciation. Acknowledgment is also to be made to Prof. Gage, whose Buxton embryo is included in the series studied.
The ultimate histogenesis of the nerve elements, a question which has recently been thoroughly gone over by Harrison, 01, and Bardeen, 03, will not be taken up. In the earliest stage where reconstruction was possible the right and left divisions of the ganglion crest have migrated ventro-laterally along the side of the neural tube, and are about to form secondary attachments to it. Fibroblast formation is at this time well under way, and peripheral fibre paths are beginning to become definite. It is the consideration of the size, form, and relation of these paths and the associated ganglion cell masses, in their different stages of growth, toward which attention has been directed.
The results of this study are tabulated at the end of the paper; but special mention should be made of the eleventh cranial nerve. In tracing out its early history it becomes more than ever apparent that it is absolutely similar and continuous with the tenth or vagus nerve. In the embryo these exist, not as two independent cranial nerves, but rather as parts of a single structure, each part possessing mixed motor and sensory roots with root ganglia derived from tlie same ganglion crest. As the development progresses the cranial end of this complex becomes predominantly sensory and the candal end predominantly motor, and also more spread ont which gives rise to a difference in the appearance of the two portions in the adnlt, and has resulted in their being considered as two independent strnctnrcs.
That such a relation between the tenth and eleventh cranial nerves exists is not a new idea, but was long ago suggested by the work of His, 88, on the human embryo, though this investigator did not work with sufficiently young stages to make the evidence conclusive. The theory has since then been supported by the work of Furhringer, 97, and Lubosch, 99, who believe that phylogenetically the tenth and eleventh nerves cannot be separated. Cliiarugi, 90, however, from the comparative embryology of these structures, concludes that the eleventh is not a part of the tenth, but is a nerve for itself which results from the differentiation of the nucleus of origin of the ventral roots into median and lateral divisions ; the latter rootlets losing their segmental distribution take a new course and depart obliquely through the cranium as an independent nerve. Another view regarding these nerves is offered by Minot, 92. He suggests that a modification may have occurred in the motor fibres of the dorsal roots of the hypoglossus, by which these motor fibres, following the abortion of the ganglia, no longer join the ventral roots of the twelfth, but turn forward to join the vagus thereby forming the tnmk of the accessory nerve. Since the work of His, 88, and Mall, 91, on the human embryo, further details in the development of the tenth and eleventh nerves in other mammals have been supplied in the well known papers of Froriep, 83, 85, and 01, and by the work of Robinson, 92, and Letuis, 03. The latter two give us a more accurate description of the so-called ganglionic commissure, than had before existed; although they failed to recognize the full significance of these ganglia and their relation to the precervical ganglia of Froriep.
The comparative morphology of the occipital nerves, particularly with regard to their bearing on the segmental origin of the head, has been the subject of much speculation, ever since Oegenbaur, 72, published his work on the selachian head. The charge may perhaps be justly made that more space in the literature is given to theories and discussions concerning these structures than to actual observations on their comparative and embryological anatomy. This subject will be briefly treated under the heading comparative morphology. It will be emphasized there that the ganglia of the trunks of the ninth and tenth (gang, petrosum and gang, nodosum) are branch io-meric and largely independent of the
George L. Streeter 85
ganglia of the roots. The latter ganglia though not segmental more closely resemble -the spinal ganglia; the attempt however to reduce the cranial nerves to a spinal nerve t3'pe is deprecated. Some sucli liypothesis as was long ago suggested by Balfour, 76, is much easier of application. This investigator supposed the head and trunk to have become differentiated from each other when there was only a mixed motor and sensory posterior root present and no ventral root, as was then supposed to be the case in tlie amphioxus. Since then it has been found (Ransom and Thompson, 86, llatscheck, 92, Dogiel, 03) that the amphioxus and cyclostomes have ventral, purely motor, roots. These do not arise from the cord at the same level with, nor do they join, the dorsal roots. The two might be spoken of as ventral and dorsal nerves. If then Balfour's h3rpothesis were modified to fit with our present knowledge, it could be stated as follows : The head and trunk nerves were differentiated from each other at a time when there existed mixed motor and sensory dorsal roots and pure motor ventral roots. These ventral and dorsal roots did not then arise from the neural tube at corresponding levels, and were independent of each other. In the spinal region of higher vertebrates a modification has occurred, by which the dorsal and ventral roots have become strictly segmeutally arranged, and have joined in pairs, each pair forming a common nerve, which is situated median to the myotome. In the head region the nerves have retained the primitive type; the dorsal roots still contain a good proportion of motor fibres, and are situated beneath the epidermis and outside of the myotomes. They are not segmentally arranged and do not join with the ventral roots to form common nerves, but form a system of separate ventral and dorsal (lateral) nerves.
Material and Methods. — The elements of the peripheral nervous system do not reach a degree of differentiation, wliich is sufficient for reconstruction, until toward the end of the third week. From then changes in the form and relation continue until the tliird month, when the structures have practically reached the condition found in the adult, and development may be considered as completed. The various stages in their growth were thus found to be covered by the embryos listed in the following table (page 86). Their ages have been determined by use of Mall's rule (Mall, 03), ('. c. the age in days equals tlic square root of the product of the length times one hundred.
It was found that the ganglion masses and fibre paths could be satisfactorily identified and traced by means of profile reconstructions. This procedure was made use of with all embryos, with the exception of one at a late stage which was large enough for dissection. The details adopted
86
Development of Occipital Nerves in Human Embryos
in its application consisted in making enlarged drawings of the sections, usually fifty diameters, with a projection apparatus or camera lucida, upon separate sheets of transparent paper. Paraffined wrapping paper is serviceable and inexpensive, better than this, being stronger and more transparent, is the " process " paper, used in Germany as " butter-brodt papier" and in this country in packing tobacco. When the drawings were completed, the sheets were piled so that adjacent sections were accurately fitted over each other. A vertical line for reconstruction was then established by marking upon' each sheet two lines perpendicular to each other, forming a series of crosses which exactly superimposed throughout the entire pile. The individual sections were then plotted off on mm. paper by fitting the crosses to a chosen perpendicular line, the distance between the sections being determined by the thickness of the sections and the enlargement of the drawings in the usual way. Many of these reconstructions are diagrammatically shown as text figures
TABLE OF EMBRYOS STUDIED.
Length.
Ag-e.
Source.
No.
Reconstruction.
4.0 mm.
20 days.
Hertwig Collection.
137
Profile,
one side.
4.3 "
20 '•
Mall
148
both sides.
6.9 "
2(5 "
His
Br3
" "
7.0 "
2(5 "
Mall
2
one side.
7.0 "
26 "
Gage "
Buxton
"
10.0 "
31 "
Mall
114
" "
10.2 "
31 "
His
KO
both sides.
10.0 "
31 "
His
Dl
one side.
13.8 "
37 "
Hertwig *'
67
both sides.
14.0 "
37 "
Mall
144
" " , wax plate
17.5 "
41 "
His
FM
one side.
30.0 "
54 "
Hertwig "
161
"
65.0 "
81 "
Mall
Dissection.
(Figs. 1-12), in which fibre masses are represented by lines and ganglion cell masses by dots. The same enlargement is used in all of these so that the actual increase in size may be readily seen by comparing them.
In order to reproduce the third dimension a clay model was made of a 4.3 mm. embryo, and a wax plate reconstruction of a 14.0 mm. embryo. Drawings of these are reproduced in Plates I and II.
Following the suggestion of Dr. Bardeen much assistance was obtained in studying these structures by making dissections of pig embryos for comparison. It was possible in this way to control the various stages from 8.0 mm. upward. In making such a comparison it was found, however, that the ratio between the length of the pig and the development of its nervous system does not exactly correspond to that of the human. The development of the nervous system of the latter is somewhat more
George L. Streeter , 87
rapid; for example, a 14.0 mm. human embryo shows a stage found in the 18.0 to 20.0 mm. pig embryo. The preparation of these dissections was facilitated by the use of the following method: The entire embryo is mordanted for several hours in a solution of potassium bichromate 2.5 per cent, and glacial acetic acid 10 per cent, after which it is rinsed in water and brought into 80 per cent alcohol. The embryo, after a few minutes dehydration in absolute alcohol, is then attached with a drop of thick celloidin to an isinglass strip, previously coated with thin celloidin. Mica or isinglass is used because it can be easily cut to any desired size. By smoking it, before the celloidin coat, it is possible to write any desired label on it, and the black serves as a good background for the embryo. The whole is then hardened for a short time 80 per cent alcohol, and it is then ready for dissection. In order to hold the embryo during dissection the isinglass strip on which the embryo is mounted is clamped to a stage which is made by fastening a glass slide with balsam to one of the facets of a cut-glass polyhedral paper-weight. Such a stage is steady and can be placed in any desired plane. With the embryo firmly mounted in this way the dissection is made under alcohol with a binocular microscope.
Description of Embryos at Different Stages. Emhryos of About Three Wcel:s.
Hertwig Collection, jSTo. 134 4.0 mm.
Mall Collection, N"o. 148 4.3 mm.
(See Fig:s. 1, 2, 3, and Plate I.)
By the twentieth day the structures have become definite enough in outline to permit of reconstruction. At this stage the ganglion crest of the after-brain and spinal cord has divided longitudinally into right and left halves, each of which has migrated ventro-laterally along the neural tube and forms a flattened cellular band extending caudalwards from the auditory vesicle along the lateral border of the tnbe to its extreme tip.
That part of the crest which corresponds to the spinal cord consists of compactly grouped cells which are so arranged as to present a flattened continuons portion or dorsal bridge, the dorsal border of which is rather smooth and sharply outlined, and shows no connection with the neural tube. There are as yet no dorsal nerve roots. Projecting ventralward from this bridge is a series of rounded segmental clumps of cells which form the primitive spinal ganglia. These end diffusely among the developing fibres of the ventral roots. The ventral border of the ganglionic crest is ill-defined in contrast to tbe dorsal edge of the bridfje of the crest. 7
88 Development of Occipital Nerves in Human Embryos
At this time the fibres of the ventral roots of the spinal nerves are gathered into loose bundles and can be traced a short distance in the
X-Xigang. crest.
bridge.
Fig. 1. Reconstruction of peripheral nerves in three weeks human embryo, 4.0 mm. long, Hertwig collection No. 137. Enlarged 16.7 diams.
gang, crest. XI fibres.
Gang petros.
Fig. 2. Reconstruction of peripheral nerves in three weeks human emhryo, 4.3 mm. long. Mall collection No. 148. Enlarged 16.7 diams.
X x/ gang, crest.
XI f'bres
< peiroSs Gang, nodos.
Fig. 3. Reconstruction of right side of same embryo shown in fig. 2.
mesoderm. Among them are many of the so-called sheath cell nuclei. Owing to the fact that the fibres of the ventral roots run through the
George L. Streeter 89
ventral part of the spinal ganglia it is impossible to determine the presence or absence of fibroblasts belonging to these ganglia.
The first, or most oral, of the spinal ganglia exhibits special characteristics. It is separated from the second ganglion by an enlarged interval, and it is usually smaller and more slender than the other ganglia. In some cases it consists of a very small clump of cells showing no tendency to unite with its ventral root, or it may be absent completely. On the other hand it may be accompanied by additional ganglionic cell-masses representing the occipital ganglia, found by Froriep, 82, to be constant in the sheep. In one case (Fig. 2) the ganglion is divided ventrally into two clumps of equal size, corresponding to a likewise divided ventral Toot. The more oral of these two may therefore be considered as a persistent occipital nerve and ganglion.
That part of the ganglion crest which is situated lateral to the afterbrain differs from the spinal portion of the crest in that it consists of more loosely arranged cells, and as a whole it is flatter and presents an irregularly triangular profile, which at this period does not exhibit a segmental character. That part of it adjacent to the auditory vesicle, and which represents the anlage of the ganglion of the root of the glossopharyngeal nerve, is in most cases completely separated from the rest of the crest. It is continued ventralward into the third branchial arch by a looser zone of cells which connects it, just dorsal and caudal to the second gill cleft, with a rounded compact clump of cells forming the future ganglion petrosum. In a similar manner the ganglionic crest of the vagus at its oral end is continuous by means of an ill-defined zone of cells with the anlage of the ganglion nodosum. This ganglion, as' can be seen in Figs. 1, 2, 3, and Plate I, is larger than the ganglion petrosum. It is somewhat spindle-shaped, and owing to the branchial arches it takes a caudal direction ending diffusely beyond the fourth arch. Directly over it lies a patch of thickened epidermis and is apparently adherent to it. A careful search was made here and in the ganglion petrosum for evidence of interchange of cells between the ganglia and the epidermis without success. That these ganglia are not simply ventral projections of the ganglion crest is in a degree indicated by the zone of less welldefined tissue, which at this stage separates them from the crest proper.
In the ganglion crest, in addition to the cellular elements, there are a few fibres found at the junction of the crest with the neural tube, thus completing the anlages of the glosso-pharyngeal and vagus nerves. A greater fibre development is found in the caudal part of the ganglion crest of the vagus, where inclosed among the cells, as in a sleeve, is found a well-defined bundle of fibres representing the accessory nerve. This
90 Develoi)mLMit of Occipital Nerves in Human Embryos
bundle makes its appearance at the level of the fourth, fifth, or sixth cervical segment. It consists of fibres which are contributed to it at irregular intervals by the dorso-lateral border of the neural tube. In■ creasing in size it extends forward, running mesially to the ganglion crest until it reaches the crest of the vagus where the cells of the crest form a sheath for it. The tip of this nerve reaches to the dorsal border of the column of cells which extends from the crest to the anlage of the ganglion nodosum.
The hypoglossal nerve is represented by a row of four or five rootlets, which are in a direct line with those forming the ventral roots of the cervical nerves, and resemble them with the exception that they successively taper off smaller as they become more oral. At this stage they have not grown far enough out for coming together to form a common trunk. The rootlets are bundled together in three divisions, between which are situated the first two occipital myotomes. The third myotome lies between the last division of the hypoglossal and the first cervical nerve.
On looldng back at these embryos of the third week, an important feature is observed in the fact that the main motor elements are indicated at this time by the presence of fibres. We find a few fibres in the roots of the ninth and tenth nerves; the trunk of the eleventh is definitely laid down, also the roots of the twelfth and the ventral roots of the spinal nerves. The sensory elements, however, are only indicated by the celhilar masses of the ganglion crest.
Embryos of About Four ^Yecli's.
His Collection, Embryo Br3 6.9 mm.
Mall Collection, ^o. 2 7.0 mm.
Gage Collection, Buxton Emljryo 7.0 mm.
(See Figs. 4, 5 and fi.)
In this group of embryos the ganglionic crest is increased in size, but aside from a disproportionate increase in fibre elements, it presents much the same appearance as seen in embryos of three weeks. The flattened dorsal border of the spinal crest still forms a continuous bridge along the tops of the primitive ganglia. Cropping out along this bridge numerous fibroblasts are seen attaching themselves to the spinal cord. These are the primitive dorsal nerve roots. Attention is directed to tlie later and slower development of these as compared with the ventral roots. Aside from that seen in the dorsal bridge the ganglia show as yet little or no fibre formation. They consist of cells whose round nuclei, scantly sur
Georffc L. Streeter
91
rounded by protoplasm, are compactly clumped together, the whole forming a row of pillow-like bodies whose ventral borders are lost among the fibres of the ventral roots.- It was not possible to determine as to whether or not the ventral borders of the ganglia are involved at this stage in fibroblast formation, and contribute fibres to the nerve root, because of
Opthal div
Fig. 4. Reconstruction of peripheral nerves in four weeks human embryo, 6.9 mm. long. His collection Embryo Br3. Enlarged 16.7 diams.
the difiiculty of differentiating them from the mesodermal sheath cells of the ventral roots.
The fibres of the spinal nerve roots form compact bundles which branch, as they extend forward, and form intersegmental anastomoses. The profuse anastomosis of the nerve roots from the fourth cervical to the first dorsal segment marks a primitive brachial plexus. (See Fig. 4.)
92
Development of Occipital Nerves in Human Embryos
The roots of the e-audal cud of the cord are somewhat tardier in their development, and at this stage the lumbar ploxus is only slightly indicated.
Opthal. div.
Sup rndLxdiv. masticatorius.
Jnf max.div.
"Oar\g. nodos. Fig. 5. Reconstruction of right side of same embryo shown in tig. 4.
Sens. organ on gang.petros. Fig. 6. Reconstruction of peripheral nerves in four weeks human embryo, 7.0 mm. long, MaU collection No. 2. Enlarged 18.7 diams.
On the right side of Embryo Br3 (see Fig. 5), and on the left side of the Buxton Embryo, the first cervical ganglion consists of but a small clump of cells showing no connection with the ventral root, which root,
George L. Streeter 93
however, is well developed. Cases of this kind have in the adult the appearance of entire absence of this ganglion, a point which will be taken np later.
The caudal portion of the ganglion crest of the after-brain is longer and more slender than in the previous stage. The accessory nerve is still ensheathed by the cells of the crest. As it extends forward it turns the curve on the back of the trunk of the vagus, and then freeing itself from the vagus it extends a short distance lateralward and ends abruptly in a mass of condensed mesoderm, the anlage of the m. sterno-cleido-mastoideus. The oral end of the ganglion crest of the vagus is connected with the ganglion nodosum (it will be observed that this ganglion is not considered as simply a part of the vagus crest, which is because of the apparent independence of the two seen in three week embryos) by a compact mass of cells, among which are found some fibres. From the ganglion nodosum there arise two distinct fibre bundles, ventrally the superior laryngeal, and ventro-caudally the main trunk of the vagus, around which winds the hypoglossal nerve.
The rootlets of the hypoglossal nerve unite and form a stem, as in the adult, which seems to be joined by fibres from the first and second cervical nerves at the point where it bends upward to reach the anlage of the tongue. • The descending branch of the hypoglossal can be identified on the right side of Embryo Br3 as a short bud at the point where the nerve crosses the main trunk of the vagus. Thus the descendens hypoglossi develops in this case simultaneously with the appearance of anastomoses between that nerve and the upper cervical nerves.
The root of the glosso-pharyngeal nerve is definitely connected with the ganglion petrosum by a fibro-cellular mass. Ventral to the ganglion the trunk of the nerve is represented by a fibre strand extending into the third branchial arch. In Fig. 6 is represented the area on both the petrosal and nodosal ganglia which still remains attached to the overlying thickened epidermis. In Embryo Br3, on both sides of the embryo, the ganglia nodosum and petrosum appear to fuse.
On review of this group it is seen that at the end of the fourth week the ganglion crest is not yet entirely differentiated. We find laid out, however, the roots, the trunks, and the ganglia of the trunks of the ninth and tenth cranial nerves. Further, all the elements of the eleventh and twelfth nerves are present, and the dorsal and ventral roots and the plexuses of the spinal nerves.
Vagus root gang, (jugular)
Accessory root gang.
IX root gang.
Gang, nodes N laryg sup.
Froriep.
Rad. dors.
— In ter- g^nq. bridge..
Fio. 7. Reconstruction of peripheral nerves in thirty-one days human embryo, 10.3 mm. long, His collection Embryo KO. Enlarged 16.7 diams.
Vagus root gang. Accessory root gang
Rad dors.
^ root gang.
Vag
R descenders.
Fig. 8. Eeconstruction of right side of same cnibrj o shown in fig.
Gcortre L. Strccter
95
Embryos of Ahout Tliirti/ Days.
Mall Collection, No. 114 10.0 mm.
His Collection, Embryo Dl 10.0 mm.
His Collection, Embryo KO 10.3 mm.
(See Fig-s. T, 8, 9 aiul 14.)
On coming to embryos 1.0 cm. long the final steps in the transformation of the occipital ganglion crest into cranial nerve rootlets and their ganglia may be seen. When Figs. 7 and 8 are compared with Fig. 4, a considerable increase in the actual mass of cells is observed in this region, and also a marked growth of the fibre elements. As this fibre formation
ory va9u5
Rad . dors.
Interganglionic ■bridge
Fig. 9. Heconstruction of peripheral nerves in thirty-one days human embryo, 10.0 ram. long. His collection Embryo Dl. ^Enlarged lfl.7 diams.
96
Development of Occipital Nerves in Human Embryos
continues the cell masses become broken up and separated into ganglionic clumps. Instead of the uniform cellular crest seen in the occipital region in Fig. 4 we find in Fig. 9 a chain of ganglia lying among the rootlets of the ninth, tenth, and eleventh nerves. Just cephalad to the first cervical ganglion, in Fig. 7, is a cell mass which may be regarded, either as a fragment which has become separated off from the first cervical ganglion, or what is more likely a persistent occipital ganglion (precervical ganglion), such as is found by Froriep, 82, in the sheep.
J^ccessory root gang.
X root gang.
Fig. 10. Reconstruction of peripheral nerves in five weeks human embryo, 13.8 mm. long, Hertwig collection No. 67. Enlarged 16.7 diams.
Embryos of Five to Seven Weeks.
Hertwig Collection, No. 67 13.8 mm.
Mall Collection, No. 14-L 14.0 mm.
His Collection, Embryo FM 17.5 mm.
(See Figs. 10, 11, 13 and Plate If.)
At the end of the fifth week the ganglion crest is completely resolved into a series of more or less segmental cell masses. The dorsal ridge, which formed an intersegmental bridge across the tops of the spinal ganglia, has disappeared. Simultaneously with the disappearance of this
Georoc L. Streeter
97
structure occurs the outgrowth of the central rootlets of the ganglia. On comparing Figs. 1, 9, and 11 one gets the impression of an actual conversion of the dorsal bridge into the ganglion rootlets. In Fig. 10 the dorsal rootlets have attained a considerable length, and show a tendency toward anastomosis.
Vagus root gang
' Accessor y root gang.
IX root gang
N tymp Gang, petros
Gang, nodes. N-lary(^. sup.
XII \^ith r descend.
Sympathetic.
Vagus
Froriep
Fig. 11. Reconstruction of peripheral nerves in Ave weeks human embr3'o, 14.0 mm. lonfr. Mall collection No. 144. Enlarged 16.7 diams. This drawing- is reversed right tor left.
The eleventh cranial nerve lies median to the dorsal rootlets, and is attached at irregular intervals to the spinal cord, just ventral to their attachments to the cord. It may run either mcsially or laterally to the rootlets of the first spinal ganglion, and is usually adherent to the ganglion itself. Cell masses are found on the trunk of the nerve in this
98 Development of Occipital Nerves in Human Embryos
region, as thoiigh fragments of this ganglion. The close relation between the first cervical ganglion and this nerve serves to explain the conditions found in the adult. Along the more cranial portion of the nerve there is a row of ganglia, the accessory root ganglia, which become successively larger as we go forward, and which form a series with the ganglion jugulare of the vagus. The number of these accessory ganglia is usually three or four principal masses, and in addition there are several smaller clumps scattered among the rootlets. In a series of pig dissections at the corresponding age it was not possible to determine a true segmental order in their formation, and there was no correspondence between these ganglia and the number of the hypoglossal roots, and they show no connection with them. Thus they are not to be confused with the occipital ganglia of Froriep. The fibre elements of the accessory nerve fuse with those of the vagus. The occurrence of an actual interchange of fibres between them cannot, however, be determined. Leaving the vagus at the ganglion nodosum the accessory can be traced through the m. sternocleido-mastoideus to the m. trapezius.
The relations of the roots, ganglia, and trunks of the ninth and tenth nerves were seen in the previous stage (Figs. 7, 8, and 9) to have taken on the adult type. In Figs. 11 and 12 the resemblance to the adult conditions is more complete owing to the relative increase of fibre elements. The glosso-pharyngeal nerve arises by several compactly bundled rootlets attached to the neural tube median and caudal to the cartilagenous mass in which the internal ear is embedded. Among these rootlets is the ganglion mass which forms the ganglion of the root or Ehrenritter's ganglion. Beyond this begins the trunk of the nerve, on wdiich is found a second ganglion, the ganglion of the trunk. It is to be remembered that the ganglion of the root and the ganglion of the trunk have developed separately, and have so far remained discrete structures. From the ganglion petrosum is given off ventrally the tympanic branch, or nerve of Jacobson, and caudally the main trunk of the nerve, which hooks inward and forward toward its terminal distribiition. The ninth and tenth nerves lie closely together and there is ample opportunity for anastomosis between them, especially between the ganglia of the trunks. It will be recalled that in a 3^ounger embryo (Fig. 4) these ganglia were apparently continuous.
The vagus presents the same general type as the glosso-pharyngeus; the root and trunk ganglia are larger, and the trunk itself may be traced down into the thorax.
In Fig. 11 the chain of cervical sympathetic ganglia is indicated, and in Fig. 12 is shown their connections with the spinal nerves. The upper
Georcje L. Streetcr
99
portion of this ganglionic cliain fuses with tlie ganglion nodosum, and above this it gives off its branches to tlie carotid plexus.
Vogu5 root gong.
Accessory root gang.
Fror/ep
Sympathetic.
Fig. 13. Reconstruction of peripheral nerves in six weeks human embryo, 17.5 mm. lunjj His collection Embryo FM. Enlarged 16.7 diams.
100 Development of Occipital Nerves in Human Embryos
The principal branches and conininnications of the hypoglossal and cervical nerves may be distinctly traced in embryos of this size. It will be seen that we thus have in this group the completion of the principal features of both the fibre and the cellular elements of the nerves under consideration; but the picture presented by the adult structure varies somewhat from this, owing to a disproportionate growth of some parts over others, and instead of what here appears as a ganglion cell predominance we meet there with a predominance of the fibre elements.
Emhryos of the Second and Third Month.
Hertwig Collection, Xo. 161 30.0 mm.
Mall Collection 65.0 mm.
(See Plate III.)
During the second and third months there is a progressive growth of the fibre elements with a corresponding stretching-out of the nerve trunks and rootlets, which results in a greater separation of the ganglion masses from one another. The further growth of the ganglia is not uniform; while the ganglia of the trunk of the ninth nerve, and of the root and trunk of the tenth, and the spinal ganglia continue in their development, the ninth root ganglion and the root ganglia of the eleventh reach at this time a point of development at which they remain stationary.
In a reconstruction of the left side of the Hertwig embr}-©, No. 161, which is not here reproduced, the noticeable change from the conditions shown in Fig. 12 is in the length and sharper definition of the trunk of -the accessory nerve. On the trunk of this nerve, between the first cervical ganglion and the ganglion jugulare, there are two root ganglia, and as the accessorius trunk joins the vagus there is a third ganglion mass, which, however, is partly fused with the ganglion jugulare. There are also small clumps of cells among the rootlets of the vagus, as well as on some of the central rootlets of the spinal ganglia.
A dissection of this region in an embryo at the end of the third montli is shown in Plate III. There the ganglia of the root of the ninth and the eleventh nerves present very little enlargement. They can be distinguished from the fibre bundles only by a greater opacity, and appear as white nodes in the roots of the respective nerves. The first cervical ganglion is well developed. An arrest in the growth of this ganglion, similar to that in the ganglia just mentioned, might also be expected.
As the nerve fibre growth continues, the last trace of these rudimentary ganglia is lost to the naked eye. In order to determine their ultimate fate a series of sections was made throuo-h the structures of this region in an
George L. Streeter
101
adult specimen. This shows the presence of persistent clumps of normal appearing ganglion cells, situated along the trunk of the eleventh and on the roots of the ninth and tenth nerves. A diagrammatic reconstruction of the series is shown in Fig. 13. In this case the first cervical nerve received a communicating branch from the accessory, but macroscopically no ganglion was present. In the series, however, this ganglion is represented by a circumscribed group of cells on the trunk of the accessory. Among the rootlets in the same region are scattered groups of cells Avhich may have been separated off from it. On going further forward other small ganglion groups are met with, either just beneath the connective tissue sheath of the nerve roots, or among their fibres, and usuallv near
ace essory root ganglia
rtymp
Gang petros
Gang nodosum.
Fig. 13. Diagrammatic reconstruction of ganglion cell masses in peripheral nerves of occipital region in human adult. Compare with Plate IV.
the junction of the roots with the larger trunks. From their position these are considered to be the persistent accessory root ganglia. Although rudimentary in size they are made up of cells which have all the appearances of functionating ganglion cells. It is possible that it is these that provide the sensory fibres for that branch of the accessory which joins with fibres from the vagus to form the pharyngeal branch, in some such way as is schematized in Plate IV.
Development of Individual Xerves.
It has been seen, in tracing the development of the ganglionic crest of the after-brain, that the ninth nerve stands apart from the more caudal nerves and develops independently, and apparently uninfiuenced by them. The tenth and eleventh, in contrast, are parts of a single complex, and cannot be taken up as individual structures without adopting a sepa
103 Developnieiit of Occipital Nerves in Human Embryos
ration that would be artificial; they will therefore be described together. The hypoglossus and the cervical nerves, where a close relation also exists, will be likewise treated.
The Glosso-Pharyngeal Nerve from the beginning possesses the characteristics of a mixed nerve. In embryos 4.0 mm. long (Fig. 1) it consists of a small clump of ganglionic cells, which can be distinguished in the mesenchyma attached to the neural tube just caudal to the otic vesicle and extending toward the third branchial arch. This group of cells represents the anlage of the ganglion of the root, or Ehrenritter's ganglion. Among these cells are a few fibroblastic processes, which do not belong to them, but arise from cells of the neural tube in the dorsal part of the ventral zone of His, and form the motor elements of the root. The character of this anlage resembles that of the vagus; and may be regarded as a part of the ganglion crest of the after-brain, though it is not continuous with the vagal portion of it. It is evident that this ganglion is not a part which has become separated off from the ganglion petrosum as described by Henle, and others (see Thane, 95), but is an independent structure. Its inconstancy is to be explained by its further development. It reaches a size early in the embryo at which it ceases to further develop, in some embryos earlier than others. The fibre elements, however, continue to grow, and finally overgrow the ganglion and thus cause it to be apparently absent. A similar occurrence will be seen in case of the root ganglia of the accessory nerve.
Ventral to this group of cells is a somewhat larger clump of cells, the primitive ganglion petrosum, which is situated directly beneath the epidermis at the caudal and dorsal margin of the second gill cleft (see Figs. 1, 2, and 3). At this time it is separated from the rest of the anlage of the ninth by a looser zone of cells, and this gives it the appearance of having developed in situ, rather than of being a subdivision or bud from the rest of the anlage. It is true that the same appearance might arise from a migration of cells from the latter followed by a proliferation of them at this point. The position of the ganglion petrosum here and in older embryos (Figs. 4, 5, and 6) indicates a close relationship between it and the branchial arches, and the same is likewise true of the ganglion nodosum. In this respect the anlages of the ganglia of the trunks differ from the ganglionic crest proper, or anlage of the root ganglia, which is well removed from the branchial arches and does not show any trace of branchio-meric arrangement. This suggests a difference in origin to exist for the two kinds of ganglia. Another point of difference between the ganglia of the roots and the ganglia of the trunks of these nerves is the
George L. Streeter 103
fusion of the latter with au overlying patch of thickened epidermis, and an apparent absence of such a fusion in case of the ganglia of the roots.
The relation existing between the ganglia of the seventh, ninth, and tenth nerves and the overlying epidermis has-been described in mammals by Froriep, 85, and it is regarded by him as the anlage of rudiments of the phylogenetically lost branchial sense organs of Beard, 85, and van Wijhe, 82. In elasmobranchs Froriep, 91, describes later a double "ne of fusion between ganglia and epidermis, forming the lateral and epibranchial sense organs, which may perhaps be considered as comparable to the ganglia of the roots and ganglia of the trunks. In mammals, however, he had found only a single line of epidermal fusion, that existing over the ganglia of the trunks. In our series of embryos the ganglia of the roots do not seem to take part in the formation of epidermal sense organs, and show no sign of fusion. The condition here resembles that' described by Fronep, 85, in his earlier paper. The adherence between the epidermis and the ganglion petrosum and nodosum is indicated in Fig. 6. It is found in all the human embryos studied from 4.5 to 7.0 mm., after which it disappears. This is a somewhat earlier and briefer period than given by Froriep for other mammals. No indication of interchange of cells between ganglia and epidermis could be made out.
The ganglion petrosum in embryos 7.0 mm. long has become connected with the ganglion of the root by a definite strand of mixed fibres and cells, the fibre elements more and more predominating as the embryo becomes older. At the same time a tapering bundle of fibres sprouts from the distal end of the ganglion petrosum, and forms the main trunk of the nerve, the ramus lingualis, and supplies the third arch. Another branch appears in 14.0 mm. embryos, the ramus tympanicus, and extends forward into the second arch. The ganglion thus gives- off a branch both oral and caudal to the second gill cleft, and this completes the glossopharyngeus as a typical visceral arch nerve. This was pointed out in mammals by Froriep, 85, who regards the r. lingualis as the post-trematic and the r. tympanicus as the pre-trematic branch.
Communications exist between the ganglion petrosum and the ganglion nodosum in an embryo of 7.0 mm. (Figs. 4 and 5), where they seem almost as a continuous structure; in other embryos of this stage, and younger, they are completely separated. Later (Figs. 7, 8, and 9), following the relative change in position of the adjacent parts which succeeds their unequal growth, these structures are gradually brought close together, and secondary communications are established between them.
104 Development of Occipital Nerves in Iluiuau Embryos
The Vagus Complex includes both the vagus and accessory divisions, the tenth and eleventh cranial nerves, which develop practically as a single structure; though the complex is more spread out than the trigeminal, yet the relation of the accessory to the vagus is embryologically much the counterpart of that of the motor root of tlie trigeminus to the rest of that nerve. To speak of the two divisions as individual cranial nerves is misleading; perhaps a new terminology should be introduced, which would express more exactly their comparative and embryological relations. Onodi, 02, has suggested the entire removal of the name accessorius as an independent cranial nerve, but does not himself attempt to carry it out. Eventually such a radical attack upon the nomenclature may prove advisable; in this paper, however, whenever it is necessary to distinguish between the different parts of the vagus complex, the original usuage will be retained which is based on the gross anatomy of adult specimens: the term "vagus nerve" will be applied to that portion of the complex represented by the ganglion jugulare with its rootlets, and the peripheral nerve trunk extending from this on which is found the ganglion nodosum; the term "accessory or eleventh cranial nerve," no distinction being made between vagal and spinal portions, will refer to the remainder of the complex situated caudal to this, and includes ganglionated rootlets and the large motor trunk extending peripherally to the sterno-cleido-mastoid and trapezius muscles. In their development it will be seen that both divisions contain motor elements, which spring in a continuous line from the lateral border of the neural tube as far down as the third or fourth cervical segment, and sensory elements which are developed from the cells of the ganglion crest. Later, following its further growth, the oral or vagus division of the complex becomes predominantly sensory, and the caudal or accessory division predominantly motor.
The ganglion crest of the after-brain is apparently directly continuous with that of the spinal cord, and extends from the first or second cervical ganglion to the otic vesicle, an interruption indicating the division between the ninth and tenth nerves. We agree with Dohrn, 01, who describes the vagus crest as forming a unit wath the spinal crest, rather than with Froriep, 01, who distinguishes between a ganglion crest of the head and one of the trunk, and states that they do not simply go over into one another, but overlap and run along adjacent to each other, each ending for itself. Evidence of such an overlapping could not be made out.
An embryo of 4.0 mm. represents the youngest stage at which the crest was sufficientlv differentiated from the mesoderm for accurate recon
George L. Streetcr 105
striicticm. The slia])^ ol' tlie civst at this time is' ri'iircsi'iiled in Figs. 1, 2, 3, and Plate I. In the iigures the presence of dcvel()|)ing nerve fibres are diagranimatically shown among the cells of the crest. Small bundles of these fibres spring at irregular intervals from the lateral angle of the neural tube and enter the crest. In the caudal two-thirds these fibres join to form a definite strand, wliich is the primitive trunk of the accessory nerve. This trunk reaches down into the region of the spinal ganglion crest to the level of the third or fourth cervical segment. The fibres do not, however, enter this crest, but run along median to it as far as the first cervical, when they enter the vagus crest as though into a sleeve. In regard to the first cervical a variability is shown, the trunk may run median, lateral, or through it. Forward, in a line with these fibres of the accessory trunk, are found a few others forming small scattered bundles at the head of the crest. That the fibres which are present at this stage are motor may be inferred from three facts : firstly, they spring from the lateral horn region of the neural tube; secondly, there is at this time no apparent fibroblast development in tlie cells of the ganglion crest; and thirdly, some of them can be followed in their further development until they become known motor elements, as in the case of the main trunk of the accessorius, and as in the spinal cord where the ventral roots at this time are well laid out, though there is as yet no trace of dorsal roots.
Ventral to the head of the vagus crest, and partially separated from it by a looser zone of cells, is found a second ganglionic mass, the primitive ganglion nodosum, the relation between Avhich and the crest repeats the condition found betw'een the ganglion of the root and the ganglion of the trunk of the glosso-pharyngeus, evidence of independence being here equally strong. As was there pointed out, the ganglion nodosum is closely associated with the development of the more caudal branchial arches. The patch of thickened epidermis over the ganglion, as in Fig. 6, represents an epibranchial sense organ. A complete segmentation of the ganglion nodosum, which might be expected in considering this anlage as the morphological equivalent of a series of gill cleft ganglia, is not found, though the cells show at first a loose irregular grouping, which represents perhaps a branchio-meric tendency. The laryngeal branch of this ganglion is present in 7.0 mm. embryos, and forms the principal nerve to the fourth branchial arch. The main vagus trunk is differentiated at about the same time and is seen sprouting out from the distal end of the ganglion.
At the end of the first month (Figs. 7, 8, and 9) the cellular column between the ganglion nodosum and the ganglion crest is converted into a fibrous trunk. At tliis time the ganglion crest, besides an increase in
106 Dcvolopmcnt of Oeoipitiil Norvos in TTiiinan l^ml)rvos
size, is niodided in ronii by llii^ (IcvcIopnKMit ol' numerous rootlets attaching it to tlie neural tube, and by an irregular clumping together of the cells of the crest, forming ganglion masses along the main trunk of the accessorius, which now lies at the ventral border of the crest. Tlie rootlets which are developed at this time are in part sensory, as is evidenced by comparison with the dorsal spinal roots. The division of the crest into ganglion masses is accompanied by a rapid development of fibres between its cells, and it is probable that the growth of these fibres is the cause which spreads the cell masses apart into separate clumps. Such a separation into clumps radically differs from true segmentation, the latter does not seem to occur here. As the fibre growth continues the ganglion masses become more and more separated, and finally the crest becomes completely converted into a series of discrete ganglia (Figs. 10 and 11). The most oral one is the largest and forms the vagus root ganglion, the ganglion jugulare. Caudal to this, successively diminishing in size, is a chain of three or four accessory root ganglia, which extend backward along the accessory trunk until they meet the cervical ganglion series. In the vagus complex the ganglia diminish in size in the caudal direction, while in the spinal series the reduct?on in size is in the oral direction ; this fact enables one to distinguish between accessorius root ganglia and precervical (Froriep) ganglia. Those ganglion masses found adherent to the accessorius between the first and second, and the second and third cervical ganglia, as in Figs. 10, 11, and 12, are developed from the spinal crest, and represent nodules derived from the spinal ganglia and which have become separated off. Formed similarly to these, are found isolated masses on tlie rootlets of the • jugular ganglion.
The vagus division of the complex at this stage (embryos of 11.0 mm.) therefore consists of mixed motor and sensory rootlets, the ganglion Jugulare, and the nerve trunk on which is situated the ganglion nodosum, giving off a lar}aigeal branch as well as communicating branches to the ganglion petrosum. The accessory division begins at the third or fourth cervical segment. Its trunk runs median to the dorsal roots, except at the first cervical where it may be lateral. It is attached to the neural tube by mixed rootlets, on which are found a varying number of ganglia. The trunk after an arched course joins the vagus division, but the greater portion of it soon leaves the vagus and extends to the shoulder region and supplies the sterno-cleido-mastoid and trapezius muscles.
The essential features of embryos of the fifth and six week, Figs. 11 and 12, will be observed to be the same as in older embryos and in the adult, Plate III and Fig. 13. The existing difference may be accounted
George L. Streeter 107
for by llic disproportionate growtli of the fibre elements over that of the cellular elements, and of some of the cellular masses over that of others; most of tlie cell masses persist, but some of tliem early reach a point at which they remain stationary, such as the accessorius root ganglia, and sometimes the first cervical. Following the increase in fibre growth they become buried among the rootlets or on the accessorius trunk, and thougli not seen by the naked eye they can be seen on section. Pig. I'o represents a case in which the first cervical ganglion was macroscopically absent, but microscopically it is present as a large clump of normal appearing ganglion cells within the sheath of the accessorius trunk.
Anastomoses between the first cervical and the trunk of the accessory nerve in the adult have excited much interest. Among others they have been studied by Kazzander, 91, and later by Weigner, 01. A stu'dy of Weigner's drawings shows that the accessory nerve of one side has no ^constant relation to the accessory nerve of the other side in the same individual; they bear themselves as independent structures, and his 37 examinations may therefore be considered as 74 individual cases. By re-analyzing Weigner's cases in this manner instructive data on our present subject have been obtained. They show that the relation in the adult of the first cervical to the accessorius is as follows :
19% — First cervical ganglion and dorsal root are present, and do not anastomose w'ith the accessorius.
19% — First cervical ganglion and dorsal root are macroscopically absent.
62%: — Various kinds of anastomosis between the first cervical dorsal root and the accessorius. In many of these cases the ganglion is macroscopically absent.
These anastomoses are doubtless to be explained on embryological grounds. The relative position of the two structures at the beginning of connective tissue formation would determine their permanent relations. If they lie in contact at that time they become permanently adherent. Secondaril}', when the dorsal roots become thus entangled in the accessory trunk, as they are apt to in case of the first cervical, they are dragged along out of their original position by later growth and the consequent relative shifting of all of the structures in that region. Further irregularities in their course may he caused by the accessory which, being laid down earlier than they, would have tlie tendency to guide the impinging dorsal rootlets out of the direct centripetal line to the neural tube, and along its own trunk, either forward or backward. A diagram showing some of these variations is reproduced in Plate IV. In the same diagram is shown the hypothetical course of some of the other fibres of the acces
108 Development of Occipital Nerves in llumaii Embryos
sory. No motor fibres are represented as running from tlie accessory to the larynx, the absence of such fibres having been well established by the work of Onodi, 02, and others, and the clinical observations of Seijfer, 03. Fibres of the accessory doubtless join the trunk of the vagus, but they are omitted here for sake of simplicity.
The Hypoglossal Nerve can first be made out in embryos at the end of the third week, at which time it consists of loose fibre strands which can be traced between the occipital myotomes springing from the ground plate of the neural tube and extending a short distance in the mesenchyma (see Fig. 1). These rootlets are formed in three or four segmental groups and develop in the same line with the ventral roots of the cervical nerves. During the fourth week they grow forward and fuse in a common trunk. At the end of the first month this trunk lias passed around the ganglion nodosum, and curves around the sinus cervicalis mesially and orally to reach the anlage of the floor of the mouth. A week later its principal branches of distribution are indicated.
As the hypoglossus crosses the ganglion nodosum it gives off the ramus descendens, which is first definitely seen in embryos 1.0 cm. long. Mall, 91, and Piper, 00, report its absence in embryos 7.0 mm. and 6.8 mm., respectively. His, 88, pictures a long r. descendens in Br3 (6.9 mm.). In a reconstruction of the same embryo, made since then by the author (see Fig. 4), this is not seen. There is, however, on the opposite side (Fig. 5) a slight indication of a beginning branch. At the time the descendens is developed the opportunity for communication between the hypoglossus and the upper two or three cervical nerves already exists; that is to say, the terminal fibres of the latter end in brush-like tufts in close contact with the former. The amount of interchange of fibres cannot be accurately traced, but it is evident that the character of the descendens is dependent on the nature of the contribution of fibres from the cervical nerves. The course in the development of this cervical anastomosis is as follows (compare Figs. 3, 4, 6, 9, and 11) : The fibres of the hypoglossal and the upper cervical nerves start out perpendicularly from the neural tube, and due to the curve of the latter they come together like spokes in a wheel, and then grow along adjacent to each other into the premuscle tissue of Froriep's schulterzungenstrang ; when the formation of the nerve sheaths begins, adjoining fibres become thereby more or less bound together, and as the individual tongue and hyoid muscles draw apart these nerves are led out into an open plexus, the adult arrangement of which and its variations has been described by Holl, 77. The exact formation of this anastomosis must depend on the position of the fibres at the time the sheaths are formed. This introduces a variabilitv wliich
George L. Streeter 109
might account for the {liffereut arrangements found by Holl. A further source of variation is presented by slight differences in the division line between the rootlets of the hypoglossus and Hie first cervical; the fibres destined for the r. desccndens, for instance, may be either picked up with the more caudal rootlets of the hypoglossal, when there will be little or no communication between the hypoglossal and the first cervical, or on the other hand may be picked up with the first cervical and reach their destination through anastomosis witli the hypoglossal. Thus in embryo No. 144 of the Mall collection (Plate II) on the right side the first cervical contributes no fibres to the hypoglossal and descendens, while ou the left side a large communicating bundle exists between them.
In the early stages the rootlets of the hypoglossal present a close similarity to the ventral roots of the spinal nerves, and now are generally considered as a cranial continuation of them ; the nerve being thus derived from the fusion of three or four segmental spinal nerves, which in the course of phylogenesis have become enclosed in the cranium. In the hypothetical ancestor the segments of the nerve belonged to the trunk, and possessed, in addition to the ventral roots, both dorsal roots and ganglia, the latter becoming subsequently reduced coincidently with the invasion of the vagus group into this region. Strong support to this view was given by Froriep, 83, who in the hoofed animals found persistent dorsal roots and ganglia belonging to one or two of the more caudal divisions of the nerve. Similar precervical ganglion masses and rootlets Avere found in the rabbit, cat, and mouse by Martin, 91, and Robinson, 93. The former describes five hypoglossal ganglia in cat embryos, of which he finds only the most caudal one to persist. He thus apparently includes those that in our series of reconstructions are considered as accessory root ganglia, which we think have a different phylogenetic significance. In the human embryo His. 88, describes an abortive precervical ganglion, and names it after Froriep. Inasmuch as he considers the hypoglossus to belong phylogenetically to the vagus rather than to the spinal nerves, he is inclined to doubt a relation between the Froriep ganglion and the hypoglossus. In our reconstructions a typical ganglion may be seen in Figs. 7 and H. The former is the same embryo pictured by His, and does not essentially differ. On the other side of this embryo. Fig. 8, the first cervical ganglion creeps forward a short distance along the accessorius tract, and thus represents what may be styled as a precervical tendency. An interesting case is shown in Fig. 8, where the first cervical ganglion is divided in two equal parts, each having its own ventral root. With further growth they would have become separated, as the spinal ganglia do, and then we should have in the more oral one
110 Development of Occipital Nerves in Human Embryos
a typical Froriep ganglion with a ventral root that would liave doubtless joined with the hypoglossus fibres. In Fig. 9 a slight indication of a ganglion is present, though it is not labelled in the diagram. In such cases one cannot say whetlier it belongs to the spinal group or to the accessorius root ganglia of the cranial group. These two seem to develop from the same crest, and it could be expected that the oral tendency of the former and the caudal tendency of the latter might cause in some cases a fusing of the two; such an instance is seen in Fig. 12. Where the retrogression of the spinal elements is advanced, the Froriep ganglion is absent, and the first cervical also then shows abortive tendencies. If Fig. 5 is compared with Fig. 7, it will be seen that there the spinal reduction extends an entire segment further caudad ; instead of a rootless Froriep ganglion, as in Fig. 7, there is in Fig. 5 a rootless first cervical ganglion.
It is evident that there is a great irregularity in the degree of reduction of the occipito-spinal dorsal roots and ganglia in different individuals. By comparing individuals of different ages we cannot therefore estimate the retrogression undergone in the development of a single individual; one cannot say, for instance, that because a Froriep ganglion is present in an embryo of 7.0 mm. and is not present in another embryo of 14.0 mm. that it has in the latter case disappeared. It was found in case of the accessory root ganglia that ganglion masses once present persist throughout life, though they may early reach a point beyond which they do not further develop. The same is doubtless true as regards the Froriep ganglion.
Comparative Morphology. In considering the phylogenetic significance of the nerves of the occipital region it becomes apparent that we are here dealing with structures of two different sources; on the one hand, the cranial nerve elements represented by the glosso-pharyngeus, the vagus, and the accessorius — a portion of the vagus, and on the other hand the elements of spinal origin, the upper cervical nerves and the hypoglossus. The literature concerning the comparative anatomy of these structures is voluminous, and particularly their involvement in the various theories proposing a segmental origin of the vertebrate skull. A complete review of this literature and discussion of the morphological bearing of the cranial nerves is given by His. 87, and again later by Bahl. 92. Since then has appeared the important work of Fiirhringrr, 97, supplemented by tlie omhryological investigations of Braus, 99, and Froriep. 02. ]\Iention should also be made of the work done on the accessory ncnwe by Luhosch, 99. The general facts as known may l)o stated as follows:
George L. Streeter 1 1 1
In the lower fishes the cranial and .spinal elements are clearh' separated and their territories do not overlap; a line may be drawn oral to which all the nerves are cranial and caudal to which all are spinal. In the phylogenesis, owing to a caudal encroachment of the skull into the spinal region, the more oral of the spinal nerves become included in the head region and have special foramina of exit. Those that are thus assimilated by the selachii have been styled by Fiirbringer as occipital nerves, and those assimilated in addition later by the holocephali are called occipito-spinal nerves. With this assimilation, however, the spinal and cranial elements are still discretel}^ separated by a transverse line of demarcation. There is no actual overlapping of the two until we come to the sauropsida. Here and in all higher vertebrates, accompanying the conversion of certain vagus gill muscles into the trapezius and sternocleido-mastoideus, the cranial elements (/. e. vagus complex) make a caudal invasion into the spinal region, in such a manner that the accessory portion of the vagus is found wedging itself in between the ventral and dorsal spinal roots mesial to the ganglia, gaining attachments to the cord just ventral to those of the dorsal spinal roots.
In the human embryo the different stages of this invasion cannot be demonstrated. Either the early steps are not repeated in the embryological history of higher types, or it may be, as McMurrich, 03, suggests, that the derivation of such structures cannot be demonstrated ontogenetically because the phylogenetic stages occur while the structures are still in an undifferentiated state. In the embryos studied, as soon as the nerve elements can be distinguished, they have their final relative position, and the accessorius is found extending well down into the cervical region. Its caudal end is indicated hy " E " in Figs. 1, 2, and 3. The vagus-accessory anlage is, in all three instances, about of the same size. Some variation exists in the extent of overlapping ,of the cranial and spinal parts, as is evidenced by the variation in distance between the ganglion jugulare and the first cervical ganglion. It is doubtless a variation of the individual, and is of the same character as the variation occurring in the distance over which the accessory nerve extends into the cervical region of the adult. In Pig. 14 is shown the wedge-like invasion of the cranial nerve elements into the spinal territory. The figure is a diagrammatic profile reconstruction of an embryo one month old. The gill arches, vertebral skeleton and muscular apparatus, and spinal and cranial nervous systems are plotted out wdth view to a comparison of their relative positions. It shows clearly the impossibility of drawing any transverse lino tlirmigli tlio body, m-al to which everything would be cranial, and caudal to which everything would belong to the spinal
112 Development of Occipital Nerves in Human Embryos
system. The behavior of tlic nt'rvons system adds to tlie irregularity in the line of junction between the head and trunk.
As the accessorius wedges itself into the spinal territory there occurs a progressive retrogression of the more oral spinal elements, resulting in the disappearance of the dorsal roots and ganglia of the occipito-spinal nerves, these being the first nerves encountered. The ventral roots of these nerves persist and join to form the hypoglossus, and supply the
Notochord
Occipital rnyof-orries
V^C m yofome.
Cranial nervous 3 y stern in spinal territory.
Ih rr\yoforr\e-.
Nervous System.
Muscular
Skeleia.1
Fig. 14. Diagrammatic reconstruction of one month human embryo, lU.O mm. Ioiik-, Mall collection No. 144. Enlarged 9 diams.
tongue, which in the meantime has been acquired in the floor of the mouth. In some of the domestic animals (rabbit, pig, cow, and sheep) one or two of the more caudal of the occipito-spinal dorsal roots and ganglia persist as was pointed out by Froriep, 82, whose name they have received. In man the most caudal ganglion occasionally persists, but it is usually without any connection with a corresponding ventral root; in one case, however, a Froriep ganglion with ventral root was present, and doubtless would have joined with the hypoglossus as its most caudal root.
George L. Streeter 113
Often the connection between the ventral root ot the first cervical and its ganglion is also missing in man, and the ganglion rudimentary and found only on section. These rudimentary ganglia during embryonic life become adherent to the invading cranial member, the accessory nerve, and though all connection with the ventral root is absent, they still may functionate by sending their fibres forward or backward along the accessorius, in the latter case joining a more caudal nerve. Although the first cervical ganglion, and perhaps a precervical or Froriep's ganglion may thus lie in the tract of the accessorius, it is to be remembered that embryologically they are separate structures, the one cranial and the other spinal. The apparent relation between the two is only due to the fact that in the early stages they lie closely together, and become adherent in this position.
In addition to these occipito-spinal (precervical, hypoglossal, or Froriep's) ganglia, there are found in the human adult other rudimentarj^ ganglia situated along the accessory nerve, which are of cranial origin, and similar to the root ganglion of the vagus. These are the accessory root ganglia; they form, in the six weeks embryo, a series of ganglionic clumps, which extend caudalward from the ganglion jugulare, successively diminishing- in size, along the tract of the accessory nerve attached to its rootlets. A true segmental arrangement of them does not seem to prevail in the human embryo, and the same is true in dissections of pig embryos. The ganglion jugulare continues to develop, but these accessory ganglia early reach a size beyond which they do not further develop. They, however, do not imdergo retrograde metamorphosis, at any rate not completely, for evidence of them may still be found in the human adult.
The root ganglia of the ninth, tenth, and eleventh nerves develop from a ganglion crest which has an appearance and history analogous to that from which the spinal ganglia develop. The ganglia whicli form on the trunks of the vagus and glosso-pharyngeus apparently develop independently from that crest, and they differ from the ganglia of the roots in being branchio-meric, and in possessing definite traces of rudimentary sense organs.
The hypoglossus in contrast to the tenth and eleventh nerves, which show no trace either in rootlets or ganglia that they w^ere ever formed from a series of segmental nerves, presents a distinct segmental grouping of its fibres, as may be seen in Plate I and Fig. 1. This fact, added to its resemblance in its early stages to tbe ventral roots of the cervical nerves in point of origin from the same column of cells, its relation to the myotomes, and the occasional presence of a Froriep ganglion, offer conclusive evidence that this nerve is the equivalent of three or four ventral
114 Development of Occipital Xcrves in Iluniau Embryos
roots of phvlogoneticall)' lost occipito-spinal nerves, which luive become fused into a single trunk.
Conclusions.
1. The tenth and eleventh cranial nerves are parts of the same complex, both possessing mixed motor and sensory rootlets, together with root ganglia derived from the same ganglionic crest.
2. During the progress of development of this vago-accessory complex the cephalic end becomes predominantly sensory, and the caudal end becomes predominantly motor and also more spread out. This produces a difference in the appearance of the two portions which has resulted in their being considered as two independent structures. The cephalic portion forms the vagus or tenth cranial nerve, and the caudal portion the n. accessorius Willisii or eleventh cranial nerve. The old nomenclature is retained, and in so doing the term eleventh cranial nerve is used as synonymous with n. accessorius vagi plus n. accessorius spinalis.
3. The root ganglia of the tenth and eleventh cranial nerves do not present a definite segmental arrangement.
4. The trunk ganglia of the ninth and tenth cranial nerves (gang, petrosum and gang, nodosum) when first identified are not definitely connected with the root ganglia of the same nerves, and they differ from the root ganglia in having an. arrangem.ent segmentally related to the gill arches, and possessing rudimentarv sense organs.
5. The ganglia found on the rootlets of the eleventh cranial nerve are the counterpart of the root ganglion or jugular ganglion of the tenth. They do not reach the high development of the latter, though traces of them persist in the adult. They are to be distinguished from the precervical ganglion of Froriep, whicli represents an extra spinal ganglion.
G. The eleventh cranial nerve extends caudalward into the spinal region to the third or fourth cervical segment, in some cases further ; the extent and variation in the embryo is the same as in the adult. The caudalward invasion of this nerve is phylogenetic, and not ontogenetic.
7. The hypoglossal nerve in young embryos closely resembles the ventral roots of the adjacent cervical nerves, and is segmentally continuous in the same line with them. That a phylogenetic retrogression has removed the dorsal roots, which they seem to have at one time possessed, is evidenced both by the occasional presence of a Froriep ganglion and by cases in which the retrogression has gone still further caudalward, and has removed the dorsal root of the first cervical nerve.
8. The ramus descendens hypoglossi is developed in some cases before the hypoglossus has received any connecting branches from the cervical
George L. Streeter 115
nerves; in other eases sueh eonneetions are formed coincident with or before tlie r. descendens ajipears. A variable rehation exists between the r. descendens and the coinnnmicating cervical brandies.
9. The ventral roots of the spinal nerves are developed earlier than the dorsal roots. Siniilarlv in the cranial nerves those portions generally recognized as motor are dilYerentiated into fibre paths earlier than the sensory elements.
LIST OF REFERENCES.
Balfour. F. M., 76. — On Development of the Spinal Nerves in Elasmobranch
Fishes. Phil. Trans., Vol. CLXVI. Bardeex, C. R., 03. — The Growth and Histogenesis of the Cerebro-Spinal
Nerves in Mammals. Amer. Jour. Anat., Vol. 2. Beard, J., 85.— The System of Branchial Sense Organs and their Associated
Ganglia in Ichthyopsida. Quart. Jour. Micr. Science, Vol. 26. Bral's, H., gg. — Beitrage zur Entwicklung der Muskulatur u. des peripheren
Nervensystems der Selachier. Morph. Jahrbuch, Bd. 27. Chiarugi, G., go. — Le Developpement des Nerfs Vague, Accessoire, Hypoglosse
et Premiers Cervicaux chez les Sauropsides et chez les Mammiferes.
Archiv. Ital. d. Biol., Tome XIII. DoGiEL, A. S., 03. — Das periphere Nervensystem des Amphioxus. Anat. Hefte,
Arbeiten, Bd. 21. DoHRN, A., 01. — Studien zur Urgeschichte des Wirbelthierkbrpers. Mitth'l.
Zool. Station zu Neapel, Bd. XV. Froriep, a., 82. — Ueber ein Ganglion des Hypoglossus etc. Arch. f. Anat. u.
Phys. Anat. Abth.
85. — Ueber Anlagen von Sinnesorganen am Facialis, Glossopharyngeus
und Vagus. Arch. f. Anat. u. Phys. Anat. Abth.
01. — Ueber die Ganglienleisten des Kopfs und des Rumpfes und ihre
Kreuzung in der Occipitalregion. Arch. f. Anat. u. Physiol. Anat. Abth.
02. — Zur Entwickelungsgeschichte des Wirbeltierkopfes. Verhandl.
d. Anat. Gesell. Halle. FiJBBRiNGER, M., 97. — Die Spino-Occipitalen Nerven der Selachier u. Holo cephalen und ihre vergleichende Morphologie. Festschr. f. Gegen baur. Gegenbaur, C., 72. — Kopfskelet der Selachier. Leipzig. Harrison, R. G., oi. — Ueber die Histogenese des peripheren Nervensystems
bei Salmo salar. Arch. f. Mikr. Anat.. Bd. 57. Hatschek, B., 92. — Die Metamerie des Amphioxus und des Ammocoetes.
Weiner Anatomen Kongress, Anat. Anz. Verhandl., Bd. 7. His, W., 87. — Die morphologische Betrachtung der Kopfnerven. Arch. f.
Anat. u. Physiol. Anat. Abth.
88. — Centralen u. peripherischen Nervenbahnen beim menschlichen
Embryo. Abhandl. math.-phys. CI. Kgl. Sachs. Ges. Wiss., Bd. 14. HoLL, M., 77. — Beobachtungen iiber die Anastomosen des Nervushypoglossus. Zeitschr. f. Anat. u. Entw., Bd. 2.
116 Development of Occipital Nerves in Human Eml)rvos
Kazzandek, J., 91. — Ueber den N. access. Willisii und seine Beziehungen zu
den oberen Cervicalnerven. Arch f. Anat. u. Physiol. Anat. Abth. Lewis, F. T., 03. — The Gross Anatomy of a 12. mm. pig. Amer. Jour. Anat.,
Vol. 2. LuBoscii. W., gg. — Vergleichend-anatomische Untersuchimgen iiber den
Ursprung und die Phylogenese des N. accessorius Willisii. Arch. f.
Mikr. Anat. u. Entwick. Bd. 54. Mall, F. P., gi. — A Human Embryo 26 days old. Jour, of Morphol., Vol. 5. 03. — Note on Collection of Human Embryos. Johns Hopkins Hosp.
Bull., Vol. 14. Martin, P., 91. — Die Entwicklung des neunten bis zwolften Kopfnerven bei
der Katze. Anat. Anz., Bd. 6. McMuRRiCH, J. P., 03. — The Phylogeny of the Forearm Flexors. Amer. Jour.
Anat., Vol. 2. MiNOT, C. S., g2.^ — Human Embryology. Wm. Wood & Co., N. Y. Onodi, a., 02. — Der Nervus accessorius und die Kehlkopfinnervation. Arch.
Laryngol. u. Rhinol., Bd. 12. Piper, H., 00. — Ein menschlicher Embryo von 6.8 mm. Nackenlinie. Arch. f.
Anat. u. Physiol. Anat. Abth. Rabl, C, g2. — Ueber die Metamerie des Wirbeltierkopfes. Verhandl. d. Anat.
Gesell. Wien. Ransom and Thompson, 86. — On the Spinal and Visceral Nerves of Cyclo stomata. Zool. Anz., Bd. 9. Robinson, A., g2.-TObservations on Development of Posterior Cranial and
Anterior Spinal Nerves in Mammals. Report British Assoc, for
Advancement of Sci., Edinburgh. Seiffer, 03.- — Die Accessorius-Lahmungen bei Tabes dorsalis. Berlin. Klin.
Wochenschr., 40-41. Thane, G. D., 95. — The Nerves. Quain's Anatomy, Vol. Ill, Part II. VAN WiJHE, 82. — Ueber die Mesodermsegmente u. Entwicklung der Nerven
des Selachierkopfes. Verhandl. koninkl. Akad. Wetenschappen., 22
Deel. Amsterdam. Weigner, K., 01. — Beziehungen des Nervus accessorius zu den proximalen
Spinalnerven. Anat. Hefte, Arbeiten (Merkel-Bonnet) , Bd. 17.
DEVELOPMENT OF THE OCCIPITAL NERVES
GEORGE L. STREETER
PLATE I
Ga7i<^ . hridoe
Canff. petrosinn.
CuDiff. nodosum.
lf\
PROFILE RECONSTRUCTION OF PERIPHERAL NERVES IN THREE WEEKS HUMAN EMBRYO 4.3 MM. LONG, MALL COLLECTION No. 148. ENLARGED ABOUT 25 DIAMETERS THE THIRD DIMENSION FOR THIS DRAWING WAS OBTAINED FROM A CLAY MODEL, AND THE SHADING IN PART COPIED FROM A PIG EMBRYO OF SAME STAGE.
AMERICAN JOURNAL OF ANATOMY— VOL. I\
DEVELOPMENT OF THE OCCIPITAL NERVES
GEORGE L. STREETER
PLATE II
Accessory rod gang;
rS^uL7N%MlT'^^'°' °' PERIPHERAL NERVES ,N OCCIPITAL REGION OF FIVE KS HUMAN EMBRYO, 14.0 MM. LONG, MALL COLLECTION No, 144. ENLARGED ABOUT 25
WEE DIAMETERS.
AMERICAN JOURNAL OF ANATOMY— VOL. rv
DEVELOPMENT OF THE OCCIPITAL NERVES
GEORGE L. STREETER
PLATE III
X root ^ani^lioN .
IX root ganglion .
Corp. qiiadrigeni.
Cerehelluvi.
XI root ganglia .
Os occip. Atlas. \
Axis.
rl . vertchralis.
M. ster HOC Icidoinastoi dens.
DISSECTION OF NERVES IN OCCIPITAL REGION OF THREE MONTHS HUMAN EMBRYO, 65.0 MM. LONG, MALL COLLECTION. ENLARGED 4 DIAMETERS.
AMERICAN JOURNAL OF ANATOMY— VOL. IV
DEVELOPMENT OF THE OCCIPITAL NERVES
GEORGE L. STREETER
PLATE iV
A FUETHEE STUDY OF THE DEVELOPMENT OF THE EXCEETOEY OEGANS IN" BDELLOSTOMA STOUTI
BY
GEO. C. PRICE, Ph. D.,
Associate Professor of Zoology, Iceland Stanford Jr. University.
With 31 Text Figures.
Much of the following work has been done in the Embryological Laborator}^ of the Harvard Medical School, and it gives me great pleasure to here acknowledge m}' many oliligations to the Director, Professor Charles Sedgwick Minot, for his unvarying kindness and helpfulness. I wish also to express my thanks to Professor Oscar Hertwig for his kindness in placing the resources of his laboratory at my disposal during a four months' residence in Berlin.
In a previous paper on this subject ^ the excretory organs were described in three stages, designated as A, B and C. Of these A showed the system in an early though not in the earliest stage of development, B followed quite closely upon A, but between B and C there was a wide gap, the organs in C resembling in many respects those of the adult.
A subsequent study of better material, and of a rather full series, beginning with specimens younger than A and ending with others older than C, has revealed certain errors both of observation and interpretation, and has at the same time brought to light some new and interesting facts. It is the object of the present paper briefly to present these facts and to correct the errors. No attempt will be made to discuss the morphology of the excretory organs of the vertebrates in general.
It may be stated at the beginning that additional observations have abundantly confirmed the main point of the previous paper, namely, that in Bdellostoma the entire excretory system arises as a pronephros, and that from this both the pronephros and mesonephros of the adult are derived.
In the previous work, on account of the difficulty of counting the myotomes in transverse series, especially at the anterior end, recourse
'Price, G. C: Development of the Excretory Organs of a Myxinoid, Bdellostoma stouti. Zool. Jarb., Vol. 10, Anat., 1897.
American .Tori:NAL of Anatomy. — Vol. IV.
lit)"' ExcretoTy Organs in Bdellostoma Stouti
was liad to tlio spinal ganglia for the pnrpose of determining relative positions. It now sooms best to employ the myotomes for this purpose, especially since in the earlier embryos there is an intimate relation between the myotomes and the excretory organs. It has been found that the first spinal ganglion is located between the third and fourth myotomes, so that where trouble is experienced in counting the myotomes, the ganglia may be counted instead, and the necessary calculations made.
The anterior end of the excretory system is more or less rudimentary, and the position of the first tubule is not constant, but varies both in different individuals and on the two sides in the same individual. In a few cases where its position could be accurately determined, and where there w^as no probability of degeneration having taken place, it occurred in segments eleven to thirteen. In one of the specimens previously studied the first tubule occurred in sections passing through the sixth ganglion. But here the preservation is not all that could be desired, and it is possible, though not certain, that this may really be the seventh ganglion, and the tubule might correspond to the myotome just back of this, which would be the tenth. But making all possible allowances, the fact remains that here the first tubule is farther forward than in any other embryo studied.
The position of the posterior end of the segmental duct has been found to vary from about the seventy-ninth to the eighty-second segment, and possibly a larger nmnber of specimens would show still greater variation.
In. general it may be said that in this animal there is a good deal of variation, l:)oth in the embrj^o and in the adult, a fact that should not be lost sight of in attempting to generalize from a small number of individuals.
So far as my knowledge extends Dean ' is the only other person who has published observations on the excretory system in. the embryos of Bdellostoma. From surface views alone he has described a series of segmental structures, about eighty in number, extending from the region of the neck into that of the tail, and present for a comparatively long period of the development. They are described and figured as large and somewhat complicated bodies, each extending outwards from near the spinal ganglion to the distal region of the somite, and it is suggested that they may be tubules of a pronephric nature. In sections of embryos
^ Dean, Bashford: On the Embryology of Bdellostoma stouti. A General Account of Myxinold Development from the Egg and Segmentation to Hatching. Festschrift zum siebenzigsten Geburstag von Carl von Kupffer. .Tena, 1899.
Geo. C. Price
119
of ages corresponding to those in whicli the above structures are figured 1 have been unable to find any such system of tubules, although on ■account of their size it would seem impossible to overlook them if present. In Dean's figure 13-i the parts marked pronephric tubules bear a striking resemblance, even down to the fine details, to the ventral part of the muscle segments as seen in sagittal sections of an embryo of about the same age as the one from which the above figure was taken, and in the sections there is a comparatively large amount of connective tissue between the muscles which corresponds well with the space between the so-called tubules. Moreover, the muscle segments are the only segmental structures that at all correspond in size to the ones in question.
The youngest embryo studied has one hundred and one myotomes on the one side and one hundred and two on the other, a number fully equalling that of the muscle segments in the adult. There are seven or eight pairs of forming gill slits, only five of which could be made out from the surface view.
Fig. 1. — Section through the fifty-second segment of the youngest emhryo studied. a, aorta ; ch, notochord ; g, spinal ganglion ; Im, lateral mesoblast ; my, myotome ; nc, nephrocoel ; nt, nephrotome ; scl, sclerotome. There is an artificial break, shown best on the right of the figure, separating the myotome from the nephrotome and extending into the sclerotome. The sclerotome is seen to be in connection with the myotome, and on the right the lateral mesoblast is continuous with the nephrotome.
In this embryo there are neither excretory tubules nor excretory ducts in the true sense of the word, but there is an extensive system of nephrotomes from which both tubules and ducts are derived. These extend certainly from the thirteenth segment to the seventy-fourth on one side and to the seventy-fifth on the other, and it is possible they may begin even farther forward than the thirteenth. From the anterior end back to the neighborhood of the fiftieth segment they are all practically in the same stage of development, but from here on they become gradually less well developed until, in the last few segments, they appear to be just forming.
An idea of the relations of the nephrotomes to other parts may be had from Fig. 1, which represents a section passing through the fifty
•.'(I
Exei'dorv ()i'i,miis in J'xlcllostoiim St(niii
second segment, and therefore very near the middle of the body region and about five segments back of the middle of the region of the nephrotomes. The mesoblast, which alone interests us, is divided on either side into four parts, the myotome, my, the sclerotome, scl, the neplirotoine, nt, and the lateral mesoblast, Im.
The m3'otome comes into direct contact with the ectoderm, there being no mesenchyme between them, and this is true for all the segments except the first four or five. There is no myocoel, but the centre of the myotome differs from the periphera in being free from nuclei. In the anterior segments muscle fibres are forming. Nothing of this is seen in Fig. 1, although in the section next in front, which passes nearer the middle of the myotome, some of the cells show signs of differentiation, and this is true also in four or five of the segments further back.
Figs. 2-8. — Seven consecutive sections from the middle of one nepbrotome to the middle of the next, nc, the nephroccel shown in Figs. 2 and 8. Fig. 5 represents the place where the two nephrotomes come together.
The sclerotome, which is formed of compact mesoblast, is still connected with the myotome, and its segmental character is further shown in running through the series, by the fact that at regular intervals the tissue here becomes much less compact. In about the last twenty-seven segments the sclerotomes have not yet been formed.
The lateral mesoblast has the appearance of loose mesenchyme, and extends outward from the nephrotome with which it is continuous. (This is shown only on the right in the figure.) In this section there is no indication of a splitting into somatic and splanchnic layers, although, as will appear later, the process has begun farther forward.
The nephrotome lies just below the outer end of the myotome, from which, in this case, it is separated by a narrow, artificial space, caused presumably by the action of reagents. It is sharply marked off from the surrounding tissue by the compactness of its walls, and it contains a lather large cavity, the nephrococl. nc. In running tlirough the series the segmental character of the ncphrocoels is very striking, as may be
Geo. C. Price 121
gatlieved from Fig's. '2 to S, representing a continuous series from the middle of one neplirotome to the middle of the next, but the segmental character of the solid portion of the neplirotome is not so apparent. This is because the nephrotomes in adjoining segments come into direct contact with each other, and some part shows in every section, just as the segmentally arranged myotomes appear in every section. However, the nephrotomc becomes smaller towards the end than it is in the middle, and the point where two nephrotomes come together (Fig. 5) can quite easily be detected by the smaller size of the section and the indistinctness of the outline.
In order to gain an idea of the appearance of a sagittal section through the nephrotomes, camera lucida drawings were made of all the sections in three segments, and from these Fig. 9 was reconstructed on millimeter paper.
The proportions are here fairly accurate, but it was a question whether the nephrotomes should be represented in close contact with one another, or as having a slight space between them. It is possible, though not probable, that an actual fig. 9.-a reconstruction of a
... I J- • 1 . ^ L- -L sagittal section through throe neph Saglttal section might even show continuity rotomes, made on millimeter paper. , , T . , T , nc, uephroctel.
between adjacent nephrotomes.
The posterior end of one nephrotome and the anterior end of the next (Figs. 4 to 6 and Fig. 9) may be looked upon as forming a sort of short, discontinuous rod. This would be more apparent in a frontal than in a sagittal section. This remark is made because later they form an actual rod extending from one nephrotome to the next, and giving rise ultimately to the greater part of the segmental duct between consecutive tubules.
What has been said thus far in regard to the nephrotomes applies to those representing a middle state of development, those toward the anterior end being in some respects more advanced, and those toward the posterior end less advanced. As an example of the latter we may take the one in the sixty-eighth segment, a section through which is represented in Fig. 10. Here the nephrotome is attached to the myotome, although a well marked constriction has appeared between them. There is a very small nephrocoel, but the greater part of the centre of the nephrotome consists of non-nucleated protoplasm which is continuous with the non-nucleated protoplasm of the myotome. There is no distinct boundary between the nephrotome and the sclerotome. On this side the last nine nephrotomes are attached to the myotomes, and a few just in front have somewhat the appearance of having been torn away.
123 Excretory Or<^ans in J'xiolloslom;!, Sioiiii
Of ilic nine that are attached the second, third and sixth have small ncplirococls, while in tlic rest the center is made up of non-nucleated protoplasm. The transition hetwecn the nephrotomes represented in Fig. 1 or Figs. 2 to 8 and the one represented in Fig. 10 is gradual. Toward the posterior end the constriction between the nephrotome and the myotome becomes less pronounced than in Fig. 10. It is possible that if this embryo had been allowed to develop nephrotomes would have appeared still farther back; at least they are found farther l)ack in older embryos.
The only striking difference between the nephrotomes in the anterior region and those represented in Fig. 1 is that in the former the nephrocoels communicate with the splanchnocoel, as may be seen in Fig. 11.
Kkj. 1(». FlO. ] 1.
Fig. 10. — Section tliroush the sixty-eighth sesment slunving a uephrotome connected with the myotome, tliough partly separated from it. my, myotome ; Im, lateral mesoblast ; nc, a very small uepliroca>l ; nt, nephrotome ; scl, sclerotome. The myotome, nephrotome and sclerotome are all continuous with one another, and the lateral mesoblast is continuous with the nephrotome.
Fig. 11.^ — Section showing the nepliroccel, nv, opening into the splanclinoco!], sc. It also shows the way in whicli the splanchnoco?! first appears as small, rounded cavities in the lateral mesoblast. my, the outline of the end of the myotome.
Here the distinction between the nephrococl and splanchnocoel is at once apparent by the difference in the character of tlieir bounding walls. In this region the nephrotomes come into direct contact with the myotomes and in the fifteenth segment on the right side there is actual continuity between the two.
A few words regarding the distribution of the nephrotomes. In segments nine to twelve there are cavities having the shape and position of nephrocccls, but with bounding walls less well marked than is the case with nephrocoels farther back, and it is doubtful whether thoy would give rise to any part of the excretory system. Nevertheless the feeling can hardly be avoided that these are rudimentary nephrotomes. On the right side in segments thirteen to fifty, and on the left in segjnents thirteen to forty-two the neplirotomcs are in direct contact with
Ceo. C. rriec
123
tlio niyolomos, and, in tlie one case above nolc^il, ilici'c is ncluiil coiitiiunty. In segments fifty-onc to sixty-seven on the right, and in fortytlireo to sixty-five on the left, the nephrotomes and myotomes are separated by narrow, artificial spaces. In segments sixty-eight to seventyfive on the right, and in sixty-six lo scventy-l'onr on the loft, tlio nephrotomes are joined to the outer end of the myotome. It seems fair to su2)pose that in earlier stages all the nephrotomes would be found connected with myotomes, but this could be proved only by the examination of a younger embryo.
A brief account of the fornuition of the splanclmocd'! will now be given. This arises in the lateral mesoblast as small rouiuhnl s})aces (Fig. 11) which grow togetlier, and thus form a continuous cavity on either side, and at the same time split the lateral mesoblast into somatic and splanchnic layers. (No reference is here made to the pericardial cavity.) The entire coclom of the right side, both nephroca^ls and splanchnococl, was reconstructed on millimeter paper, and this shows that tlie region of most active formal ion is in segments nine to fifty-three. In segments (ifty-four to iifiyseven it is almost absent, while back of this it is entirely absent. Fig. 13 shows the crelom in three segments, the heavy lines indicating the boundary of the nephrocoels, and the light tliat of the splanchnocoel. No attempt is made to show anything beyond the outline^ of the cavities. It will be observed that the divisions of the splanchnococl communicating with the nephrocoels have a sort of segmental character, and that the cavity in one segment in no case quite communicates with that in the next. Further forwai-d, however, such commu2iications do occur, in one instance the cavities in four consecutive segments being joined together.
In a few cases a splanchnocoelic cavity was found lying just beyoml the nephrococl, but without any communication between them. In others, as in Figs. 13 to 15, the two are seen to be breaking into eacli otlier. This may not be the only way in which the communication between the nephrococl and s])lanchnocncl is established; in some cases (Fig. 1, right side) a splitting seems to l)cgiii at the nc|)liroc(pl and extend oiitwai'd into the lateral mesoblast.
The next embrvo to which attention will be called is between tlie one
ll(). 12. I{('c()ii>l-niil ion of (In- ('(rloiii ill llircc si'jfmciils ol' an (^iiil)c.\() ill which ( li(^ spill iicli nocMi'i is ill Mil (iiirly stiitro of loriiiiitioii, iiiiido (111 iiiilliiiuitor piilicr. 'I'lic iK'iiiiroiMi'l, /((', Is boiiiiilcMi by t lie hon\y line, and th(^ sphiiK.'hnocii'i hy (he liK'lit. NotliiiiK' is shown lioyoiKl tlio outline ol' tiie cavities.
124 ]*l\ci-otory Organs in Bdollostonia Stouti
just described and tlic youngest of stage A, previously studied, but is nearer the latter than the former. It was cut in two in the region of the forty-sixth segment, the anterior part being sectioned sagittally and the posterior part transversely. There are eleven or twelve pairs of gill slits. Mesenchyme is present between the myotomes and the external ectoderm, and the sclerotomes have been converted into very loose mesenchyme, which shows no signs of segmentation. The splanchnocoel is found from about the ninth to the eightieth segment, and through the greater part of its extent is continuous from segment to segment. In the posterior region, however, it is poorly developed, and here sections are occasionally met with in Avhich it is entirely wanting.
The excretory system extends on the one side from the twelfth to the eighty-second segment, and on the other from the eleventh to the eightyfirst. Through the greater part of its extent it is no longer in contact with the myotomes, mesenchyme having grown in hetween, but towards
Figs. 13, 14 and 15. — Thi-ee consecutive sections showing one way in which the
nephi'ocoel, nc, and splanchnoccel, sc, come together. The Section in front of Fig. 13
shows no splanclinoccpl at all, while Fig. 15 is the only section in which there is a communication hetween the two cavities.
the posterior end of the system the ends of the myotomes gradually approach the nephrotomes, until, in about the last ten segments, the two are either in contact or are actually joined together. From the anterior end back to about the twenty-eighth or thirtieth segment the nephrocoels have either disappeared or are disappearing, by being merged with the splanchnoccel. Beyond this they are all in connection with the splanchnocoel, except the very rudimentary ones in the last four segments.
A good idea of the excretory system as found throughout the greater part of its extent in this embryo may be gained by an examination of Fig. 16, representing a sagittal section through segments forty-four and forty-five. Fig. 17, representing a transverse section through the nephrotome in segment forty-seven, and Figs. 18 to 20, three consecutive sections through the segmental duct, back of Fig. 17. The plane of the sagittal section does not quite coincide with the long axis of the body, hence the difference in shape of the nephrocoels in Fig. 16, the left or posterior one being nearer the median line than the right.
Ceo. C. Price
125
The nepliroeiiL'l has increased in size, especially in its dorso-ventral diameter, and the dorsal wall of the nephrotome as seen in transverse section (Fig. 17), is arched, as if being evaginated to form a tubule. As will appear later this is true only in part. A glance at the sagittal section (Fig. 16) proves that we are still dealing with nephrotomes and that a tubule in the strict sense of the word has not yet appeared.
Extending from one nephrotome to the next is a solid rod of cells (Fig. 16, d), a part of the segmental duct. At one point, about half way between the nephrotomes, the duct is sligtly smaller than elsewhere, and here the nuclei are much less numerous. This is brought out still more clearly in the transverse sections (Figs. 18 to 20). Fig. 19 corresponds to the point a- in Fig. 16, and Figs. 18 and 20 are the sections
Fig. 16. — Sagittal section through the the nephrotomes in segments forty-four and forty-five, the one in forty-four being to the right, d, forming segmental duct ; nc, nephrocoels ; x, place where the two nephrotomes have joined together.
Fig. 17.- — Transverse section through the nephrotome in the forty-seventh segment of the same embryo from which Fig. 16 was taken, nc, nephrocoel ; sc, splanchnocoel.
Figs. 18, 19 and 20. — Three consecutive sections through the duct between the nephrotomes in the forty-seventh and forty-eighth segments. Fig. 19 corresponds to the point x in Fig. 16 and represents the place where the ends of two nephrotomes have united.
next on either side. The relation of the duct to the nephrotomes, and a comparison with the younger embryo suggest very strongly that it has been formed from the posterior end of one nephrotome and the anterior end of the next, the point x being the place where the two have united. This point of union is easily made out in almost all of the segments.
The description just given answers in all essential respects for about three-fourths of the segments, or to be exact, for all except four at the posterior end and twelve or fifteen at the anterior end. However, as we approach the posterior end, in the region where in the older embryos the tubules are rudimentary and early disappear, the nephrotomes become quite a little smaller.
120 Excretory Organs in rxlcllnstoma Stouti
In the last four segments the duct is present as a continuous rod, the outlines of which are not quite so distinct as farther forward. At four places, however, situated at perfectly regular intervals, the myotomes approach and are joined to the duct, and here the center of the duct is filled with non-nucleated protaplasm, in which is a small cavity. These can be none other than rudimentary nephrotomes. Whether they would have developed farther cannot be said, but they are interesting as indicating that the entire duct is formed from nephrotomes, for it is not likely the duct would have extended farther back, at least no case has been found where it extends beyond this point, the eighty-second segment. In the previous paper tubules were foimd to within two segments of the end of the duct, and as it was then thought that the duct was formed from the ccelomic epithelium, and as there was no coelom in these segments it was suggested that here it had grown back independently. The present observation renders this improbable.
Fig. 21.^ — Section through the excretory organs in segments twenty-three, twenty-four and twenty-five, twenty-three being to the right, d, segmental duct ; ce, ccelomic epithelium ; nc, nephroccels. The nephrocoels in segments twenty-four and twenty-five are growing towards each other, while the one in twenty-three has met and united with the one in twenty-four. The duct does not show where the two ends of the nephrotomes have united, as in Fig. 16.
Turning now to the anterior end it remains to be shown how the nephroccels become merged with the splanchnocoel. This is brought about simply by the nephroccels in adjoining segments growing together, the process beginning at the anterior end and proceeding posteriorly. Fig. 31 is a sagittal section through the excretory organs in segments twentythree, twenty-four and twenty-five. The nephrocoel in segment twentyfive, the one to the left, has not yet united with the one in segment twenty-four, although the two have approached each other; but the one in segment twenty-four has united with the one in twenty-three. From here forward sections corresponding to the one just given show no signs of nephrocoels, but if the series be followed toward the median line it is found that in the three or four sections before its entire disappearance the coelom presents the appearance of segmentally arranged cavities, showing that the fusion of the nephroccels is not entirely completed. Between segments twenty-three and twenty-four the segmental duct, d, Ig seen to be separated by a narrow space from the ccelomic epithelium.
Geo. C. Price
137
In some of the segments farther forward this is not the case, the two being in contact or actnally fused together. This union is to be looked upon as secondar}'.
Stages A and B previously described follow in natural sequence upon the one we have just been considering, but before proceeding to the gap between B and C, it will be well to pause for a time, and describe a certain phase in the early differentiation of the segmental duct and tubules and also notice some of the mistakes of the earlier paper.
Beginning with an embryo not a great deal older than the last, and corresponding well with the youngest of stage A, it is found that a constriction has occurred in the nephrotome, the most obvious result of which is to divide the nephroeoel into three parts, a dorsal part, which helps to form the lumen of the segmental duct, a ventral part, which later forms
Fig. 22. — Transverse section through the tubule and duct in the forty-fifth segment of an embryo corresponding to stage A of the previous worlj. one, what will later be the cavity of the Malpighian corpuscle ; Id, lumen of the segmental duct ; Itj lumen of the tubule. The line a — & corresponds to the plane of Fig. 23.
Fig. 23. — Oblique longitudinal section of the segmental duct and tubule in the segment from which Fig. 22 was taken, reconstructed on millimeter paper. The plane of the section corresponds to the line a — & in Fig. 22. cmc, what will later form the cavity of the Malpighian corpuiscle ; Id, lumen of the segmental duct ; It, lumen of the tubule.
Fig. 24.- — Section of a tubule in the anterior region where the nephrocoels have disappeared, of the same embryo as the one from which Fig. 22 was taken, t, tubule.
the cavity of the Malpighian corpuscle, and a middle part, which forms the lumen of the tubule proper. This is not apparent in a single transverse section, such as Fig. 22, passing through the forty-fifth segment, but it is brougfit out clearly by the study of a series of sections through a segment, and still better in a longitudinal section such as Fig, 23. This was reconstructed on, millimeter paper, and represents an oblique section, the plane of which corresponds to the line a — & in Fig. 22. The constriction has affected the lower part of the nephrotome, but not to so great an extent as the middle part. A comparison of Fig. 23 with the right hand nephrotome in Fig. 16, from the younger embryo, will
128 Excrotorv Or,uaiis in I'xlcllnstoiiin Stnnti
help to make the matter clear. The jiostorior lialf of the excretory organs in hotli these eniljrvos were reconstructed on millimeter paper. It Avas found that thirtv segments of the older embryo occupied the same space as thirty-one of the younger, so the length of a segment is very nearly the same in the two embryos. It was found further that there was no Inmen in the segmental duct of the younger embryo, but in the older embryo in every segment there was such a lumen, extending in both directions from the tnbule, but more in the posterior than the anterior. The length of each division of the lumen was nearly the same as the length of the nephroccel in the younger embryo, while the width of the tubule was less. It was thus clear that the lumen of the segmental duct had been differentiated from the nephroccel, and had not been formed in the solid rod of cells forming the segmental duct of the younger embryo. This accounts for the fact before noted, that the lumen may extend in both directions from the tubule.
cMc
Fifl. 25. Vicr. 26.
Fig. 25. — Section through a tubule in the region where the nephrocoels have disappeared in an embryo corresponding to stage B of the earlier paper, t, tubule ; sc, splanchnocoel ; Xj part corresponding to the part x of Fig. 26.
Fig. 26. — Section of a tubule which has been cut off from its connection with the splanchnoccel, and from the same embryo as Fig. 2.5. cmc, cavity of the future Malpighian corpuscle ; t, tubule ; sc, splanchnocoel ; x, part that will form the Bowman's capsule of the Malpighian corpuscle.
In an embryo a little older some of the nephrocoels, or better tubules, have lost their connection with the splanchnoccel, by the somatic mesoblast at the point where the splanchnocoel and nephroccel come together, growing down and uniting with the splanchnic mesoblast. In general, the process occurs first in the posterior region, but it does not begin at any one particular segment and from there proceed in regular order, as may be gathered from the fact that on one side in this embtyo the tubules which are closed off are in segments thirty-nine, forty-three, fifty-eight, sixty, sixty-four to sixty-six, and sixty-nine to seventy-one. Beyond this the tubules are degenerate and have almost disappeared. On the opposite side the tubules which are closed off are not quite so numerous, nor do they always occur in the same segments.
In the anterior region where the nephrocoels have disappeared the
Geo. C. Price 129
tubules are J'onneil as evaginations of tlie dorsal walls of the neplirotomes. However, it is not possible to tell where the tuljules thus formed end, and the others begin.. Figs. 22 and 2-i represent transverse sections through tubules of the two regions in a younger eiuljryo and Figs. 25 and 26 represent corresponding tubules in an older eml)ryo. The resemblance in the appearance of the tubules from the two regions is apparent, notwithstanding the fact that there are important difit'erences.
In Fig. 26 the thickening marked x forms ultimately the membrane immediately surrounding the glomerulus; the glomerulus itself appearing in the angle between this and the tubule. In Fig. 25 there is a similar thickening, a% but here it later entirely disappears, the tulnile retains the characteristics of a pronephric tubule throughout life, and no glomerulus is ever formed. The attention was first called to the similarity of the two kinds of tubules in the above particular while searching for indications of the formation of glomeruli in the anterior part of the excretory organs. It is here given for what it is worth, although it might be interpreted as suggesting that formerly the anterior tubules as well as the posterior were provided with glomeruli.
By the disappearance of the nephroccels in the anterior part of the body, and by their 2>ersistence and subsequent separation from the splanchnocoel in the posterior part, the excretory system becomes quite early divided into two regions; but for a long time it is impossible to determine the exact lioundary between the two, owing to the fact that there is an intermediate region of a few segments, in wliieli the nephroccels have neither merged with the splanchnocoel nor have they Ijeen cut off from it, and there is nothing to indicate which their ultimate fate will be. Moreover, in front of this the nephrocot'ls do not end abiiiptly but become gradually shallower and shallower. Later the boundary becomes definite, Init it is not constant for different individuals, nor is it always constant for the two sides in the same individual. The l)est that can be said is that it is in the neighborhood of the thirtieth segment.
Corresponding to the above described regions there are two Idnds of excretory tubules, those in the anterior region retaining the characteristics of pronephric tubules throughout life, while those in the posterior region assume the characteristics of mesonephric tubules. These terms would be employed in speaking of them if it were not that it would lead later to the contradictory expression, "" the mesonephric tubules of the pronephros." For this reason the first will be spoken of vsimply as the open tubules, and the second as the closed tubules.
Of the closed tubules those in about the last eighteen or twenty segments degenerate (the number not being constant), wdiile the remainder
130 Excretory Organs in Bdellostnina Stouti
persist, and all except a small nnniber at the anterior end become mesonephric tubules of the adult.
Both of these points were noted in the previous paper, but it was there stated that in the oldest embryo of stage B the tubules had disappeared in the last nineteen segments. A subsequent very careful examination proved this to be a mistake. They have disappeared in the last eleven segments, but in the next eight they are still present in a rudimentary condition. Their entire disappearance does not occur in this region until quite a little later.
In the earlier paper the statement was made that the series was sufficiently complete to enable one to say that the mesonephric tubules of the adult were derived from tubules which in the embryo arose as pronephric tubules. The opinion has been expressed by some authors that the evidence given was not sufficient to justify the assertion, and it is not to be denied that, on account of the wide gap between stages B and C, the objection may have been reasonable. But an examination of specimens both older and younger than those before studied, as well as of quite a complete series between B and C, has proved the truth of the statement. In no case in the region of the mesonephros of the adult is there the slightest indication of the disappearance of one set of tubules and the appearance of another, but on the contrary the first tubules to appear may be traced into what can be none other than the mesonephric tubules of the adult.
Wheeler ^ objected further on the ground that in a young specimen of Myxine Mass found mesonephric tubules forming in the posterior part of the body independently of the duct. As a matter of fact Mass " describes and figures two well developed Malpighian corpuscles, one with and the other without a tubule, neither of which is in connection with the duct. He does not state, however, whether these occur in segments in which later mesonephric tubules are invariably present, and until this is known it seems at least possible that the structures in question may be degenerating instead of developing tubules. However it may be in Myxine in Bdellostoma in a few cases very small, degenerating tubules have been found far back in the body, independent of the duct. But liere a comparison with other tubules in the same embryo, as well as with embryos both older and younger, shows that these have been
^Wheeler, W. M.: The Development of the Urinogenital Organs of the Lamprey. Zool. Jahr., Vol. 13, Anat., 1899.
■•Mass, Otto: Ueber Entwicklungsstadien der Vorniere und Urniere bei Myxine. Zool. Jahr., Vol. 10, 1897.
Goo. C. Price 131
pinched oil: from ilie (hiel nnd would soon entirely disiippear. As a rule the degeneratiiii;- tubules do not beeome thus separated from the duct.
In the earlier paper the -statement was made that the excretory system developed from behind forward. This was based on two facts; first, in passino; from the anterior end backward through a number ol' segments in both stages A and B, both the duct and tubules became gradually better and better dilTerentiated ; and second, in the older embryo the system extended a little farther forward than iu 11 le younger. From the last it was assumed that if the younger embryo had developed the system would have extended as far forward as in the older, but this does not follow, as is proved by the examination of a larger number of embryos. The above ojnnion was further strengthened by the observation that the first tubules to be cut off from the connection with the splanchnocoel were at the posterior end. From the material at hand it cannot be determined which are the first neplirotomes to appear although it would seem that those at the posterior end are the last. The formation of the excretory system proper seems to begin in a good many segments at about the same time, but the d(>velo]iinent lags heliind at the anterior end, and this gives lise to the appearance in certain stages of this being the youngest part.
The mistake of looking upon the anterior end as the youngest part led to the more serious error of supposing the nephrotomes were pockets formed from the unsegmented mesoblast; for at the anterior end where the tubules were apparently just appearing there were no indications of nephrotomes. the tubules being connected with the unsegmented bodycavity. Then in passing back, as the tubules became better and better developed they were connected at first with very shallow pockets and then with deeper and deeper ones. We now know that this appearance is due not to the formation of segmentally arranged pockets, but to the disappearance of nephrococls. In a review Felix' pointed out the probability of this error.
Til what was supposed to be the youngest part of the system the segmental duct was found to be in connection with the coelomic epithelium. This union is seeoiulary, but it was then thought to be primary, and it was supposed that the duct in all parts arose as thickening of the ccelomic epithelium. The theory was strengthened by finding the duct in connection with the coelomic epithelium in one individual in some of the
° Felix, W. : Die Price'sche Arbeit "Development of the excretory organs of a Myxinoid (Bdellostoma stouti Lockington)" und ihre Bedeutuiig fiir die Lehre von der Entwickelung des Harnsystems. Anat. Aw/.., Vol. 13, Nos. 21 and 22, 1897.
132 ]v\cretory Organs in Brlellnstoma Stouti
posterior segments. But in younger embryos the dnct has since been found in sections wliere the splanchnocoel had not yet been formed.
In the anterior region the duct is occasionally either partially or entirely absent between two tubules. Tliis is to be looked upon as due either to degeneration or to the failure of the duct to develop. In an extreme case, in an embryo of stage B, tliere was a Ijreak on one side between tubules one and two, five and six, seven and eight, eight and nine, and fourteen and fifteen, and on the otlier between one and two, five and six, and nine and ten.
We now come to the differentiation of the pronephros of the adult, the most important steps of which occur in the stages between B and 0, and were therefore not seen at all in the previous work.
In the oldest embryo of stage B the anterior end of the body was injured, so that the position of the anterior end of the excretory organs could not be accurately determined, but it was estimated that the system had disappeared in about nine segments. It is true that some of the anterior tubules may degenerate, but in no case in the material in hand, where the point could be accurately determined, can it be said that so many as nine have disappeared, so that the above estimate must be considered erroneous. What was said regarding the pronephros in embryo C was of rather a tentative nature, the preservation not being of the best, and it being impossible to work out the structure satisfactorily.
In the youngest embryo before studied the gill-slits were found Avell forward in the head region, while in the oldest they were well back in the body region, occupying the same position as in the adult. On entirely insufficient evidence it was assumed that the change had been brought about by slits degenerating at the anterior end and new ones being added at the posterior end, and that, in the course of development a good many more slits appeared than were present in the adult. Dean ^ has shown that this is wrong, the first slits formed being permanent, but shifting their position from the head region to the body region. This change in the position of the gill-slits seems to be the cause of an important change in the excretory system. At all events, as the gills become shifted farther and farther backward the anterior tubules become crowded closer and closer together, until finally they form a small, compact body, the pronephros of the adult, in the region a little posterior to the thirtieth segment. The crowding affects all of the open tubules,
"Dean, Bashford: On the Development of the California Hagfish, Bdellostoma Stouti, Lockington. (Preliminary Note) Quart. Journ. Micr. Sci,. No. 158. Vol. 40, 1897.
Geo. C. Price 133
and a small though varialtle luimlier of the closed tubules as well. At all times the anterior end of the excretory 'systeui is a little back of the posterior end of the branchial system. For quite a long period tlie history of the differentiation of the pronephros of the adult is simply a history of the crowding together of the tubules, as will appear from the following account of the organ in a series of embryos of different ages. Before beginning, it may be stated that in all cases every section of the parts described was drawn, different colors being used for the different tubules. This was highly advantageous in all cases, and was absolutely necessary in the older and more complicated specimens. The arrangement is not usually exactly the same on the two sides, but unless there is some really important difference only one side will be described.
The first embryo of the series is a little older than the oldest of stage A, and the process of crowding together of the tubules has just fairly begun. The first tubule is in the sixteenth segment and is not conr.ected with the rest of the svstem. In segments sixteen to twenty-four,
Fig. 27. Sagittal section ttirougli tlie auterioi- end of the excretory organs in au
embryo in which the tubules are beginning to be crowded together, formed by the combination of two adjoining sections. There are here five tubules in the space of three segments. (J, segmental duct ; t, tubules.
that is in nine segments, there are twelve tubules. Back of this the position of the tubules has not been affected. If all were arranged segmentally the first tubule would be in the thirteenth segment. The first three or four tubules are not so well developed, as the following, and look as if they might be in the process of atrophy, although this is not at all certain. Fig. 27 is a combination drawing made from two sections, showing five tubules in the three segments, twenty to twenty-two. There is quite a little space as yet between the tubules. The segmental duct is almost without a lumen, but a little further back the lumen begins, and continues witli only a few interruptions to the posterior end of the duct. However, the duct does not open to the exterior.
In the next embryo the first tubule is in the twenty-secoiid segment, and in the six segments, twenty-two to twenty-seven, there are fifteen tubules. Thev are not evenly distributed, being more crowded in the anterior part than in the posterior. But in no case are two tubules in actual contact with each other. One or two at the anterior end are quite rudimentary, and there was some doubt as to whether they actually
13-i Excretory Oi'g.ins in Bdellostonia Stouti
representeJ tubules. All arc connected with the segmental duct. If they were arranged segmentally the first would be in the thirteenth segment. This embryo was sectioned transversely, and it could be determined accurately that the tubules in the thirtieth segment were the first to be closed off. However, those in the twenty-ninth segment looked as if they might be closed off later.
The first tubnlc in the next embryo is in the twenty-fourth segment. It is not connected with the rest of the system and is separated by quite a wide space from the second, which is in the twenty-fifth segment. In segments twent5'^-five to thirty there are sixteen tubules, and of these the first ten, which are in the space of three segments, are so closely crowded as to be almost if not quite in contact with one another. If all were arranged segmentally the first tubule would here be in the fourteenth segment.
In the next embryo there are seventeen tubules in the four segments twenty-seven to thirty. Of these, the first thirteen are in so short a space that there is not room for them to stand in a row one behind the other, and some are beginning to be crowded to one side — a process which is carried much farther in older enibryos. A comparison of Fig. 28, taken from this embryo, with Fig. 27, shows how much closer together the tubules are here than in the younger embryos. The coelomic opening of most of the tubules shown in Fig. 28 are found in other sections. The segmental duct is no longer straight, and so does not show in the full length of the figure.
The next embryo is particularly interesting, because here the crowding process has affected not only all of the open tubules, but the three anterior closed tubules as well. The posterior limit of what will be the pronephros of the adult may be placed, with some degree of probability, between the third and fourth closed tubules, for at this place the segmental duct shows some slight indications of degeneration. Owing to an injury in the anterior region of the body, it is not possible to determine the exact position of the pronephros, but it occupies the space of a little less than two segments. There are in all twenty-one tubules_, eighteen open and three closed. The first and second tubules are connected with each other, but not with the rest of the system. The three closed tubules have the same structure as those farther back, and are in direct line with them, but they occupy the space of only three-fifths ol fi segment, and the third slightly overlaps the second. Just at the point where the anterior closed tubule joins the duct, the latter bends downward, backward and slightly outward, and then turns and runs again forward, thus forming a sort of s-shaped bend. In this way some of the
Goo. C. Price
i;35
oiHMi iul)u!(\'^ coiiu' to lie v(Mitral to the closed tubules, and also slightly more lateral, and a transverse section may show parts of one or even of two closed tubides, and at the same time parts of several open tubules. Fig. 29 represents such a section. 'J'he pronephros now forms a prominent body projecting into the crelom. The segmental duct is cut through its posterior bend, and four open tubules are seen to be in connection with it. By running along the series the lumen of these may all be traced to a eoniuM'liou widi the duct on the one hand and with the coelom on the ofhei'. Above, one of the closed tubules is cut through its full length, but tlic lumen appears only at the point where it joins the duct. Farther on in the series it niav be ti-aeed to a connection with the
M.G
Fig. us.
Fig. 29.
Fig. 28. — Sagittal section showing parts of seven tubules, and illustrating the way in which they become crowded together. In studying the series all the tubules are found to open to the cujlom. cm, coelom ; hv, blood-vessels ; d, segmental duct ; t, tubules.
Fig. 29.- — Section of a pronephros showing the two kinds of tubules, four open tubules below and a closed tubule above, cnic, cavity of the Malplghian corpuscle ; d, segmental duct, here shown in two places ; yl, glomerulus of the closed tiihule ; t, tubule.
cavity of the jMalpighian corpuscle. There are places in tlie pronephros where the segmental duct has no lumen. This is the first embryo in which the segmental duct was observed to open to the exterior at its posterior end.
In an embryo slightly older than the last, the pronephros was not thoroughly studied, but it was observed to be more sharply set off from the mesonephros than in the last, although the segmental duct was still continuous between them. It occupied parts of the thirty- third and thirty-fourth segments. The number of closed tubules was not determined, but two glomeruli were seen to be in very close contact with each other.
The next embryo is somewhat younger than embryo C of the previous
130
l']x('rot()r\- Orii'iins in Bdellostoina Stoiiti
paper. Tlio ])r()iu'|)liros on the ri^lit side is in segments thiitv-two and thirty-three. There are in all twenty-one tuhnles, and of these the first three have no connection with the segmental dnct, while the last three can be traced to a connection with Malpighian corpuscles, and must therefore represent closed tubules. On the left side the pronephros is in segments thirty-three and thirty-four, and there are here nineteen lubules instead of twenty-one. The first two are not connected with the duct, and two instead of three reisresent closed tubules. If the tubules were arranged segmentally, the first would be in segment thirteen on the right side and sixteen on the left, while the anterior closed tubule would be in segment thirty-one on the right and thirty-three on the left. On both sides the pronephros is connected with the mesonephros by the segmental duct, and in neither case does it occupy the full width of two seo-ments.
Wb.v
Fig. 31.
Fig. 30. — Sagittal section through the pronephn.s showing several open tubules, all but two of which are cut in longitudinal section. In this embryo the limits of the pronephros are definitely established. hCj blood corpuscles ; d, segmental duct ; *, tubules.
Fig. 31. — Transverse section through the pronephros of the oldest embryo studied, showing one of the open tubules, t, in the process of branching, bv, blood-vessels; f/l, glomerulus.
Fig. 30 represents a sagittal section through the left pronephros. Several tubules lie in about the same plane and are cut longitudinally. Their connection with the segmental duct is shown. Two are cut transversely. Farther on in the series these also join the duct. The section is not near enough the median line to show an)' of the glomeruli.
In the last embr3'o to be considered, which is some little older than the embryo C, the exact position of the pronephros could not be determined, owing to an injury farther forward, but it is located in the
Geo. C. Price 137
pericardial cavity, in a position corresponding to that of the adult. There are on the left side twenty tubules, two of which can be traced to a glomerulus and must therefore represent closed tubules. Some three or four of the open tubules have begun to branch, as is shown in the one in Fig. 31. This is the beginning of a process which results in the formation of the scores of pronephric funnels found in the adult. The two closed tubules are small and insignificant, but the glomerulus to which they go is large and well defined, and has something the appearance of having been formed by the fusion of two glomeruli. At one point, shown in Fig. 31, the cavity at the side of the glomerulus, the cavity of the Malpighian corpuscle, is almost in communication with the coelom. This is interesting as suggesting that in some cases the communication might actually occur, in which case the glomerulus would be virtually in the body-cavity. However, this is to be regarded as only a passing remark, and not as suggesting a homology between this glomerulus and the glomus of the pronephros in other forms. ISTothing of the kind occurs on the other side, nor has it been observed in any other embryo. There is a complete break in the segmental duct between the pronephros and mesonephros. In the pronephros itself the duct is distinct and the lumen well defined through about half its course on one side and two-thirds on the other. In the rest it is solid, and in places quite small. It may be remarked that no case has yet been observed where the lumen of the duct is continuous throughout tlie entire pronephros.
A point that has not been worked out is the manner in which tlie segmental duct becomes shortened as the tubules are crowded together. The bending of tlie duct previously described accounts for part of it though hardly for all.
The account of the pronephros just given does hot fit in well with Mass' ' description of this organ in a 3'oung specimen of IVIyxine. wliei'o there is no segmental duct; but the difference is hardly to be accounted for on the supposition of errors of observation in either the one case or the other, nor is it likely that later the pronephros of Bdellostoma would come to be more like that of the young Myxine. An examination of the pronephros of the adult Bdellostoma reveals the presence of a true segmental duct, although it may not be continuous through the entire organ, while, judging from the published accounts of the pronephros of Myxine, the presence of a true segmental duct here would seem to be very doubtful. In the light of iJiis the above discrepancy is not surprising.
'Mass, Otto: 1. c.
138 Excretory Organs in Bdellostoma Stouti
The presence of the excretory organs in segments where later the gill slits were found, was formerly thought to constitute a resemblance between the excretory system of Bdellostoma and that of An^phioxus, in which the position of the excretory system and branchial system coincide, but this opinion is no longer held.
WILHELM HIS. His Relation to Institutions of Learning.
BY
FRANKLIN P. MALL. Professor of Anatomy, Johns Hopkins University.
The ancient science of anatomy has been perpetuated and extended during the many centuries of its existence by great men who have dedicated their lives to it. The list is a long one for the development of the science has been slow and progressive from the earliest ages to the present time; we find in it on the one hand, some of the names of the greatest who have ever lived — Aristotle, Vesalius — on the other, the names of those who rank as leaders of a generation, Bichat, His.
Undoubtedly the reason for the continuous progress of anatomy through so many centuries is that man has always shown an interest in a knowledge of his own structure and, in turn, that this knowledge has been of great service in battling for rationalism against mysticism in many directions. But in order that a science may progress, it must be in the hands of able men with the highest ideals and with inexhaustible zeal. The full benefits of a science cannot be obtained from its literature alone; it is well known that countries without leaders in a science live almost in ignorance of it. No science will develop to its fullness unless it is represented by men who are great enough to grasp the science as a whole and broad enough to understand its relation to cognate sciences as well as to the needs of a civilized community.
A man of this caliber was Wilhelm His. He was born of a distinguished family which felt that it owed much to the community and therefore educated its children for a strenuous life to be dedicated to the community. He was in no sense a self-made man though he had in him the qualities to make one; his powers were fortunately developed under the best possible conditions. His father taught him, by example, simplicity in living, clearness of thought and seriousness of life. His mother, who died while he was still a youth, guided his education Avith the greatest care, laying much stress upon a good command of German. In a pri American Journal op Anatomy. — Vol. IV. 10
MO Williclm II is
vate sc'lmol in a t'ountrv town, he received a ii-aiiiing so rigorous that it makes one sluulder to tliiiilv of it. At the age oi' tiiirteeii, he returned to his home in Basel and entered tiic (i3'nmasiuni from wliieh he graduated five years later, in 1849/ During his years in the Gymnasium, His rated only as an average pupil, for his bent toward physics and natural history was great, and what spare time he had was devoted to these subjects. He also photographed a great deal, the art then being still in its infancy; he constructed his own camera and made his own plates. Tn those days the professors of the University taught also in the higher classes of the Gymnasium (the Pedagogium, as it was called), and it was from them that he received his greatest inspiration. Especially grateful was he to the Professor of German for a thorough training in the use of the German language in which he had received such a good start in his father's house.
Throughout life the good command of language he had gained and the marked technical ability he had ac(iuirod were of the greatest use to him in furthering the cause of anatomy; it is interesting to note that these powers were developed long before he entered the University. It was fortunate for him and for anatomy that he came under the influence of able men early in liis career.
]\rost of his student friends had decided to study law and naturally His thought that he must accompany them. JTis inward feeling was drawing him towards natural history, but he felt that one's inclination is to be viewed as a forbidden fruit and therefore he had nearly decided to go with the stream of his fellows. Before taking the final step, however, lie consulted his superiors, one of whom was Winscheid, later one of the foremost jurists of Germany. Winscheid advised him to follow his own bent and tins carried him into medicine.
As soon as he became a student of medicine in the university, he found' himself free to follow his own inclinations. For the first few years he devoted most of his time to the sciences. Anatomy, physiology, natural history, psychology, chemistry and geology were studied at Basel and Bern under a variety of men. He soon learned that for the student, the quality of the teacher is more important than the sul)ject taught; in order to have a great teacher and tlic important subject together, he decided to study anatomy with Johannes ]\riiller, in Berlin.
The lectures of Miiller were a revelation to him and ho felt for the first time the inspiration of a strong personality. His learned from Miiller and later from Peniak, how great an inll nonce a teaelier can have upon a pupil, when, as an authority, he presents his own line of work. Then the teacher and pupil stand upon the common field of nature. The
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power of the successt'ul explorer is most stimulating, it eneourages the pupil to attaek open problems, and, if he can, he formulates questions and takes his position towards them. Thus j\Iiiller's presence worked upon His and unconsciously the latter soon found himself in the library studying ]\Iiiller's monographs.
His also pursued a course in embryology M'ith Remak in Berlin. The subject was then a new one, but it made a profound and lasting impression upon the young student for it showed the relation between histology, embryology and comparative anatomy. To Eemak, His owed more than to Miiller, for Eemak's teaching helped him to formulate problems which occupied him during the following half century; his efforts to solve them, have, in many respects, changed the aspects of anatomy.
How different is the study of medicine in Europe from that in America! There freedom reigns and students wander from place to place being controlled only by a fairly rational system of examinations in case they wish to graduate. Weak students fall out, for there is no cram system to drive them onward ; able students select great men as teachers and thereby develop themselves and become stronger. So His, soon tiring of the sterile lectures in practical medicine, turned his eye towards a new star which w^as beginning to illuminate the medical w'orld and wended his way to Wiirzburg to study wath Virchow. During one of Reinhardt's lectures. His had happened to see Virchow's great paper upon connective tissue which had just appeared and it made so great an impression upon him, that he at once decided to go to Virchow\ He was then far from prescient of the fact that in a few years he was to take an important part in the great discussion which Virchow had opened."
In the early fifties, the University of Wiirzburg was at the beginning of that rapid rise coincident with the appearance there of a brilliant band of young professors. The change was brought about largely by a reformer. Professor Reinecker, through whose personal efforts Virchow and Kolliker w^ere secured. It was the good fortune of His to enter this atmosphere; a select faculty was chosen by a talented student. He entered Wiirzburg at the beginning of his fourth year of medical study and began to work in the clinics. He soon found that the laboratories attracted him more than the clinics and during three semesters much time was devoted to practical chemistry; the weekly meetings of the Scientific Society always found him present to hear of the new medicine from Virchow and Kolliker.
For a time he attended regularly a kind of journal-meeting at Kolliker's house wdiere a variety of scientific subjects were discussed. There
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he became acquainted with Ludwig's physiology which was then heterodox and called forth severe criticism. Ludwig, very critical towards others with pupils who were more so, kept the camp stirred up pretty well; this had the right eifect upon his critics (His included) for they studied the new physiology. Converts were made at a rapid rate and before His had reached middle age, he found that both Virchow and Ludwig were very orthodox; the scientific world had come to them.
In Wiirzburg, a great opportunity came to His — Virchow at once set him at work in a good field to answer fundamental questions. Probably the most important step in the life of a scientist is to be started aright in research after a good preliminary training. The earlier this is done the better. His was twenty-one years old, mature for his years and he was given every opportunity to use all of his ingenuity and strength in
answering important questions. Plenle and Virchow had crossed swords, 'but this did not make the great pathologist try to enslave the mind of His in order to win a victory, but now as so frequently afterward, a desire to know and to understand were Virchow's only considerations in directing a pupil in his work. The results of His were not what Virchow had anticipated for they showed that Bowman's corneal tubes and Coccius' serous spaces were artifacts and had nothing whatever to do with the system of connective-tissue spaces described by Virchow. But His was encouraged to continue and the monograph upon the cornea which he published a number of years later has proven to be a standard until the present day. His had been in the arena and had shown his prowess ; he had originality and strength as well as training from a great master and henceforth during all his life he was to win victory after ^victory for science.
It was still necessary for His to take his medical degree and as was customary with many at that time, he proceeded to Prague and A^ienna to study with the great clinicians there. At the end of a year he returned to Basel and passed his examination with the highest mark.
The young student had received the best from his home, the school, the gymnasium and the university of his native city, had wandered for four years studying at famous foreign universities receiving information and inspiration from the greatest masters — ^Miiller, Virchow, Kolliker and many others — and had now returned to Basel to receive his degree. How much longer must we wait for similar privileges in -America ?
The following three years of leisure and lack of responsibility, those in which the real stuff in a scholar is tested, were devoted to a continuance of the work already so well begun.' Part of the time was passed in his private laboratory, one of the years being broken by a journey to
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Paris, another by a visit to Berlin. Throughout this period he associated only with the best, for there was a never-wavering desire in him to devote his life to science. During this time he became a Privat decent in the University of Basel and gave regular lectures there on histology.'
In most of the continental universities any person approved by the faculty may teach and thus new blood is constantly being infused long before a fogy or a dog in the manger has been removed by a beneficent Providence. There is thus maintained a constant competition for better teaching within the walls of the' university, and strong young men are brought to the front. If under tliese conditions a young scientist takes deep root without being spoon-fed or coerced, and commands a broad field, adding to its borders, the greatest assurance has been given that he will remain active and productive until he is three score and ten. In America, we frequently find recent graduates who tell us that they would follow an academic career if their future were assured as far as salary is concerned. Little do they realize that this attitude of mind alone should exclude them absolutely from such a career. Unfortunately, we seem to have some university presidents who are as easily deceived by such " scientists " as the public is by a Mesmer. Within a year, I have known of a president Avho, when seeking a great anatomist for a rich university, selected a man who had done no scientific work whatever and had never been tested, simply on his own assurance that he would " try to do something."
In 1857 the chair of anatomy at Basel became vacant, and, as is customary, the faculty sought the best available man. They found in His an able earnest young scientist of the best training, tested through freedom and research, whose work had been continued with increasing successful results through the three years of leisure following his advancement to the doctorate. A man who had studied a subject' for its own sake ° and had contributed to it, was more likely to represent it well than one who had studied it for other rewards. Only too often do we see scholars whose work is good and imitative, but net profound, shift from one thing to another in order to keep before the public in an upward career; they find themselves sterile at forty and have to be shelved in some good berth as an active " pensioner," at fifty. To avoid this danger, great productive men must sit in faculties, for they alone are able to recognize genius' in a young man.
When the Chancellor of the University informed His of his appointment as professor of anatomy and physiology, he said : " We have thrown you into the water, learn to swim;" and the remark was appropriate, for the new profes?or had never served an apprenticeship in the teach
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iiig of either aiialoiny or physiology. Oiteii did he seem to sink but he always came to the surface again, for he had overcome great difficulties before — he was independent. After all, research i.s to the proljloni of teaching as manoeuvres are to a battle.
The power in His now blossomed and bore fruit. AVith his great background he was able to construct strong courses, marked by his individuality, and soon he was to influence the leaching of anatomy the world over. The attitude of the comparative anatomist he had learned from Johannes Miiller, that of the Jiistologist from Yirchow and Ivolliker, but that which made the greatest and most lasting impression upon him was the attitude of the embryologist which he learned from Eemak. The histological work begun M'ith Yirchow was continued and soon extended to include the lymphatic system. In 1862 he published a paper on h'mph radicles, advocating a closed lymphatic system, by all odds the best paper on that side of the question which has ever been published.
During this time, his embryological studies were also actively prosecuted for he had learned of their great value in histology from Eemak. The classic object, the chick, as well as the structure of the ovary was studied again. That a plan underlay his work was very apparent, but no one dreamed of its magnitude until the publication of his academic program in 1865,' entitled "Die Haute und Hohlen des Korpers." In this paper he gives the key by which the genetic relation of tissues can be ascertained and following it faithfully, he made one discovery after another. The " Program " is now incorporated with our science ; it proved to be really a program for anatomy, and it was fitting that it should have been reprinted as the last paper during His's editorship of the Archiv fiir Anatomic, nearly forty years after its first publication. It certainly must be gratifying to a scientist to see his early dreams so well realized before his work is over. As His said of Bichat, " It is a mark of genius to see great truths in a relatively small number of observations."
The great contribution to anatomy during the eighteenth century was the discovery of the tissues, the conception of which received its full development in the general anatomy of Bichat, published in 1801. Cellular tissue had been gradually making its way during that century and among others, Haller was trying to see in it some imit of organization, but the cell of Haller proved to be only a connective-tissue space and the all-important fiber was viewed by most anatomists as an artificial production. But the doctrine of cellular tissue was the foundation of general anatomy and this in turn that of histology which, through embryology, has given us modern anatomy.
During the nineteenth century Ave see three great steps in anatomy.
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general anatomy, associated with the name of Bichat, the cell doctrine with that of Schwann, and histogenesis with that of His. Compare the great text-books of anatomy of 1790 with those of ISIO, those of 1830 with those of 1850 and those of 1880 with those of 1900 and the reasons for this statement will be apparent.
At the time His began his embryological studies the plan of the development of the vertebrate bod}', as enunciated by Von Baer with Eemak's classification of tissues, had been accepted generally. But the work of Eemak was incomplete and in some respects unsatisfactory as, for instance, his conclusion regarding the development of the nervous system, the central portion of which he believed arose from the ectoderm and the peripheral portion from the mesoderm. This and other defects were corrected by His who made a new classification of tissues and germ la3'ers which differs more from Eemak's classification than this in turn did from. Yon Baer's.
In the " Program " His also showed that there is an embryological foundation for Bichat's classification of membranes since they are related directly to the germ layers. Further, he extended the conception of the serous spaces to include the vascular system. All of the serous spaces arise in the mesoderm, and His showed that they are lined with a special kind of cell, designated from the time of his paper on, as endothelial.
After this, his greatest work was histogenetic — witness for instance his studies upon the nervous system and upon the development of the bloodvessels. Contribution after contribution was published upon histogenesis. During the last years of his life he often complained to me that his time was short and that it was necessary for him to make haste in order to round up his work.
Thus His continued to l)e active until he was over seventy years old; his final papers, " although fragmentary," are of the highest quality. In his great paper upon the angioblast he gave his latest classification of tissues from an embryological standpoint^ and stated in conclusion that the riddle which had interested him so much still remained unsolved. Similarly, in his last monograph upon the nervous system, he wrote: " The notes are not to be considered as a report of a finished research, but thev only indicate the line of work which must be followed by united effort* in order that a better understanding of the structure of the brain may be gained." He saw more and more clearly that many hands are required to survey these great fields and during the last twenty years of his life, thought much about the organization of research. He lived to see his efforts in this direction crowned by the establishment of a com
146 Wilhelm His
mittee for the study of the brain by the International Association of Academies, of which more presently.
In 1872^ the chair of anatomy at Leipsic became vacant and through the efforts of Ludwig, His was secured. Professor Ludwig told me that it was by no means the unanimous will of the faculty to call His, for in general he was not well known, nor was he considered a good teacher. But Ludwig knew his man for he had found in His the strongest opponent of his notions regarding lymph radicles ; furthermore, he was fully able to appreciate the author of the great academic program on " Haute und Hohlen.-'^ ' For over thirty years Ludwig and His were colleagues, consulting each other almost daily, an ideal relation for great scientists.
The work of His had branched in many directions at Basel, but it grew with increased vigor at Leipsic, for here he had all the material aid he could desire. Photographer, modeller, mechanic, technician, artist and others were at his command. A new laboratory, which proved to be a model, was built according to his ideas. Each of these factors was to play a part in the campaign he was conducting and it was soon "seen how his hands were thus extended.
Through the better technical assistance. His increased his productivity, for his plan was broad enough to use it to the greatest advantage. The members of his staff, however, were never subject to his orders in their scientific investigations, nor did he ever use " research assistants " for his ethical standard would not permit such employment of scientists. That a great man can increase his productivity enormously without the questionable use of young colleagues is shown by example in the life of His. Furthermore, his plan of organizing research is one of the best from both the ethical and the scientific standpoint.
The microtome which His had invented in Basel was now perfected and better serial sections were made of embryos of different classes of vertebrates than ever before. The great monograph upon the chick had just been published and smaller but equally important papers appeared upon fishes; these were soon to be followed in 1880 by the first part of the monumental work upon human embryology.
Throughout his embryological work His was constantly interested in the broader problems and he was among the first to view development from a mechanical standpoint. His views and general plans were brought together in 1874 in the classic, " TJnsere Korperform " dedicated to his new colleague, Ludwig, appropriately for in it the subject of development is presented from a physiological standpoint. These views were immediately antagonized to the utmost; when arguments failed, his opponents resorted to ridicule, but, in general, His held his
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own and continued a forward course. He now became the leading advocate of the theory of mechanics in development and it subsequently tinctured all of his papers. Although he made no experiments upon the growth of animals, he must be viewed as one of the pioneers of the new, science of experimental morphology.
Throughout His's embryological papers we see that he believed that the form of the animal body, as well as of its organs and tissues, is due to mechanical influences of the structures upon one another. This conception was often erroneously construed as meaning that there is a mechanical cause for growth, but His repeatedly denied this. " The stimulant which causes cells to multiply cannot be traced to mechanical influences." His mechanical conceptions of development are comparable with the study of the mechanics of the circulation rather than with that of the evolution of the heart. When analyzed, it appears to me that his mechanical conceptions are related principally to the wandering of tissues and organs in development. One of the best examples of His's ideas is his conception of the growth of nerve fiber from the central cell to the periphery, where, through secondary connections, it makes itself fast to its end organ. With this conception, we can understand and picture to ourselves the formation and the infinite number of variations of the peripheral nervous system. Other examples may be found in the wandering of the diaphragm and in the metamorphosis of the branchial arches. Mechanical influences must guide these structures to their fate. And finally, great masses of tissue wander in the embryo long before we can see what is to become of them. The best example of this kind is to be found in the early development of fishes formulated in His's brilliant theory of concrescence. According to His, the word "mechanical" is to be applied to the movements of these avalanches of tissues and their influence upon one another in gaining their final position and not to the cause of growth.
One of the characteristics of His's embryological work is that he viewed the embryo as a whole ; he always approved of embryological papers which carried a subject to its logical conclusion.'" As he improved the microtome more and more, so that he could cut serial sections fifty microns thick, he constantly kept in mind the relation of the individual section to the embryo as a whole; this led to his well-known method of graphic reconstruction in 1868. At that time haphazard sections of an embryo were often compared with chance sections of older embryos which led to all kinds of erroneous conclusions. In the course of time, he perfected his method by drawing an enlarged picture of the embryo upon ruled paper into which he projected in their proper positions the sections
148 Williolm TT
enlarged to the same scale. Photogra])hy, as well as a new instrument which he invented, the embryograph, aided him in his work. In order to be better able to compare stage with stage, the reconstructions were converted into models which were duplicated by Ziegler; these models now form the most valual)le asset of many of the embryological museums the world over. More accurate models can be made by drawing the sections upon wax plates which when placed upon one another reproduce the embryo ; this method, invented by Born, was used to a very great extent by His in his later years.
Until this time the embryological campaig-n had been conducted by His from all sides, but one great fortress, the human embryo, still stood before him. Human embryos were very difficult to obtain and the literature npon the subject was meagre and poor, but His -was soon able to select a few important stages from a mass of poor material, normal and pathological. These he studied with such care that the knowledge of the anatomy of the human embryo now exceeds that of any other animal. To be sure the earliest stages were missing, but this mattered but little, for being master of the whole field of anatom}^, he was able to produce a model work. Each chapter in his monograph is great and original, giving a mass of information; the work reaches its climax of interest and value in the part on the nervous system.
During the last dozen, years of his life, His's attention was taken away from the study of the nervous system by a variety of subjects; thus, for example, he was interested constantly, as his letters show, in the embryology of fishes." The work on this latter snbject he was able to round out, but it seemed as if his promised work upon the brain would never appear. When I visited him the summer before his death, I found a broken man, working away at a large manuscript which by no means satisfied him. What could be arranged, was published in a monograph upon the brain, which will serve as a foundation for investigation for many years to come. He had hoped to write another volume, but his illness rapidly grew worse, and, unal)le to work longer, a week before his death, he wrote that his remaining wish was that the end might come soon.
The technical ability of His which had been pretty well trained in the gymnasium, gradually developed farther and proved to be of great value to him as a teacher. Optical instruments of all kinds, magic lanterns and microphotographic apparatus were much used by him ; demonstrations with the microscope after each lecture aided in illustration. The pictures wdiich he drew npon the board vrhile lecturing were models of their kind and he developed them before the students in such a manner
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that they could be copied gradually while being evolved. The subject matter of his lectures was chosen in a very conservative way, the substance being always sound and free from all kinds of wild theory and speculation.
Early in his career, h.e had inach^ crude models of the mesentery and the like, for these were subjects the forms of whicli Avere dilTicnlt to understand. Toward the end of the seventies, modelling was prosecuted on an extensive scale with the aid of the modeller. Steger, resulting in a series of papers on the form and ])osition of the organs A\hich are now standard. His many models have been duplicated and fill an important corner in all anatomical museums; they have made His the founder of a new school of topographical anatomy. The method which His had introduced in embryology were thus also applied to gross anatomy, for he was never satisfied until he could see adult forms in the embryo and the outlines of the embryo in the adult.
In His the power of visualizing forms — the power which enaliled him to do his work of reconstruction, to make those wonderful blackboard drawings during his lectures — was developed to an extreme degree. This power was one of his principal gifts, and one of the chief foundations of his achievements in science. As he grew older there was not only an increase in the depth of insight into problems, which is natural in so able a man, but also what is rarer, a very great improvement in the power of expounding his results. His last papers are models, characterized by conciseness of style, great clearness of description and a suppression of all superfluous details.
While His Avas teaching and investigating, the question of nomenclature came up. Each century, each country, each school, each specialty and each teacher seemed to have a particular group of terms based upon an imaginary normal ; the result was that there Avere so many normals that it Avas extremely difficult to construct a table of synonyms.
AVhen His and a few others founded the Anatomische Gesellschaft, one of the first questions discussed Avas the formation of a uniform nomenclature. After much Avork and expense, His droAV up ^lie official report of the international commission, in 1895 : it is another standard which the leading teachers and authors have agreed to folloAV. The ncAV nomenclature is a comproniise ; it is not radical, but it has reduced the numl)er of anatomical names, including synonyms, by al)Out eighty per cent. It Avill not be .difficult for English-speaking anatomists to accept this terminology, for it diifers less from ours than from that of any other language.
If we consider the great aninnnt of Avork His did upon the form and
150 Wilhelm His
position of the organs, upon the general morphology and structure of the brain, upon embryology, histology and histogenesis, and upon anatomical terminology, it may safely be said that there is barely a page in the broad field of anatomy from the ovum to the adult in wliich his work does not appear.
Early in his career. His showed much interest in physical anthropology as we see by the great monograph he and Eiitemeyer published on Swiss skulls. But his time was occupied in so many other directions that it was impossible for him to continue in this kind of work with the inadequate assistance he had at Basel. However, some thirty years later, he had an opportunity to open up a new line of research in anthropology. A skeleton, presumably that of Bach, had been found and His was asked to give an opinion regarding it. It was known that Bach had been buried in an oak coffin near a certain corner of a church-yard. Here among others was found the skeleton of an elderly man (Bach died at the age of sixtyfive) in an oak coffin. The skull was found to be peculiar and in it the anatomist could discern the features of the portraits of Bach. His at once proceeded to measure the thicknesses of the soft parts over the bony prominences of the heads of cadavers and found that in average bodies these thicknesses are constant, varying only with age and sex. He next drew averages from the measurements taken from cadavers of elderly men of fair development, and, with these, Seffner, the sculptor, constructed a clay bust on the skull in question. It was found that the reconstructed bust presented all of the characteristics of Bach even more pronouncedly than do his portraits. The commission that had the matter in charge decided that the skeleton in question was undoubtedly that of Bach. As such, it was reinterred. The musical world through His's studies now has a bust of the great composer.
These results gave His the greatest aesthetic pleasure, for they meant a new victory." From, this time on he was greatly interested in inductive anatomy and when I began my career at the Johns Hopkins, he gave me every possible encouragement in this direction.* He often wrote and he often talked about statistical work, but little did I realize the difficulties of it until we began to tabulate a peripheral nervous system from a very large number of individual records. It became apparent from our records that variations are more common in certain parts of the body than in others and this result interested His very much."
His was never inclined to develop a school nor was he anxious to have pupils. When I knocked at his door at first I was turned away, but after appearing a number of times, was finally accepted. When he set a problem, it was concisely stated; he outlined the general plan by which
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it was to be solved. All of the details were left to the pupil and it annoyed him to be consulted regarding them. He desired that the pupil should have full freedom to work out his own solution and aided him mainly through severe criticism. Specimens and drawings of them which were not analyzed did not appeal to him and he objected much to pictures which appeared to represent a mass of " baked tissue." Through reactions, either with coloring matter or with some destructive reagents, or by means of reconstructions, tissues must be emphasized and we see this characteristic in the illustrations of all of his publications. A His drawing can always be recognized even if it appears without his name attached to it.
His was unwilling to give his own problems to pupils and though later in life he advocated the establishment of research institutes, it is not altogether clear how he reconciled the one attitude with the other. But the institute is rather for routine research and for a discussion of work by leading investigators who consequently formulate problems to be solved by organized united effort; it is not intended to dwarf individual effort in any respect. His was unwilling to write papers for his pupils and the manuscripts they placed Before him were improved only through erasure, for he excluded all doubtful evidence and irrelevant matter. " Your paper will be read by a few specialists, and they do not want a treatise on the science," he would say, and this criticism coming to a pupil during the same years that silence on such subjects and encouragement came from Ludwig, proved to be of the greatest value.
His did not have much power to extend his own private work through his assistants and pupils; they were always given the greatest freedom for it was against his nature to enslave them to the least degree. Nor did he possess the patience of a Liebig or a Ludwig in training others to follow in his path. Further, he did not find that successful research can often be stimulated by example, although men, and scientists too, are imitative. He often told me that the acceptance of a discovery is frequently postponed by numerous "confirmatory" publications which are filled with so much crude and irrelevant matter that the real point is buried again; and that the desire of authors to attract attention often induces them to invent names and write much, thereby making the answer to a question more obscure than it was before.
Several visits to the Zoological Station at Naples made a profound impression upon His for it showed him what organization can do for research, and in 1886 he published a paper on the necessity of research institutes. In this he pointed out that the function of such institutes is (1) to solve problems which exceed the power of one man to settle.
153 Williolm His
aiul {2) to c'olloet, classify and conserve all the material relating to such problems. After a whole life-time has been occn'[3ie(l in collecting material, it seems a great pity that so much work should be lost at the death of the collector; could such material and such lives be made available for the solution of the great problems by an institute or institnte of institutes (as is the case in astronomy) more progress might be made. In the foundation of such an institute the many details of embryology and neurology shonld first be surveyed ; were the field divided, this could be done quickly. Problems would have to be formulated, and a common nomenclature and standard of measurements agreed upon. In no case should individual effort be hampered. Conferences would be necessary from time to time to compare, to criticise results and to formulate new problems and new plans for their solution, thus aiding all with the best, as should be the case in ideal scientific investigation. The underlying thought is to extend the power of able investigators through the whole science without dwarfing in any way individual effort; in this way the best qualities of all could be made to serve the progress of science.^" The Anatomische Gesellschaft was founded with this as one of its objects in view ; it naturally resulted as we have seen in the casting of a imif orm nomenclature. Two great steps had thus been taken and His lived to see the beginning of a third.
The tendency in the world during all of His's life was more and more towards specialization and organization in science, a movement which gradually became international. An index of this tendency may be seen in the organization of the International Association of Academics and through its machinery. His was able to launch his favorite scheme.
Unlike many promoters of science. His was not an impressario and consequently the learned world had full faith in him. What he advocated always was the advancement of science. Tha possibility of personal gain was excluded from his thoughts as is shown by his attitude towards endowments, especially the N"obcl Fund." He maintained all along that a research fund must fall into the right hands if it is to benefit science and that it was of positive injury to science when in the hands of impressarios."
His proposed at the first meeting of the International Association of Academies, held in Paris in 1901, that a commission be appointed for the promotion of the stndv of human embryolos^y and another for the study of the anatomy of the brain. The Association agreed to the appointment of the latter, at the same time recommending that for the present, hirman embryology should be taken up by the anatomical societies. Later, upon the recommendation of the Saxon Academy, the Eoyal
Franklin P. :\rall 153
Society of London appointed a jSTeiirologieal Commission of seven members with His as chairman. The Commission liad been established and three bulletins had been, published preparatory to the first general meeting, but His died before the meeting convened. His plan ^yill live, for it has taken deep root and has the approval of leading anatomists of the world.^"
The life of His was a life of work, and his energy, industry and endurance were so great that he hardly knew the meaning of leisure. He possessed the qualities of a courageous leader, but lacked the magnetism that compels many admirers and followers. He was a daring and origi-nal investigator, possessing great technical ability and artistic feeling; he was fearless and honorable in controversy and knew no compromise. He was a great character, true to his family, true to his friends and true to science.^
Through His, another milestone has been set for anatomy. Through him the great mother science has given birth to a new science, histogenesis. His career is marked by a monument of neurological research which is unique. His's life was that of the ideal scholar. During youth he was strengthened through his own efforts, directed by great masters. During middle age, he won many victories for anatomy, improving the science in all its parts. In old age, he completed and rounded up his work, leaving a great legacy to his survivors, no small part of which consists of wise plans for future work.
REFERENCES AND EXTRACTS FROM LETTERS.
^ Wilhelm His was born in Basel on July 9, 1831. His father, Edward His, was a son of the Swiss statesman, Peter Ochs. In 1818, when Edward Ochs became engaged to be married to Anna La Roche, he assumed the name of His, the maiden name of his father's mother. He did this with the consent of Peter Ochs in order to remove the ridicule of his name from which he had imdoubtedly suffered. After graduating from the Gymnasium, His studied medicine in Basel, Bern, Berlin, Wiirzburg, Prague and Vienna, returning to Basel to take his doctor's degree, in 1854. Later, he studied in Paris, returning to Basel as " Privatdocent " in 1856. In the summer of 1857 he was again in Berlin and in the autumn he was appointed Professor of Anatomy and Physiology in Basel. In 1872 he accepted the call to the chair of anatomy at Leipzig, where he died May 1, 1904.
A charming account of His's early life is given by him in his Lebenserinnerungen (als Manuskript gedruckt), Leipzig, December, 1903. See also W. Spalteholz, Zum siebzigjiiJirigen Geburtstag von Wilhelm His, Miinchener Medizinischen Wochenschrift, No. 28, 1001; and Wilhelm His, ibid, No. 22, lOO'f. Rudolph Fick, Wilhelm His. Anatomischer Anzeiger, Vol. 26, 1904- B. Rawitz, W. His, Naturicissenschaftliche Rundschau, No. 24, 1904.
15-t Wilhelm His
Francis Dixon, Prof. Wilhelm His, Journal of Anatomy and Physiology, Vol. 3S, 190.'/. W. Waldeykk, Wilhelm His, Sein Leben und Wirken, Deutsche Medizinische Wocheuschrift, Nos. 39, 40 and J/l, 1904. J- Kollmann, Wilhelm His, Worte der Erinnerung. Yerhandl. der Nattir. Gesell. in Basel, Bd. 15, 1904. J, Maechand, Wilhelm His, Is'ekrolog, Bericht. d. K. s. Gesell. d. Wiss., Nov. 14, 1904.
Ich hatte in Berlin bei Johannes Miiller und bei Remak tiefe Anregungen erfahren, im iibrigen aber einen nur maszigen Schatz von geordneten Kenntnissen eingespeichert. Es hatte mir an sicherer Fiihrung gefehlt: unter den Medizinern hatte ich keine Gleichgesinnten gefunden, und mein eigentlicher Freundeskreis bestand aus Landsleuten, meistens Theologen und Juristen. Schone Gelegenheiten, mir griindlichere physikalische und chemische Kenntnisse zu erwerben, habe ich verpasst und statt dessen einige recht sterile medizinische Vorlesungen abgesessen. Auch die historischen Vorlesungen von Ranlce und die geographischen von Ritter, von denen meine Freunde soviel Interessantes zu erzahlen wussten, hatte ich ohne Opfer an Fachbildung besuchen konnen. — Lehenserinnerungen, p. 28.
^ An jene Zeit absoluter Arbeitsfreiheit habe ich seitdem oft mit Sehnsucht zuriickgedacht. Allerdings bot sie auch die Gefahren des Sichverlierens, so habe ich einmal acht Tage lang an der Herstellung eines Glasblasertisches gezimmert, bin aber dann, nach dessen notdiirftiger Vollendung, von einem gehorigen Katzenjammer iiber die sinnlos vergeudete Zeit heimgesucht worden. Im Grund habe ich aber in spateren Jahren die Erfahrung gemacht, dass fiir den Fortgang eigener geistiger Arbeit die Belastung mit einem maszigen Pflichtenpensum vorteilhafter ist als die absolute Freiheit, und insbesondere habe ich oftmals beim Beginn ersehnter Ferien gefunden, dass zugleich mit dem Eintritt freier Zeitverfiigung eine Erschlaffung der geistigen Spannkraft sich einstellte, die erst allmahlich und durch Zwang sich wieder iiberwinden liess. Das Gefahrlichste ist hierbei das Abwartenwollen von Arbeitsstimmungen; solche wirklich fruchtbare Stimmungen konnen ja zeitweise unverhofft einbrechen, viel haufiger aber sind sie nur dadurch erreichbar, dass man sich erst gewaltsam durch ode und anscheinend unfruchtbare Anfange hindurch kampft. Hat man einmal sein Arbeitsziel klar vor Augen, dann lernt man auch bald die kleinsten Zeitabfalle des sonstigen Tagewerkes ergiebig zunutze zu Ziehen. — Lebenserinnerungen, p. 48.
Die meisten jungen Manner mussen nach Abschluss ihrer Universitatszeit eine Periode des Missbehagens durchmachen, bis es ihnen gelungen ist ihre idealen Bestrebungen in eine Thatigkeit fiir's Leben umzusetzen. — From a letter of March 20, 1887.
^ Es ist ein schweres, dem seiner Natur getreu bleibenden Forscher auferlegtes Gestandniss, dass die letzten Ziele, fiir deren Verfolgung er seine ganze Kraft einsetzt, hier, wie auf alien Gebieten der Forschung, in um so entlegenere Feme riicken, je weiter er auf dem in ihrer Richtung fiihrenden Wege voranschreitet. In der kraftigenden Arbeit selbst, im Bewusstsein sicheren Voranschreitens und in den reichen, am Wege ihn erwartenden Priichten findet er den vollen Ersatz fiir alle geiibte Entsagung. — Vnsere Eorperform, 1874, p. 215.
' Ist es ja doch die Gabe geistvoller Naturen, dass sie, auch bei beschrankten Hiilfsmitteln materieller Erkenntniss, Beziehungen zuahnen und in ihrem
Franklin V. Mall 155
Zusammenhang zu durchschauen vermOgen, die Anderen bei weit reicherem Material nur stiickweise zuganglich sind, und dass sie selbst im Irrthum oft Grcsichtspunkte eroffnen, die der langsam und miihselig vordringenden Einzelnforschung als Wegweiser fiir die Richtung ihres Ganges dienen konnen. — Die Hiiute und Hohlen des Korpers (1865), Archiv fiir Anatomie, 1903, p. 369.
' Soil ich zum Schluss noch einmal versuchen, die histologischen Rollen der Keimschichten zu sondern, so komme ich zu folgender Aufstellung: Der Epiblast liefert das Nervengewebe und die Horngewebe. Der Hypoblast gliedert sich in
den embryonalen Mesoblast, die gemeinsame Anlage fiir das quergestreifte und glatte Muskelgewebe, fiir die Epithelien des Genitalapparates und fiir die embryonalen Bindesubstanzen. das ausserembryonale Mesenchym,
den Angioblast, die Anlage des Blutes und der Blutcapillaren, das Endoderm, die Anlage der Epithelien und Driisen des Eingeweiderohres. Der Lecithoblast, da, wo er zur Entwickelung kommt, bildet einen Theil des Hypoblast.
Das alte Rathsel erweist sich zur Zeit immer noch ungelost: noch konnen wir nicht sagen, weshalb ein Theil der gegebenen Anlagen zu Bindesubstanzen wird, und was die Blut- und Capillarzellen bestimmt, so friihzeitig und so scharf sich von ihren scheinbar so nahen Verwandten, den Zellen der Bindesubstanzen, zu scheiden. — Lecithoblast und Angioblast der Wirbelthiere, Abhandl. d. K. Sdch. Gesellschft. d. Wiss., Bd. 26, 1900, p. 326.
Ich schliesse diesen in jeder Hinsicht fragmentarischen Aufsatz iiber die intramedullaren Faserbahnen des Gehirns mit der Bemerkung, dass er zur Zeit nicht viel mehr zu bieten vermag, als ein Arbeitsprogram fiir kommende detailliertere Forschungen. Noch sind wir eben in Erkenntniss dieser Dinge in den allerersten Anfangen, und es bedarf hier, wie anderwarts, zaher Arbeit bis die Entwicklungsgeschichte des Gehirns nach ihren verschiedenen Richtungen hin befriedigend kann klar gelegt werden. Zur Zeit kann ich nur angeben, wo diese Arbeit einzusetzen hat. Friiher oder spater wird man auf diesem Gebiet zum System organisierter gemeinsamer Arbeit iiberzugehen haben. — Die Entwickelung des Menschlichen Gehirns, Leipzig, 1904, p. 175.
^ Im Leben unsrer Universitaten macht sich bei aller anscheinenden Fortdauer ihrer Leistungen, und auch bei ununterbrochenem Ersatz abgehender Krafte durch neu eintretende, eine ganz bestimmte Periodicitat der Entwicklung geltend. Fiir die Gesammtuniversitat und fiir die Facultaten folgen auf Perioden geistigen Aufschwunges solche der Ruhe und des Riickgangs. Aeussere und innere Bedingungen wirken dabei zusammen und es ist nicht immer leicht, deren Ineinandergreifen zu verstehen. Eine Grundbedingung muss aber stets erfiillt sein, falls eine Korperschaft bliihen soil. Die Korperschaft muss kraftige und zielbewusste Fiihrer besitzen, welche deren Geist in bestimmte Bahnen zu lenken und unter ihren Gliedern die Gemeinsamkeit des Strebens zu sichern wissen.
Solch ein fiihrender Geist ist in unsrer Facultat wahrend mancher Jahrzehnte Ernst Heinrich Weber gewesen, welcher vom Jahr 1821 ab die Pro11
156 Wilhelm His
fessur der Anatomic und spaterhin (von 1841 ab) noch die der Physiologie bekleidet hat. Die Spuren seiner machtigen Personlichkeit haben sich als bleibende erhalten nicht nur in den Acten unserer Facultat, sondern noch tiefer begriindet in denen der Wissenschaften, die er vertreten und die er um ausgedehnte neue Gebiete bereichert hat.
Bis zum Jahre 1865 hat Ernst Heinrich Weber, von seinem Bruder Eduard unterstiitzt, die Doppellast der beiden ausgedehnten Facher getragen. Dann aber, als die Neuschopfung einer physiologischen Anstalt in Aussicht genommen wurde, und dadurch neue Verpflichtungen an den Lehrer der Physiologie herantreten sollten, zog sich der alternde Gelehrte auf seine urspriingliche Anatomieprofessur zuriick, und es ist nun auf Ostern 1865 (unter dem Dekanat Wunderlichs) die Berufung.von Karl Ludwig als Professor der Physiologie und Director des neu zu begriindenden physiologischen Instituts erfolgt.
Die Initiative zu diesen Neuerungen ist von der koniglichen Regierung ausgegangen. Im Sinn ihres hohen Monarchen, des Konigs Johann, batten sich die einsichtigen Leiter des Ministeriums, Hr. Staatsminister v. Falkenstein und Hr. Geh. Rath Dr. Hiibel, die Aufgabe gestellt, die Universitat Leipzig mit alien aufwendbaren Mitteln zu neuem Glanze zu erheben. Die physiologische Anstalt wurde als das erste Glied einer Reihe von Neuschopfungen geplant, deren Endziel die Umgestaltung des gesammten naturwissenschaftlichen und medizinischen Unterrichts sein sollte. In der Wahl von Professor Ludwig hat die k. Regierung eine begonders gliickliche Hand bewiesen, denn sie gewann an ihm fiir ihre ferneren Entscheidungen einen vermoge seiner Einsicht und seiner organisatorischen Kraft ganz besonders befahigten Rathgeber. Ludwig's Einfluss hat sich wahrend der v. Falkenstein'schen Periode weit iiber das medizinische Facultatsgebiet hinaus erstreckt, und seiner Anregung sind von den bedeutendsten Berufungen jener Zeit zu verdanken gewesen. Spater, nachdem einmal die Organisation naturwissenschaftlichen Unterrichts fiir Leipzig erreicht und nachdem auch das Cultusministerium in andere Hande iibergegangen war, hat sich Ludwig auf sein engeres Arbeitsgebiet zuriickgezogen. Was er aber auf diesem Gebiete geleistet hat, das hat den Ruhm der Leipziger Universitat bald durch alle Lander verbreitet. — Karl Ludwig und Karl Thiersch, Beilage, AUgemeinen Zeitung, Nr. 164. 19 JuU, Milnchen, 1895.
" Ich danke Ihnen fiir den inhaltsreichen Aufsatz iiber die Darmentwicklung, die in der mir iiberreichten Jubilaumsschrift thatreich hervortritt. Alle diese Bezeugungen haben mich herzlich gefreut. Dauernd wird die Befriedigung iiber Ihre Arbeit sein, die ein bis jetzt so wenig klarer Gebiet endgultig in's Reine bringt. Was ja bei den meisten unserer bishorigen entwickelungsgeschichtlichen Vorstellungen fehlt, das ist die Beobachtunggrundlage fiir die Uebergangsphasen aus den friih embryonalen in die foetalen und von da in die ausgebildeten Stufen. Fiir den Darm haben Sie nunmehr die ganze Kette vom Anfang bis zum Ende zusammengefiigt und das halte ich fiir einen grossen Fortschritt. — Froin a letter of Octoher 29, 1897.
" So weit ich iiber solche freie Augenblicke verfiige, widme ich sie noch meiner alten unglticklichen Liebe den Knochenfischen. Ich habe seit dreissig Jahren schon unendlich viel Zeit damit verloren. sie sind ein methodisch
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sehr schwer zii bearbeltendes und launisches Material, und doch locken mich die uniiberwimdenen Scliwierigkeiten und offenen Fragen immer wieder zu neuen Anlaufen. — From a letter of December 25, 1898.
'-Wie bei der wissenschaftlichen Arbeit, so tritt aucli bei unserer heutigen Lehrweise der Respect vor der Thatsaclie in den Vordergrund, und wir bemiiben uns in erster Linie auch unsere Scbiiler dazu zii erziehen. Beim naturwissenschaftlichen und somit auch beim medizinischen Unterriclit ist unsere Sorge, dem Anfanger die Kunst unbefangener Beobachtung beizubringen. Wir halten ihn an, die Sinneswalirnehmungen scharf zu trennen von den daran sich ankniipfenden Schlussfolgerungen, wir warnen ihn vor de^ Beeinfliissung durch vorgefasste Meinungen und belehren ihn iiber die Taiischungsquellen, die in unsern eigenen Sinnen sowie in unsern besten Apparaten enthalten sind. Vor allem aber suchen wir den Schiiler dazu zu bringen, dass er sich angewohnt, das Gebiet eigener Brfahrungen selbstandig zu klaren Begriffen zu verarbeiten. So klein Anfangs das Capital an solch eigenem Erwerb sein mag, so gewahrt es dem Besitzer doch bald das Gefiihl einer bestimmten geistigen Freiheit und Unabhangigkeit, das Gefiihl des tiichtigen Menschen.
Was hat nun aber diese, vorwiegend auf Scharfung der Kritik hinstrebende Form der Schulung mit der Spaltung der Lehrfacher zu thun? Der Zusammenhang ist leicht nachzuweisen. So lange es sich um blosse Ueberlieferung systematisch geordneter Begriffe in dogmatischer Form handelt, ist ein fleissiger Gelehrter mit Hilfe der nothigen Lehrbiicher, der duces Arnemann, Gaubius und Metzgerus im Stande, ein ausgedehntes Gebiet als Lehrer zu umspannen, ja selbst vom Ueberspringen von einem Fache auf ein anderes, mehr order minder entlegenes, wird ihn kein inneres Hinderniss abhalten. Wenn wir horen, dass in einem friihern Jahrhundert die Lehrfacher innerhalb der philosophischen Facultat jedes Jahr frisch ausgelost wurden und dass auch nach Beseitigung dieses Modus noch die Verpflichtung bestand, dass ein jedes Facultatsmitglied alien Fachern gerecht sein musste, so ist diese heutzutage undenkbare Einrichtung dadurch verstandlich, dass in jenen Perioden die Bedeutung der allgemeinen Gelehrtenbildung iiber diejenige der Fachbildung weit iiberwog, wahrend wir nunmehr auf dem entgegengesetzten Standpunkt stehen. Sowie verlangt wird, dass der Lehrer die wissenschaftlichen Ergebnisse seiner Disciplin anstatt bios in dogmatischer Form, auch nach ihrer Begriindung dem Schiiler mittheile, so fallt eine Hauptseite des Unterrichts in die wissenschaftliche Methodik. — Ueber EntwickelungsverMiltnisse des Akademischen Unterrichts, Rektoratsrede, Leipzig, October 31, 1882, p. 33.
" Ludwig's Forscherwaffen waren eine ungemain scharfe Analyse der ihm vorliegenden Natui'erscheinungen, eine stets klare Fragestellung und eine absolute Sicherheit seiner Methodik. Dabei verfiigte er aber auch iiber eine ausreichende Dosis jenes Findersinnes,- ohne den in Erforschung der lebenden Natur selbst die klarsten Denker oft machtlos bleiben. Die Natur lasst sich nicht immer mit Logik zwingen, ihre Wege sind nicht selten versteckt, und sie enthiillen sich nur dem, der sich in ausdauernder und treuer Beobachtung den Blick auch fiir deren unscheinbare Spuren gescharft hat. Die unmittelbare Liebe zur sinnlichen Beobachtung hat aber Ludwig im hohen Maasse
158 Wilhelm His
besessen, und fiir ihn ist ein gelungenes Praparat Oder ein schlagender Versuch stets Gegenstand eigentlich asthetischen Genusses gewesen. — Carl LudwiG, Oediichtnissrede, Bericht, d. K. s. Gesell. d. Wiss., November 14, 1895, p. 6.
" Ihre Bestrebungen eine inductive anatomische Unterrichtsmethode zur schaffen, interessiren mich sehr lebhaft. Wenn es Ihnen mit fiinfzig Schiilern gelingt, zum Ziel zu kommen, so ist dies jedenfalls eine anerkennungswerthe Leistung. Vor Kurzem publicirte der bel^annte, Dr. Schweninger, einige Aufsatze liber die Erziehung von Medizinern, worin er iiberhaubt das Prapariren verwarf und meinte, man soil die Anatomie gleich am Lebenden vornehmen, die Studenten durch Percussion, u. s. w. die Organe auf den Korper zeichnen lassen, u. s. w. Unsere Medizinererziehung ist zwar krank an zu vielem Auswendiglernen von Bucherweisheit und gewiss konnte auch in der Anatomie dem Studenten manches osteologisches Detail erlassen werden. Aber abgesehn davon, ist ja der Prapariersaal eine so wichtige Schule der Beobachtung und der Handfertigkeit, dass eine grosse Beschranktheit dazu gehort, das anatomische Prapariren beseitigen zu wollen. — From a letter of December 31, 1896.
" His's influence in America has been great, greater than in any other country, even Germany. He took a lively interest in our whole development, in the development of our universities, scientific societies and journals. He was much pleased with the numbers of the American Journal of Anatomy, and appreciated above all the leading article by Bardeen and Lewis. " Auch dariiber habe ich mich gefreut dass Sie mit so viele Andere zusammen arbeiten." He always approved of cooperation.
'" Was Sie mir damals von " Carnegie Institution," geschrieben haben, muss uns, diesseits des atlantischen Oceans Lebende mit innigem Neid erfiillen. Es ist indessen keine Frage, wir sind in eine Periode eingetreten, in der die zu leistende Arbeitssumme immer grosser und die Anspriiche an Reichlichkeit des Materiales und die Pracision seiner Durcharbeitung immer strenger werden und da hilft eben schliesslich nur ein wissenschaftlicher Grossbetrieb mit guter Organisation. Noch haben wir in Deutschland bei aller Arbeit ein zu planloses Durcheinanderrogen, und zu viel Kraft geht in personlicher Reibung verloren. Der Ehrgeiz ist ein wichtiger Antrieb zur Arbeit, aber anderseits fiihrt er auch vielfach dahin, dass die Arbeiter anstatt sich zu unterstiitzen, sich gegenseitig herabzumindern suchen. . . . Noch vor zehn Jahren hatte mir die Organisation eines grosseren rein wissenschaftlichen Institutes, die grosste Freude gemacht. Mit zwei und siebenzig Jahren weiss man aber, dass die Arbeitszeit nur noch knapp zugemessen ist, ganz abgesehen davon, dass die Arbeit viel langsamer von der Hand geht. — From a letter of March 17, 1903.
" Ich hatte im vorigen Sommer einen Anlauf genommen, um die Begriindung besonderer entwickelungsgeschichtlichen Institute und Gehirninstitute in Anregung zu bringen, aber bis jetzt habe ich noch nicht Viel erreicht. Es fehlen uns in Deutschland und in Europa jene Milliardare die bei Ihnen so fix bei der Hand sind, wenn grosse Schopfungen fundirt werden sollen. Das immense Capital, dass der Ingenieur Nobel fiir wissenschaftlichen Zwecke vermacht hat, ist dadurch nutzlos, dass er die Vertheilung der Zinsen in Form von Preisen
Franklin P. Mall 159
bestimmt hat. Da diese Preise jedes Jahr vertheilt werden sollen so wird, wie ich fiirclite, die Zutheilung bald zu Parteisache werden und viel Unfrieden herbei fiihren. — From a letter of December 31, 1902.
" Wird durch solche Preise die wissenschaftliche Arbeit wirklich gefordert?" Ich glaube, man kann diese Frage ruhig verneinen: kein aus innerem Antrieb arbeitender Forscher wird dadurch, dass ihm das Schicksal eine grossere Summe Geldes in den Schooss wirft, ein Anderer werden. Er wird eben iiber die Ehre des Preises und iiber den empfangenen Betrag sich freuen, im Uebrigen aber seinen Gang weiter gehen, als ob Nichts geschehen ware. Und wer den Preis nicht bekommt, wird nicht anders verfahren. Hochstens liegt fiir den letzteren, wenn er nicht edel veranlagt ist, die Versuchung vor, dem begiinstigten Collegen, oder denen, die iiber den Preis zu bestimmen hatten, unfreundliche Gefiihle nachzutragen. — Ueber wissenschaftliche Stiftungen, Bericht. d. K. s. Gesell. d. Wiss., 1901, p. 434.
" Sie haben an ihren neueren amerilianischen Universitaten einen liraftigen Nervus rerum, und wenn reiche Hilfsmittel in die richtigen Bahnen kommen, so lasst sich ja Vieles in verhaltnissmassig kurzer Zeit erreichen. Die Hauptsache bleibt immer dass die Fiihrung solch fortschreitender Bewegungen in den Handen von Mannern bleibt, die wissen, woraus es bei geistigen Schopfungen ankommt. Es ist immer befriedigender, vollig Neues zu schaffen, als am Alten herumzuflicken. Letzters Schicksal fallt uns in Europa nun allzu oft zu. Augenblicklich soil wieder an unsern Examenreglementen geflickt werden, eine Arbeit die nur wenig Freude bringt, da der Ballast alter Vorurtheile und Wiederstande nicht iiber Bord geworfen werden kann. — From a letter of April 22, 1S99.
•» Genebal Outline of the Development of His's Institute foe the Study of
THE Brain. A. — Proposition to the International Association of Academies, Paris, April 20, 1901. Die Internationale Association der Akademien moge eine Fachcommission aufstellen zur Berathung der Mittel und Wege, wie auf den Gebieten, einestheils der menschlichen und thierischen Entwicklungsgeschichte, anderntheils der Hirnanatomie eine nach einheitlichen Grundsatzen erfolgende Sammlung, Verarbeitung und allgemeine Nutzbarmachung von sicherem Beobachtungsmaterial erreicht werden kann.
B. — Decision of the Association of Academies.
1. Die Berathung der auf menschliche und thierische Entwicklungsgeschichte beziiglichen Abschnitte des Antrages ist vorerst den betreffenden Fachvereinen (den anatomischen Gesellschaften) zu iiberlassen.
2. Dagegen setzt die Internationale Association der Akademien eine Specialcommission nieder, die eine nach einheitlichen Grundsatzen erfolgende Durchforschung, Sammlung und allgemeine Nutzbarmachung des auf Gehirnanatomie beziiglichen Materiales zu berathen hat. Die Commission hat insbesondere die Schaffung eines internationalen Systemes von Centralinstituten in Erwagung zu Ziehen, in denen die Methoden der Forschung entwickelt, das vorhandene Beooachtungsmaterial aufgespeichert und der allgemeinen Benutzung der dabei interessirten Gelehrten zuganglich gemacht werden. — An
160 Wilhelm ITis
trag der Kon. Sach. Ges. an die Royal Society of London, Ber. d. K. s. Oes. d. Wiss., February, 1902. C. — Objects of the Institute.
1. Die Aufspeicherung und Zuganglichmachung von wissenschaftlichem (normalem) Material an Praparaten, Modellen, Photogrammen, Zeichnungen u. s. w.
2. Die technische Hilfeleistung bei wissenschaftlichen Untersuchungen.
3. Die Aufbewahrung von wertvollem experimentellphysiologischem und pathologischem, bereits bearbeitetem Oder noch zu bearbeitendem Material.
4. Die Bewaltigung grosserer, iiber die Krafte einzelner hinausgehender Aufgaben, soweit solche zur Kooperation sich eignen. — Antrag der von der Internationalen Association der Akademien Niedergesetzter Commission fur Hirnforschung der Generalversammlung der Association in London zum 25 Mai, 1904, vorgelegt, Leipzig, 1904.
D. — Organisation of the Institute.
1. Arbeitsfeld und Arbeitsweise bleiben jedem einzelnen Institute iiberlassen. Es sollen jedoch angestrebt werden:
a. Eine einheitliche Nomenklatur.
b. Verwendung eines einheitlicben Masses und Gewichtes.
2. Alljahrlich statten die Institute der Centralkommission einen Bericht iiber ibre Thatigkeit ab. Dabei sollen der Bestand und die Zugange an Druckwerken, Abbildungen, Modellen und Praparaten mitgetheilt werdea.
3. Die Institute sind gebalten ihre Arbeitsmaterialien und die Sammlungen ihrer Praparate einander unter sich, sowie den derselben bediirftigen Forschern nach Moglicbkeit zuganglich zu macben. — Bericht, etc., Bericht. d. K. s. Gesell. (Z. Viss., June 8, 1903.
D. — Sections.
1. Die systematische Anatomie des menschlichen Centralnerven-systems, einschlieszlich der Anthropologie.
2. Die vergleichende Anatomie.
3. Die histologische Forschung.
4. Die entwickelungsgeschichtliche Forschung.
5. Die Physiologie, einschliesslich der physiologischen Psychologic.
6. Die pathologische Anatomie, experimentelle Pathologie und Teratologie.
7. Die klinische Forschung. — Entwerf. Motiv zu den Antragen, etc., Leipzig, January 3, 1904.
F. — Special Committees.
1. Waldeyer, Cunningham, Mall, Manouvrier, Zuckerkandl.
2. Ehlers, Edinger, Giard, Guldberg, Elliot Smith.
3. Golgi, Ramon y Cajal, Dogiel, van Gehuchten, Retzius.
4. His, Bechterew, v. Kolliker, v. Lenhossek, Minot.
5. H. Munk, Horsley, Luciani, Mosso, Sherrington.
6. Obersteiner, Dejerine, Monakow, Langley, Weigert.
7. Flechsig, Hentschen, Ferrier, Lannelongue, Reymond. — Protokoll von der Internationalen Association der Akademien Niedergesetzten Centralkommission filr Gehirnforschung, January 11, 1904. Bericht. d. K. S. Gesell. d. Wiss., 1904.
Franklin P. Mall 161
" Es that mir wohl aiis Ihrem Brief, wie aus vielen Andern, die ich bekomnien habe, zu sehen, wie mein Mann nicht nur durcli seine Wissenschaft, sondern noch mehr durch sein Leben und seinen Karakter seinen Schiilern etwas Gutes erwiesen hat. — From a letter from Frau Professor His of June 8, 1904.
Ich bin mit diesen Aufzeichnung an einen Punkte angelangt, wo ich sie abschliessen kann. In reichem Wechsel sind mir beim Niederschreiben obiger Blatter Bilder vor Augen getreten von einer Fiille von treflaichen und von hervorragenden Menschen, mit denen ich im Laufe meiner Entwiclvlungsjahre in Beziehung_ getreten bin. Gar manche Namen hatte ich der Schar noch beifiigen konnen. Von alien diesen Menschen habe ich gelernt oder sonstwie Gutes empfangen. Die weit iiberwiegende Mehrzahl derselben sind langst dahingeschieden, alien aber bewahre ich ein dankbares Andenken. Mogen andere dereinst auch von mir dasselbe sagen konnen. — Lehenserinnerungen.
THE DEVELOPMENT OF THE THOEACIC VERTEBRA IN
MAN.
BY
CHARLES R. BARDEEN, Professor of Anatomy, the University of Wisconsin, Madison, Wisconsin.
With 7 Plates.
There is a somewhat extensive literature dealing with the development of the spinal column in various vertebrates. The chief stages in its differentiation are fairly well determined. Special attention has been given to the early development in the lower vertebrates. The recent literature on this subject up to 1897 has been reviewed by Gaupp, 97.* Somewhat less attention has been devoted to the mammals. To Froriep, 86, is due a valuable account of the development of the cervical vertebrae in the cow, and to Weiss, 01, an important description of the development of the thoracic and cervical vertebrae in the white rat.
We shall not attempt to enter here into a description of the early stages of differentiation in the spinal axis; that is of the period covering the formation of the chorda dorsalis and of axial and peripheral mesoblast, the differentiation of primitive segments, and the origin of the axial mesenchyme. This period in the human embryo has been well treated by Kollmann, 91, and some account of it has previously been given in this Journal (Bardeen and Lewis, 01). We shall therefore proceed at once to a consideration of vertebral differentiation in the axial mesenchyme.
Vertebral development in the embryo may be divided into three overlapping periods: a membranous or blastemal, a chondrogenous, and an osseogenous."
'Among more recent papers may be mentioned, those of Baldus, 01; Hay, 97; Kapelkin, 00; Manner, 99; Mannich, 02; Ridewood, 01; and Schauinsland, 03.
^ In the text books the first of these periods is usually called the precartilage, prochondral, or YorknorprA stage, but the condensed tissue from which the skeletal parts are derived gives rise not only to cartilage but also to perichondrium and to ligaments. Recognizing this fact, Schomburg, 00, has American Jouknal of Anatomy.- — Vol. IV.
164 Development of Tlioracic Ycrtcbne in Man
The Blastemal Period.
The division of the axial mesenchyme into segments, sclerotomes, which correspond to the myotomes and spinal ganglia, is marked at an early stage by intersegmental arteries. Schultze, 96, has shown that the segmental differentiation of the axial mesenchyme extends into the region dorsal to the spinal cord. Ventrally it does not, however, extend quite to the chorda dorsalis. Fig. 1, Plate I, illustrates the conditions existing in the thoracic region of man at this period.
V. Ebner, 88, found in the embryos of several vertebrates a fissure which divides each sclerotome into an anterior and a posterior portion. Schultze, in 1896, showed, that in selachians and reptiles this fissure is represented from the time of its formation by a diverticulum which communicates with the myoccel. In birds the diverticulum arises secondarily and later becomes fused with the myocoel, and in mammals it arises after the myocoel has disappeared.
In man the fissure becomes distinct in the thoracic region at about the end of the third week of development (Fig. 2, Plate 1).' At this period the median surface of each myotome has become converted into muscle fibres (Fig. 2, Myo.). At the same time the mesenchyme in the posterolateral region of each sclerotome has become condensed so that it appears, in a stained section, dark when compared with that of the anterior half (Fig. 2). At the lateral margin of the anterior halves of the sclerotomes the spinal nerves expend out toward the thoracic wall (Fig. 2, 8p.N.). The division between the sclerotomes is still marked by the intersegmental arteries (Fig. 2). About the chorda dorsalis the cells of the axial mesenchyme become densely grouped into a perichordal sheath. The long axes of the cells lie parallel with the chorda (Fig. 2, Pch. 8.).
The condensation of tissue which distinguishes the posterior sclerotome half begins, as mentioned above, in the posterior lateral area of each
called the condensed-tissue stage, the mesenchymal period, and restricted the term Vorknorpel to the earlier stages of the formation of cartilage. The term " blastemal " is now-a-days commonly used to designate a mass of mesenchymal tissue from which organs are to be differentiated, and is applied to the tissue of the limb-bud before differentiation has commenced. It seems to me that it would be well to extend this term to the structures first differentiated in the limb. Thus, " scleroblastema " would mean the tissue differentiated from the blastema of the leg and destined to give rise to skeletal structures; myoblastema, the time differentiated for the muscles, and dermoblastema that destined for the skin.
= The figures on this and the following plates are based upon embryos belonging to the collection of Prof. Mall. I am greatly indebted to him for the use of these embryos.
Charles E. Bardeen 165
sclerotome. From here the couJciisation extends dorsally between the medial surface of the posterior half of the corresponding myotome and spinal ganglion and gives rise to a dorsal, or neural, process (Figs. 5 and 6, Plate 2, N. Pr.). Kt the same time it proceeds ventrally along the distal margin of the corresponding myotome and gives rise to a ventral or costal process (Figs. 5 and 6, C.Pr.); and medially toward the chorda dorsalis, giving rise to a process which joins about the chorda dorsalis with a similar one, from the other side of the segment (Figs. 5 and 6, Disk). These median processes by their fusion form what has been termed by Weiss, oi, a "horizontal plate." "Primitive dish" seems to me perhaps a better term.
The whole mass of condensed tissue which gives rise to the primitive dorsal, ventral and median processes has received various designations, of which that given by Froriep, 83, " primitive vertebral arch " seems to be the most widely accepted. Since, however, it represents much more than a vertebral semi-arch, I have previously, 99, suggested for it the term " scleromere." *
Figs. 8, 9 and 10, Plate III, represent wax-plate reconstructions of several scleromeres from the thoracic region of Embryo II, length 7 mm. The outlines of the condensed tissue are not so sharp in nature as it is necessary to make them in a model of this kind. It is believed, however, that the general form relations are here fairly accurately shown. In Fig. A, Plate II, of the article by Bardeen and Lewis are shown the relations of the scleromeres to other structures.
During the period of differentiation of the scleromeres the myotomes undergo a rapid development. The median surface of each myotome gradually protrudes opposite the fissure of v. Ebner. The dorsal and ventral processes of each scleromere are then slowly forced into the interval between the belly of the myotome to which it belongs and the one next posterior, and thus finally they come to occupy an intersegmental position. It is not, however, correct to call the early processes of the scleromeres myosepta" as some text-book writers have done. Fig. 4 shows this.
By the fissure of v. Ebner each sclerotome is divided into two portions, of which the posterior in the higher vertebrates plays the chief role in vertebral differentiation. " Scleromere " therefore seems an appropriate designation for the condensed sclerogenous tissue of this half-segment. Goette has recently, 97, brought forward evidence in favor of the view that primarily in the digitates there were two vertebrae to each body-segment. In the higher vertebrates, during embryonic development, the posterior skeletal area of each body-segment alone develops freely. The anterior area becomes fused with the scleromere in front.
166 Development of Thoracic Vertebra) in Man
This figure represents a horizontal section passing through several spinal ganglia, myotomes and neural processes. The last may be seen extending gradually into the area opposite the myotomic septa, but they still cover the whole posterior half of the median surface of the myotome in the region of the section. The processes are connected by membranous thickenings of the mesenchyme of the anterior half of each segment. These membranes may be called interdorsal membranes. They correspond to the interdorsalia of elasmobranchs. Jb'igs. 12, 13, 15 and 16, Idr. M., represent these membranes. A line drawn from A to B in Fig. 12 would pass through an area corresponding to that of the section represented in Fig. 4.
In the region where the neural and costal processes spring from the primitive disks membranous septa are likewise differentiated from the anterior halves of the sclerotomes. These septa serve to unite the successive disks. Each is continuous posterially with a dense tissue which strengthens the primitive disk and anteriorly it extends into the neural and costal processes. The relations of these interdiscal membranes are shown in Figs. 3, 11, 12 and 13, Ids. m. Since at this period structural outlines are by no means sharp, the figures based upon wax-plate reconstructions must be taken as semi-diagrammatic. A line drawn from c to d^ in Fig. 12 would represent essentially the plane of the section shown in Fig. 3.
During the development of the interdiscal membranes the primitive disks become hollowed out on the posterior surface. A comparison of Fig. 2 with Fig. 3 demonstrates this. The perichordal sheath meanwhile is developed in a ventrodorsal direction so that the area between the primitive disks becomes divided into right and left halves. Figs. 11, 13 and 7 all show this. Each lateral area is filled with a lightly staining mesenchyme which is continuous ventrally and dorsally with the tissue surrounding the spinal column.
Fig. 17, Plate V, represents a sagittal section cut slightly obliquely through an embryo 12 mm. long. In the region where the chorda {Ch. d.) is cut, the primitive disks may be seen united by a fairly dense tissue, the perichordal septum (Sptm.). Posterior to this region the section passes to one side of the chief axis of the embryo. The intervertebral disks may here be seen separated by a lighter tissue and in the more posterior portion of the section, which passes still more lateral to the chordal region, the tissue between the disks is seen to be continuous with that surrounding the spinal column. In this region the interdiscal membrane (Ids. m.) is seen anterior, the primitive disk posterior to the fissure of v. Ebner {F. v. E.).
Charles E. Bardeen 167
Meanwhile the ventral processes of the thoracic vertebra extend well into the thoracic wall, giving rise to primitive ribs, illustrated in Fig. B, Plate II, in the article of Bardeen and Lewis, oi.
Development proceeds rapidly. In Embryo CIX, length 11 mm., age about five weeks (Figs. 14-16), the conditions are as follows: The neural processes are somewhat better developed than those of the preceding stage, but otherwise are similar in character. The costal processes are considerably farther developed (Bardeen and Lewis, oi, Plate V, Fig. E). At the angle between the neural and costal processes opposite where they join the primitive disks a transverse process, but slightly indicated at the preceding stage, is now fairly clearly marked. Each primitive disk has become further hollowed out at its posterior surface, owing, in all probability, to the conversion of its tissue into that of the area between the disks. The interdiscal membrane (Ids. m.), on the other hand, has become thicker and has extended anteriorly and posteriorly about the area between the disks so that this has become completely enclosed (Figs. 14, 15 and 16). The tissue of each segment immediately anterior to the primitive disk has become greatly thickened and the line between it and the disk indistinct.
The area between each two primitive disks is still divided by the perichordal septum (Fig. 7). Each half represents the anlage of a chondrogenous center of the vertebral body. Formation of cartilage has not, however, begun. The thickening of the ventral margin of the primitive disk at this stage represents the "hypochordal Spange," which Froriep has shown to play an important part in the development of the vertebrae of birds and of the atlas in mammals. It has merely a transitory existence in the thoracic region of man.
Summary. — To sum up briefly, we may say that during the blastemal period each scleromere becomes divided into two portions, an anterior and a posterior, characterized by a much greater condensation of tissue in the posterior. From this condensed tissue arises a primitive vertebra of Eemak, or scleromere, with dorsal (neural) and ventral (costal) processes and a disk uniting them to the mesenchyme condensed about the chorda dorsalis. From the tissue of the anterior half of each sclerotome arise membranes which serve to unite the dorsal processes of the scleromeres, interdorsal memhranes, and to cover in the areas between the successive disks, interdiscal membranes. The primitive disks become hollowed out posteriorly by a loosening up of their tissue and strengthened anteriorly by a condensation of the tissue immediately bounding the fissure of V. Ebner. The area between each two disks is bilaterally divided by a membrane springing from the perichordal sheath. The formation of a cartilagenous skeleton now begins.
168 Dovelopniont of Thoracic A'ertebra^ in Mnn
Chondrogenous Period.
The tissue rehitions during this period have been carefully stndied in representatives of most of the chief groups of vertebrates. The form of the early structures has been less accurately determined because most investigators have avoided the somewhat laborious methods of plastic reconstruction.
On each side of the blastemal vertebra three primary centers of chondrification appear at about the same time, one for neural process, one for the costal process and one for the vertebral body. Fig. 7, Plate II, shows these centers as they appear in a cross section at an early period. Figs. 25, 26 and 27, Plate VI, show the early cartilages of an embryo slightly older, CXLIV, length 14 mm., age 5-| weeks.
The cartilages of the vertebral body develop by a transformation of the tissue lying between the primitive vertebral disks and surrounded by the interdiscal membrane. A considerable part of this tissue is derived from the posterior surface of each primitive disk. At first the cartilage of the left side is separated from that of the right by the perichordal septum. Soon this is broken through and the tAvo anlages of cartilage become united about the chorda. In the thoracic region this imion seems to take place at about the same time dorsally that it does ventrally. A sagittal section of an embryo at this stage is shown in Fig. 18. The chorda dorsalis is surrounded by a perichordal sheath. The latter is encircled by dense intervertebral disks which alternate with light cartilagenous rings. The latter are surrounded by perichondriimi which is less condensed than the tissue of the disks, but more so than that of the bodies and about the same as that of the perichordal sheath. Ventrally and dorsally a longitudinal ligament has been differentiated from the surrounding mesenchyme.
It is probable that the disks seen in this section are formed in part from the primitive disks, in part from the posterior layer of the anterior sclerotome halves ; in other words, that each is formed about the rudiment of the fissure of v. Bbner. Compare Figs. 17 and 18. The tissue is concentrically arranged in a way somewhat resembling that of the intervertebral disks of the adult.
The perichordal tissue rapidly decreases in thickness. At the same time the cartilage of the vertebral bodies grows also at the expense of the intervertebral disks (Figs. 19, 20, 21 and 22). According to Schultze, 96, the cartilages of the bodies finally fuse to form a continuous cartilagenous column. This does not seem to be the case in man. In all of the embryos belonging to the collection of Prof. Mall some membranous tissue may be seen separating completely the successive bodies,
Charles E. Bardeen 169
but in embryos between 20 and 40 mm. in length tliis membrane in tlie vicinity of the chorda dorsalis is very thin. At the periphery of the disks the annnlns fibrosns is meanwhile differentiated more and more into a condition resembling the adnlt (Figs. 17-23, Plate V).
The chorda dorsalis at the period shown in Fig. 18 is of about the same size at the level of the disks and between them, but as the bodies increase in size at the expense of the disks the chordal canal becomes enlarged in the intervertebral areas and constricted at the centers of the bodies (Figs. 19, 20 and 21). The chorda loses its continuity and the chordal cells become clumped in the vicinity of the disks (Figs. 21 and 22) and finally spread out there in the form of a flat disk (Fig. 23) . At this last period the perichondrium of the bodies is again becoming well marked and the portion of each intervertebral disk in the vicinity of the chorda dorsalis is better developed than during the stages immediately preceding. The chordal canal long remains in the vertebral body (Figs. 23 and 24).
The cartilage of the bodies in Embryo CXLIV(Fig. 18) is of an early embryonic hyaline type. At a slightly later stage (Fig. 19) two regions may be distinguished, a central and a peripheral. The central cartilage is denser than that of the preceding stage, while the peripheral cartilage resembles it. Gradually the cartilage at the center of the body undergoes further changes. The cells enlarge and become sharply set off against the intercellular substance (Figs. 22, 23 and 24), and finally an invasion of blood vessels takes place, chiefly from the posterior surface (Fig. 23). These changes in the cartilage, represented also in Fig. 41, Plate VII, are preliminary to ossification.
Deposit of calcium salts and actual ossification begins in the distal thoracic and proximal lumbar vertebrse of embryos about 5 to 7 cm. long and three months of age. Fig. 42 shows a center of ossification in an embryo of 70 mm.
During the development of the vertebral bodies changes have been active in the neural cartilages. At the period represented in Fig. 7, Plate II, the neural cartilage is a small, flat body situated in the dorsal process of the scleromere; from this as a center, pedicular, transverse, anterior (superior) and posterior (inferior) articular, and laminar processes are rapidly developed. This structural differentiation is best followed in the figures representing the models (Figs. 25-36). The pedicular processes are at first slender rods (Fig. 26), each of which grows out towards and finally fuses with its corresponding vertebral body. Froriep has shown (83) that in the chick this process forms a more essential element of the body than in mammals. In the atlas it forms a lateral half of the
170 Development of Tlioracic VertebrsE in Man
ventral arch, but in the thoracic region of mammals it fuses with the antero-lateral portion of the corresponding vertebral body. After its junction Avith this the pedicle increases in size but otherwise shows no marked alteration of form.
The transverse process is at first a short projection which lies at some distance from its corresponding rib (Fig. 26), The cartilagenous rib rapidly increases in size and at the same time the transverse process grows outward and forward to meet it (Figs. 29, 32 and 34), At first the developing cartilage of the rib and that of the transverse process are embedded in a continuous blastema, but before chondrification has proceeded far, branches from successive intervertebral arteries become anastomosed in the area between the neck of the rib and the transverse process and separation is effected (Figs. 36, 38 B and 39).
Between the extremity of the transverse process and the rib a joint is developed (Figs. 39, 40, 41 and 42), and the surrounding blastema converted into costo-transverse ligaments.
The articular processes develop slowly from the cartilage. Extension takes place anteriorly, A. A. Pr., and posteriorly, F. A. Pr., in the interdorsal membrane. In an embryo of 14 mm. (Figs. 25, 26 and 27) these articular plates are separated by a distinct interval. In one of 17 mm. they have approached each other very closely (Fig. 37) ; and in one of 20 mm. not only do the articular processes show distinctly more form (Figs. 28, 29 and 30), but in addition the superior articular process slightly overlaps the inferior (Fig. 38). This overlap of the superior articular processes is distinctly more advanced in an embryo of 28 mm. (Fig, 39), and still more so in one of 33 mm. (Figs, 31-33), In an embryo of 50 mm, (Figs. 34, 35 and 40) conditions essentiall} like the adult have been reached.
The laminar processes scarcely exist in Embryo CXLIV (Fig. 26). In Embryo XXII (Fig. 29) they have begun to project posteriorly to the region of the articular processes (Fig. 29). The dense embryonic connective tissue covering the laminar processes at this stage gives attachment to a membrane covering, the dorsal musculature, F. D. M., and to a membrane surrounding the spinal cord, M. R. D. This accounts for the two projections seen dorsally on the side of the model representing the membranous tissue. In Embrj^o CXLV, length 33 mm., the laminar processes extend well toward the dorsal line (Figs. 32 and 33) ; in Embryo LXXXIV, length 50 mm. (Figs. 34, 35 and 40), they completely encircle the spinal canal and from the region of fusion of each pair a spinous process extends distally, though not so far as in the adult.
Alterations in the cartilage of the neural processes preliminary to
Cliarles R. Bardeen 171
ossification begin at about the time they take place in the vertebral bodies. They are first seen in an area which corresponds to that in which the nenral cartilage begins. The earliest calcification appears in Embryo CLXXXIY, length 50 mm., in the arches of the first cervical to the sixth thoracic vertebrae.
The development of the ribs I shall not attempt in this place to describe in detail. Figs. 35-34 and 37-42 show sufficiently well the relations of the proximal ends of the ribs to the vertebrae. They are developed opposite the intervertebral disks. The blastemal tissue which surrounds the developing heads of the ribs becomes converted into costo-vertebral ligaments. Differentiation in the cartilage preliminary to ossification takes place in the shafts of the ribs even earlier than in the vertebral bodies and in the neural processes. Ossification is well under way in the shafts of the ribs of Embryo LXXIX, length 33 mm. ; XCVI, length 44 mm. ; XCV, length, 46 mm. ; and LXXXIV, length 50 mm.
Summary of the Chondrogenous Period of Vertebral Development. — Each cartilagenous vertebra is developed from four centers of chondrification. In addition, a separate center appears for each rib. In comparing these centers with the blastemal formative centers, we find that each primative center of blastemal condensation enters into union with tissue derived from the anterior half of the body-segment next posterior and then gives rise to three centers of chondrification, one for the neural arch, one for the rib and one for half a vertebra. When ossification first takes place the centers for the ossification of the neural arches and the ribs correspond to the original chondrification centers in the blastema, but the centers for ossification of the bodies show little trace of the bilateral condition which marks the cartilagenous fundaments.
The processes of chondrogenous form differentiation are shown in the drawings of the models. The period of ossification of the vertebras has been so often and so well described that no attempt will be made to enter upon a further ncount oE it in this paper. I have, however, not found two primary ossification centers, such as Eenault and Eambaud have described, for each neural arch.
LITERATURE.
Bade, P. — Die Entwicklung des menschl. Skelets bis zum Gebiirt. Arcliiv
mikr. Anat., LV, 245-290, 1900. Baldus. — Die Intervertebral Spalte v. Ebners und die Querteilung der
Schwanzwirbel bei Hemidactylus mabuia. Dissertation, Leipzig, 1901. Bardeen. — Development of the Musculature in the Body-wall of the Pig.
Johns Hopkins Hospital Reports, IX, 367, 1S99. 12
172 Development of Thoracic Vertebra! in ]\Ian
and Lewis. — Development of the Back, Body-wall and Limbs in Man.
American Journal of Anatomy, I, 1, 1901. V. Bbner. — Urwirbel und Neugliederung der Wirbelsaiile. Wiener Sitzungsberichte, XCVH, 3 Abtheil, 1S88.
Ueber die Beziehungen des Wirbels zu den Urwirbeln. Wiener Sit zungsberichte,, CL Abth. 3, 1892. Froriep. — Zur Entwicklungsgesch. der Wirbelsaiile. Arcbiv f. Anatomie und
Physiologie, Anat. Abth., 177-184; 1883, 69-150, 1886. Gaupp. — Die Entwicklung der Wirbelsaiile. Zool. Centralblatt, IV, 533-546,
S49-S53, 889-901, 1897. GoETTE. — Ueber den Wirbelbau bei den Reptilien und einigen andern Wir belthieren. Zeitschrift. f. wiss. Zoologie, LXH, 343, 1897. Hagen. — Die Bildung des Knorpelskelets beim menschl. Embryo. Archiv f.
Anatomie und Physiologie, Anat. Abth., 1900. Hasse. — Die Entwicklung des Atlas und Epistropheus des Menschen und der
Saugethiere. Anat. Studien, I, 1873. Hay. — On the Structure and Development of the Vertebral Column of Amfa.
Field Columbian Museum Publications, Zool. Series V, 11, 1897.
American Naturalist, XXXL 397-406, 1897. HoLL, M. — Ueber die richtige Deutung der Querfortsatze der Lendenwirbel,
etc. Wiener Sitzungsb., 3 Abth., LXXXV, 181-232, 1882. Kapelkin. — Zur Frage iiber die Entwicklung des axialen Skelets der Amphi bien. Bull. Soc. Imper. d. Naturalisten, Moscow, 1900, 433-440. KoLLMAXX. — Die Rumpfsegmente menschlicher Embryonen von 13-35 Urwirbeln. Archiv f. Anatomie und Physiologie, Anat. Abth., 1891. Macalister. — The Development and Varieties of the 2d Cervical Vertebra. Maxner.— Zeitschrift f. wiss. Zoologie, LXVL 43, 1899. Mannich. — Beitrage zur Entwicklung der Wirbelsaiile von Endypleschry scome. Jenaische Zeitschr., XXXVH, 1-40, 1902. Moser, E. — Ueber das Wachsthum der menschlichen Wirbelsaiile. Dissertation, Strassburg, 1889. Rambaud et Renault. — Origlne et developpement des os. Paris, 1864. RiDEwooD. — On the Development of the Vertebral Column in Pipa and
Xenopus. Anat. Anzeiger, XIH, 1901. SchatjINsland. — Uebersicht iiber die Entwicklung der Wirbelsaule in der
Reihe der Vertebraten. Verhandl. Deutsch. Zool. Gesellsch., Wiirz burg, 112-113, 1903. ScHOMBURG, H. — Entwicklung des Muskeln und Knochen des menschlichen
Fusses. Dissertation, Gottingen, 1900. ScHULTZE. — Ueber embryonale und bleibende Segmentirung. Verhandl. der
Anat. Gesellschaft, 10 Vers., Berlin, 87-92, 1896. Weiss, A. — Die Entwicklung der Wirbelsaiile der weissen Ratte, besonders
der vordersten Halswirbel. Zeitschr. f. wiss. Zoologie, LXVL 492,
1901.
Welcker. — Ueber Bau und Entwicklung der Wirbelsaiile. Zoolog. Anzeiger, 1878.
Charles IJ. Bardeen 173
ABBREVIATIONS USED TO DESIGNATE STRUCTURES ILLUSTRATED
IN THE FIGURES.
A. A. Pr., anterior articular process. N. Pr., neural process.
C. v., cardinal vein. Pch. 8., perichordal sheath.
C Pr., costal process. P. A. Pr., posterior articular process.
Cocl., coelom. Pd., pedicle.
Ch. d., Chora dorsalis. Rih, rib.
Der., dermis. Scl., sclerotome.
Disk., intervertebral disk. Sptm., perichordal septum.
D. L., dorsal ligament. 8p. C, spinal cord.
D. M., dorsal musculature. Sp. O., spinal ganglion.
F. V. E., fissure of v. Ebner. Sp. N., spinal nerve.
F. D. M., fascia of dorsal musculature. Sp. Pr., spinous process.
Ids. M., interdiscal membrane. Trap., trapezius.
Idr. M., interdorsal membrane. Tr. Pr., transverse process.
Is. A., intersegmental artery. V. L., ventral ligament.
L., lamina. Y. B., vertebral body.
Myo., myotome. .5, 6, 7, 5th, 6th and 7th thoracic vertebrae.
M. R. D., membrana reuniens dorsalis.
EXPLANATION OF FIGURES. PLATE I. Figs. 1, 2, 3 and 4. Frontal sections through the thoracic region of several embryos during the blastema! period of vertebral development. 47.5 diam. (1) Embryo CLXXXVI, length 3.5 mm. (2) Embryo LXXX, length 5 mm. (3) and (4) Embryo CCXLI, length 6 mm. (3) Through the region of the chorda dorsalis, (4) through a more dorsal plane. Figures 1, 3 and 4 represent sections cut somewhat obliquely so that the right side of the sections is ventral to the left. In Figs. 2 and 4 on the right side the bodies of several embryonic vertebrse are represented in outline. In Figs. 2 and 3 owing to artefacts the myotomes are pulled away from the sclerotomes.
PLATE II. Figs. 5, 6 and 7. Cross-sections through midthoracic segments during the blastemal period of vertebral development. 55 diam. (5) Embryo LXXVI, length 4.5 mm. The right side of the section passes through the middle, the left side through the posterior third of the 5th segment. (6) Embryo II, length 7 mm. 5th thoracic segment. The right side of the drawing represents a section anterior to that shown at the left. (7) Embryo CLXXV, length 13 mm. The left half of the 6th vertebral body, neural process and rib are drawn in detail, the body-wall, spinal cord and spinal ganglion are shown in outline.
PLATES III AND IV. Figs. 8, 9, 10, 11, 12 and 13. Views of models representing the blastemal stage of vertebral development. (8-10) Embryo II, length 7 mm., 33% diam. (11-13) Embryo CLXIII, length 9 mm., 25 diam. (14-16) Embryo CIX, length 11 mm., 25 diam. 8, 11 and 14 views from in front; 9, 12, 15, views from the side; 10, 13, 16, views from behind.
174: DGVclo]-)incnt of '^^Phoi-acio Ycrtebrns in ]\ran
PLATE V.
Figs. 17-24. Sagittal sections in the mid-line through the 6th, 7th and 8th thoracic segments of a series of embryos from 12 to 50 mm. long. (17) Embryo CCXXI, length 12 mm. This section includes several segments anterior and posterior to the three above mentioned, 6th, 7th and 8th. (18) Embryo CXLIV, length 14 mm. (19) Embryo CVIII, length 22 mm. (20) Embryo LXXXVI, length 30 mm. (21) Embryo CXLV, length 33 mm. (22) Embryo LXXIX, length 33 mm. (23) Embryo XCVI, length 44 mm. (24) Embryo CLXXXIV, length 50 mm.
PLATE VI.
Figs. 25-35. Dorsal, lateral and ventral view^s of models made by the Born method to illustrate vertebral form-differentiation in the 6th, 7th and 8th thoracic vertebrae during the chondrogenous period. On the left side the cartilagenous, on the right the enveloping fibrous tissue is shown. The latter is also shown on the eighth vertebra in Figures 29 and 35. (25-27) Embryo CXLIV, length 14 mm., 20 diam. (28-30) Embryo XXII, length 20 mm., 13 diam. (31-33) Embryo CXLV, length 33 mm., 10 diam. (34, 35) Embryo LXXXIV, length 50 mm., 10 diam. (34) Dorsal view, left half; (35) median view.
PLATE VII.
Figs. 36-42. Transverse sections through mid-thoracic vertebrae of a series of embryos. 5 diam. (36) Embryo CVI, length 17 mm. (37) Embryo CCXVI, length 17 mm. (38) Embryo XXII, length 20 mm. (39) Embryo XLV, length 20 mm. (40) Embryo LXXXIV, length 50 mm. (41) Embryo XLIV, length 70 mm. (42) Embryo XXIII, length 70 mm.
Tlie models from ivliich the illustrations in this article were drawn have been reproduced hy Dr. B. E. Dahlgren at the American Museum of Natural History, New York, N. Y., and arrangements may he made for securing copies hy applying to the Director of the Museum.
THE DEVELOPMENT OF THE THORACIC VERTEBR/E IN MAN
C. R. BARDEEN
PLATE I
Fi3.2
Fig.f
AMERICAN JOURNAL OF ANATOMY—VOL. I>
THE DEVELOPMENT OF THE THORACIC VERTEBR/C IN MAN
C. R. BARDtEN
PLATE II
AMERICAN JOURNAL OF ANATOMY—VOL. IV
THE DEVELOPMENT OF THE THORACIC VERTEBRy€; IN MAN
C. R. BARDEEN
PLATE III
Pch.S.
Disk
N.Pr.
Fig. 1 2
Disk,
Xhd
ls.A
Fis.lO
Ch.d.
Fis. 13
AMERICAN JOURNAL OF AN ATOM Y- -VOL. IV
THE DEVELOPMENT OF THE THORACIC VERTEBR/E IN MAN
C. R. BARDEEN
PLATE IV
Sptm.
CPr.
CPr.
Rg.lt
AMERICAN JOURNAL OF ANATOMY— VOL. IV
THE DEVELOPMENT OF THE THORACIC VERTEBR/E IN MAN
C. R.- BARDEEN
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C. R. BARDEEN
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AMERICAN JOURNAL OF AN ATOM Y- -VOL. IV
THE DEVELOPMENT OF THE THORACIC VERTEBR/E IN MAN
C. R. BARDEEN
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AMERICAN JOURNAL OF ANATOMY— VOL. IV 13
THE ELASTIC TISSUE OF THE HUMAN LARYNX.
BY
DEAN D. LEWIS, M. D.
From the Hull Laboratory of Anatomy, University of Chicago.
With 5 Plates.
The elastic tissue of the hirviix. since it was first described b}' Lauth/ in 1835, has been the object of frequent studies by anatomists and laryngologists. The functional importance of this tissue in the production and modification of voice has aroused interest in its distribution and arrangement, and while the earlier descriptions, which are based upon the study of specimens prepared by methods which do not reveal the finer elastic fibrils, are correct, a knoAvledge of the more minute relations existing between the elastic fibers, muscle, cartilage and epithelium is desirable.
The introduction of specific stains for elastic tissue has given a new impetus to its study from a developmental and pathological view-point, and has drawn attention to the elastic tissue of the larynx, as is evidenced by the number of articles appearing upon the subject. Friedrich's work followed closely upon the introduction of the Taenzer-Unna orcein stain, and Katzenstein, using the Weigert resorcin-fuchsin method, has repeated recently the former's work. The Weigert method certainly differentiates the elastic fibers more distinctly than the Taenzer-Unna method, and stains the finer fibrils, which may escape the latter. These two investigators agree in general, but differ in so many points that the publication of this article, which was about completed when Katzenstein's article appeared, seems justified.
The specimens from which this study is made were prepared from the larynges of the new-born. They were hardened in alcohol and Zenker's fluid. The former fixative, recommended by Weigert, gives excellent results, but equally good results are obtained after fixation in Zenker's fluid. The ordinary celloidin technique was used, with the addition of
'Lauth: Mem. de I'acad. royale de med., 1S35, t. 4, p. 98. American .Joukxal of Anatomy. — Vol. IV.
176 The Elastic Tissue of the Iluinan Larynx
the slow method of celloidin infiltration, as recently recommended by Miller.' ■
Sections, fifteen micra in thickness, were made and mounted serially. The sections were passed through a mixture of alcohol and glycerine, from which they were transferred to a paper corresponding in size to the cover-glass to be used. The paper Avas then inverted upon a slide, which had previously been coated with a thin layer of albumin fixative. Between two slides thus prepared a piece of filter paper was inserted, and the two slides were tied together. They were then placed in a thermostat until dry, when they were removed and placed in equal parts of absolute alcohol and ether to remove the celloidin. The sections are always firmly attached, and no care need be exercised to prevent their floating oif. This method Avas devised by Prof. E. C. Jeffrey. Weigert's resorcin-fuchsin method was used to stain the elastic fibers. Orange G. as a counterstain offers a sharp contrast to the blue-black of these fibers. Van Gieson's picro-fuchsin was used in studying the collagenic fibers and the nodules found in the anterior extremities of the vocal cords.
Henle ' describes beneath the mucous membrane of the larynx an elastic fiber layer, which in some regions is poorly, and in others well developed, and in some closely and in others loosely connected with the epithelium. Where this layer is thickened after removal of the mucous membrane or the tissue which covers them externally, there remain ligaments. These ligaments are attached at definite points to the perichondrium of the laryngeal cartilages, and such points of attachment may be regarded as the points of origin of the ligaments. It is not to be disregarded, however, that the elastic fibers of these ligaments are in direct continuity with the elastic elements of the whole mucous tract, and that, therefore, their limits are not sharp and are arbitrarily made.
Following the classical description of Luschka * the elastic tissue of the larynx may be divided for descriptive purposes into three zones, corresponding to the three compartments of this organ. The inferior zone includes all the elastic tissue within and below the ligamenta vocalia ; the middle zone includes the elastic tissue surrounding the ventriculus laryngis; the superior zone includes the elastic tissue of the membrana quadrangularis and epiglottis. The discussion of the arrangement of the elastic fibers will be proceeded with in the order given above.
= Miller: J. of Applied Microscopy and Laboratory Methods. Rochester, N. Y., Vol. 6, No. 4.
^ Henle: Handb. der Eingeweidelehre des Menschen. Braunschweig, 1873, p. 254.
■•Luschka: Der Kehlkopf des Menschen. Tiibingen, 1874.
Dean D. Lewis 17T
ELASTIC TISSUE OF INFERIOR ZONE.
Coxus Elasticus (Luschka) : Liog. Crico-thyreo-aryt^exoidea OF Krause ' AXD Leg. Cricotiiyreoideum Medium (Hexle).
If a lamina of the thyroid cartilage and the subjacent muscle be removed, a fan-shaped mass of elastic fibers will be seen, which passes from the angle of the thyroid cartilage downward, backward and laterad to be attached to the ascending upper border of the cricoid cartilage and the inferior surface of the vocal process of the arytenoid cartilage. This elastic membrane is the conus elasticus of Luschka. Sections at various levels through it will be described.
In frontal sections, made through the anterior part of the conus elasticus, a dense network of elastic fibers arising from the upper border of the cricoid cartilage, and passing cephalad and laterad to be attached to the lower border of the thyroid cartilage, will be seen. The fibers composing this network tend to pass vertically, anastomose freel}, and some of the fibers arise on each side of an indefinite median raphe. On both sides these fibers are continuous with elastic fibers passing from the upper border of the cricoid cartilage. The mass of elastic fibers occupying the median line form the ligamentimi cricotiiyreoideum medium, and are seen to be merely the anterior continuation of the conus elasticus, as previously shown by His. This ligament is pierecd by the cricothyroid artery, and the arrangement of some of its component fibers about a median raphe suggests that functionally it is divided into symmetrical parts. (See Fig. 1.)
In frontal sections made through the middle of the conus elasticus, elastic fibers, few in number, and small in size, are seen arising from the upper border of the cricoid cartilage, and passing cephalad and mediad to reach the ligamentum vocale. These fibers, increasing constantly in number and size as they ascend, form a gentle curve, the convexity of which is directed mediad, being separated in the subglottic region from the subepithelial elastic layer, by numerous glands, and loose connective tissue, which favors the development of oedema at this point. The concavity is occupied by the musculus vocalis. The fibers below are obliquely arranged, and only as the plica vocalis is approached do they tend to become sagittally directed and parallel. (See Fig. 2.)
Sections made through the posterior part show that the conus l)ecomes shorter and approaches nearer the median line. The fibers are more nearly vertical in arrangement, passing up to the inferior surface of the
'Krause: Handb. der menschlichen Anatomie. Hannover, 1879.
178 The Elastic Tissue of the Human Larynx
vocal process of the arytenoid cartilage. While these sections are instructive, much more may he learned 1)y tracing transverse sections serially.
In transverse sections made through the ligamentum crieothyreoideum medium, the elastic fihers are found grouped in well-defined vertical bundles, which are separated from each other by horizontal fibers passing inward toward the indefinite median raphe. Fine elastic fibers, vertically directed, which surround numerous groups of mucous glands, pass from the subepithelial layer to the ligament. (See Fig. 4.)
More posteriorly the fibers of the conus pass obliquely, upward, forward and mediad, but they are intersected by other fibers passing almost at right angles to them. The oblique fibers predominate, both in size and number. Traced backward, the elastic fibers of the conus are found to be attached to the cricoid cartilage. Anastomosing fibers, most numerous anteriorly, connect the fibers of the conus with the subepithelial layer, where the two systems are not separated by the glands previously mentioned. (See Fig. 5.)
In transverse sections just below the ligamentum vocale, the arrangement of elastic fibers anteriorly has been accurately described by Friedrich. The elastic tissue, reduced in amount, is replaced by collagenic fibers, which separate the fibers of the conus from the hyaline substance of the thvroid cartilage. This collagenic tissue is rich in glands. The nearer the ventricle is approached, the more nearly horizontal the fibers become to form the
Ligamentum Yocale. {See Fig. 7.)
Henle,* in describing the ligamentum vocale, states that some of its elastic fibers fuse posteriorly with the elastic cartilage, forming the vocal process of the arytenoid. Other fibers are attached about the spina inferior, above the vocal process, and from this attachment fibers course upward posterior to the ventricle of the larynx. Still other fibers are inserted below the vocal jDrocess upon the medial surface of the arytenoid cartilage, or upon the anterior surface of the cricoid cartilage.
Kanthack ' describes posteriorly a sesamoid cartilage, which marks the point of transition of the elastic fibers of the ligamentum vocale into the vocal process of the arytenoid cartilage.
Reinke's * description of the arrangement of the elastic fibers at the posterior extremity of the ligamentum vocale, and their relation to the
Henle: Handb. der Eingeweidelehre des Menschen; p. 255. 'Kanthack: Arch. f. path. Anat., etc.. Berl.. Bd. cxvii, p. 533. ^Reinke: Anat. Hefte. Bd. ix, pp. 108-110.
Dean D. Lewis . 179
processus vocalis of the arytenoid cartilage, is the most accurate that has yet been given. His findings can merely be verified; nothing can be added. He states tliat in macroscopical preparations it can be seen that the ligamentum vocale has a wide area of attachment to the vocal process of the cartilage, covering its upper and medial surfaces, leaving the lower and lateral surfaces free for the attachment of the fibers of the musculus vocalis. The study of microscopical preparations made in frontal and horizontal planes shows that the middle fibers of the ligament, only, are the direct continuation of the fibers of the elastic cartilage, which forms the apex and anterior border of the vocal process. The greater number of fibers, occupying the lateral part of the ligament, are derived from the perichondrium, which consists here almost wholly of elastic fibers, which cover the elastic cartilage above, laterally and medially.
In the beginning of the elastic cartilage the fibers intersect each other at various angles, but soon pass parallel in a sagittal plane. The fibers of the perichondrium upon the medial and lateral surface of the cartilage pass in front of the apex and anterior border of the processus vocalis in curves, which intersect each other at right angles. All these fibers form anterior to the vocal process a dense network, probably the sesamoid cartilage of Kanthack, out of which parallel fibers emerge, to pass forward. The fibers of the ligament receive from the side additional fibers, which lie between the bundles of the musculus vocalis, and by means of its perimysium they are attached to the vocal process of the arytenoid cartilage.
In the middle part of the ligament the fibers usually course parallel to each other, and in a sagittal direction. When the processus vocalis is in the position of rest, two great divisions of the ligament may be differentiated. The one adjacent to the muscle is dense and only in thin sections can the separate fibers be differentiated; the other, equally wide, borders upon the preceding, above and medially, and has the same form. In sections, it is recognizable as a lighter zone. The fibers of the denser part of the ligament form a curve, the concavity of which is directed toward the free border of the labium vocale, while the fibers of the less compact part are straight.
Upon superficial examination, the fibers of the ligament seem to pass parallel to each other, without anastomosing. C. L. Merkel has stated that the elastic fibers of the ligamentum vocale differ from the elastic fibers in other parts of the body, in that they do not anastomose. Reinke has shown, however, by the use of specific stains and higher lenses that there are anastomosing fibers, but that. the principal fibers are so well
180 The Elastic Tissue of the Human Larynx
developed that it is difficult to see the finer anastomosing ones. Eeinke's description is most accurate, and he has demonstrated that the elastic fibers of the ligament have a definite structure, relative to their function. His conclusions may be summed up as follows: The elastic fibers of the ligamentum vocale attain their greatest development in planes parallel to constant tension, and at right angles to constant pressure, while the fibers passing obliquely to anastomose with either of the above systems remain atrophic or have disappeared.
The Anterior Attachments of the Ligamenta Vocalia.
There is so mucii difference of opinion among anatomists and laryngologists concerning the anterior attachment of the ligamentum vocale, that some account of the views held by the different investigators may be expedient.
C. Mayer ° was the first to describe in the anterior extremity of each ligament a small cartilaginous nodule, which was found by him in man, and some of the higher apes. These nodules are sometimes designated as the " cartilagines sesamoide^ anteriores." (See Fig. 8.)
Gerhardt " noted in sections made at the level of the insertion of the ligamenta vocalia into the thyroid cartilage a small firm median process, occupying the angle of the thyroid cartilage, which he considered to be formed from its hyaline substance. This median process is prolonged on each side by yellowish flexible bands into the anterior extremities of the ligamenta vocalia. The yellowish color of the anterior commissure and its thickening is produced by these processes. The intimacy of the relation between the median process and its lateral prolongations is variable. However, Gerhardt macerated sections many days in water, but was still unable to separate them without the use of a knife. He considered that microscopically there is repeated at the anterior commissure the same histological structure that Rhciner had previously described for the processus vocalis of the arytenoid cartilage, and suggested that this median process, with its lateral prolongations, be known as the processus vocalis of the thyroid cartilage.
Yerson " notes that the ligamentum vocale is thickened to form a small nodule immediately behind its attachment to the angle of the thyroid cartilage. Upon sectioning this nodule, it is seen to l)e composed
» Mayer, C: J. F. Meckel's Arch. f. Anat. u. Physiol.; 1826, p. 194. "Gerhardt: Arch. f. path. Anat., etc., Berl., Bd. xix, pp. 436-437. "Verson: Strieker's Handb. der Lehre von den Geweben des Menschen u. der Thiere. Leipzig, 1871, p. 460.
Dean D. Lewis . ISl
of elastic fibers, roinid and spindle cells. It is found in the new-born. Chondrification never occurs in it.
Sappc}' ^' states that tlie ligauR'ntum Nocalc is atiached anteriorly by means of a nodule composed of elastic tissue, " nodule glottique anterieur.^^
Frankel " describes in the anterior extremity of the ligamentum vocale a small firm nodule, which is attached to the hyaline thyroid cartilage by loose fibrous tissue. He states that the nodule undoubtedly contains cartilage cells.
Xicolas " speaks of the " cartilagines sesamoidea^ anteviores as small white or yellowish-white nodules, which can be isolated without difficulty from the fibro-elastic tissue in which they are lodged. They do not exceed a millet seed in size; often they are smaller. They are attached to the angle of the thyroid cartilage by a dense fibrous tissue. In the majority of cases, if not in all, among the elastic and collagenic fibers forming the nodules, cells are found which are undoubtedly cartilaginous in character.
Keinke'^ describes the nodule as being composed of a deeply stainable substance, resembling histologically the tissue just anterior to the processus vocalis of the arytenoid cartilage. Some cartilage cells are found in the nodule. The elastic fibers passing off from the anterior extremity of this nodule are attached to the perichondrium of the thyroid cartilage.
jSTone of the investigators had paid much attention to the finer histological structure of the median process described by Gerhardt, and it remained for Friedrich^" to study it in detail, and to question the conclusions of the former. Friedrich describes accurately the relation existing between the collagenic fibers, occupying the angle of the thyroid cartilage, and the anterior fibers of the conns elasticus. This fibrous tissue increases in amount as sections passing cephalad are examined; it attains its greatest development opposite the anterior attachments of the ligamenta vocalia. The fibrous tissue will be found grouped in well-defined vertical bundles immediately adjacent to the thyroid cartilage. These vertical bundles are surrounded by horizontal fibers. Posteriorly, as the anterior extremities of the ligamenta vocalia are approached, the bands of fibrous tissue become horizontal, corresponding in direction to a horizontal group of elastic fibers, passing off
'-Sappey; quoted by Friedrich.
"Frankel: Arch. f. Laryngol. u. Rhinol. Bd. i.
"Nicolas: Poirier et Charpy's Traite d'anatomie huraaine., t. iv, p. 435.
Reinke: Anat. Hefte. Bd. ix, p. 110.
'"Friedrich: Arch. f. Laryngol. u. Rhinol. Bd. iv, pp. 192-193.
182 The Elastic Tissue of the Human Larynx
from the anterior extremities of the nodules described by Mayer. Interspersed throughout this fibrous tissue are some cartilage cells and fine elastic fibrils, which are verticalh' directed. (See Fig. 8.)
Friedrich states that the perichondrium passes between the hyaline substance of the thyroid cartilage and the median process described by Gerhardt, and that it forms a distinct line of separation between the two. He concludes, therefore, that there is no gradual transition from a hyaline to an elastic cartilage, as is the case in the arytenoid cartilage, and that Gerhardt is not justified in speaking of the process described by him, as the processus A-ocalis of the thyroid cartilage. Friedrich found no cartilage cells in the nodules occupying the anterior extremities of the ligamenta vocalia.
Katz(in stein," while agreeing with Friedrich in many points, takes issue with him concerning the anatomical significance of the median process. He states that the perichondrium is reflected upon the sides cf the process, and that it does not form a line of separation between the fibrous median process and the hyaline substance of the thyroid cartilage. In establishing the perichondrial relation, he makes use of the law first suggested by Eawitz, that the perichondrium exerts a directive influence upon the orientation of cartilage cells. Upon the external surface of the thyroid cartilage the cells are arranged parallel to the fibers of the perichondrium. In the center of the cartilage they lie at right angles to its long axis; upon the inner surface of the cartilage the cells are arranged parallel to the fibers of the perichondrium, until the median process is reached, where they are gathered into irregular clusters and some of the cartilage cells are displaced posteriorly. Katzenstein agrees with Gerhardt regarding the anatomical significance of this process, and considers it as quite comparable to the processus vocalis of the arytenoid cartilage. Like Eeinke, in his work upon the ligamentum vocale, Katzenstein has shown that the fibers are arranged in definite tension planes.
In some of the lower animals, white rat, cat, etc., Katzenstein has described between the laminae of the thyroid cartilage a wedge-shaped cartilage, which is covered by elastic fibers anteriorl}-, and receives posteriorly the attachment of the anterior extremities of the ligamenta vocalia. According to him, this wedge-shaped cartilage is the homologue of the median process described by Gerhardt.
While Katzenstein has accurately described the histological findings, he has misinterpreted their anatomical significance. If the developmental history of the thyroid cartilage be reviewed, some facts will be
^•Katzenstein: Arch. f. Laryngol. u. Rhinol. Bd. xiii, pp. 336-337.
Dean D. Lewis . 183
met with wliich will explain the different orientation of cartilage cells adjacent to the process, and the significance of the wedge-shaped cartilage described by the investigator.
Eambaud and Eenault/' in discussing the development of the thyroid cartilage, say that the laminae of the thyroid cartilage are united by means of a circumscribed median cartilage — " le cartilage vocal." It may be distinguished by its transparency. This cartilage is well-marked in young subjects. In the adult, however, the cartilage may not be present, but is represented by an indistinct point of ossification. It is lozenge-shaped, and its borders unite with the lamina of the thyroid cartilage.
Henle " states that horizontal sections through the thyroid cartilage show that its laminas are separated more or less distinctly from a middle piece by a condensed layer of interstitial substance, curved so that the convexity is directed mediad. This middle piece of the thyroid cartilage is the lamina mediana cartilaginis thyreoideffi of Halbertsma. In this piece the cartilage nests are smaller and more closely grouped than in the laminae. The ligamenta thvreo-arytasnoidea inferioria and their corresponding muscles arise from this part, or a connective tissue mass, connected with it. The fibers from the mass pass a short way into the middle piece, so that this tissue immediately posterior to the hyaline cartilage resembles in structure fibro-cartilage.
Nicolas '"' states that immediately after birth there is found in the median line of the thyroid cartilage, at the level of the vocal cords, a special arrangement of the cartilage cells, corresponding to the position of the lamina mediana. In the adult this middle portion of the thyroid cartilage can be distinguished from its laminae only by the different orientation of its cells.
The embryology of the thyroid cartilage explains the different orientation of the cartilage cells adjacent to the median process, and in it. I have sectioned the larynges of young dogs, and have found, occupying the space between the laminae of the thyroid cartilage, the wedgeshaped cartilage which Katzenstein states is comparable to the median process described by Gerhardt in man. I consider it to be the lamina mediana which fuses later in the lower animals than in man.
Friedrich's description of the median process is correct, with the exception of that of the perichondria! relation. The perichondrium does not i)ass between the hyaline substance of the thyroid cartilage and the
"Rambaud et Renault: Origin et devellopement des os. Paris, 1864.
"Henle: Handb. der Eingeweidelehre des Menschen; p. 243.
""Nicolas: Poirier et Charpy's Traite d'Anatomie humaine. T. 4, p. 447.
ISh 'V\\o I'lhislic 'I'issuc of the lliiiii.iii Lur^lix
libroiis tist^iio I'oni posing" tlio procc'ss. iioi- is il rcnccicd u|ion tlio sides of it. iis (Icscrihcd hy KiilziMislciii. Tlic wlmlc jtroccss is loi'iiicd by a tliickciiiiiu' of i\]o |)(M'icli(Mi(lriuin. wliicli pusses direcily l)ack\var(l to receive the iittiieliineiit o\' fli(> clastic l\\)vvs of the ligameiita vocalia. ^J'liis is indicated by the urrangeincnt o\' the chistic libers of the i)erichondriuin at this point, Avhicli, adjacent to the tliyroid cartilage, are directed eitlier antcri)-posteriorly or obliquely. Tlie attachment of the elastic fibers of the liganienta vocalia at this jioint is comparable to their attachment by means of tlie pcrii-hondriuni to the laryngeal cartilage at other points. The great increase in tlu> amount of elastic tissue in the ligamenta vocalia cieinands an increase in the number and size of the perichondrial fibers to which tlu>y are attached. This increase, gradual from below upwards, correspoiuls to the increase in the number of the tibers composing the conns elasticus, as it passes upward.
Adjacent to tlie tliyroid cartilage, the (ihers iwc grouped in vertical bundles, whit'h are separated from each other by hoi'izonfal fibers. Posteriorly, the perichondrial fibers are collected into horizontal bundles, which are separated from eacli otluu' by blood vessels, and ducts of glands, verticallv directed. Into tliese pai'alh^l bamls of librous tissue are attached })arallel bundles of elastic fibers, whicli pass oil' fi'om the nodules occujiying the anterior extremities of tlie ligamenta vocalia. Scattered throughout the jieivichondrium at this point are lin(^ elastic libers, vertically directed. I have been unable to find cartilage cells as far posterior as described by Friedrich and Katzenstein. These cells seem to be ri>stricted to a narrow zone immediately adjacent to the thyroid cartilage.
In specimens stained by Van Gieson's method, fibrous hands are seen to pass off posteriorly from perichondrium to surround a luulule, which occupies the anterior extremity of each ligamentum vocale, and which i< composed of round and spindle cells. While histologically these nodules resemble somewhat those found anterior to the processus vocales of the arytenoid cartilages, I have been unable to (iiid cartilage cells in them. (Sec Fig. 9.)
In specimens stained by Weigert's method, ilu^ elastic fibers of the ligamentum vocal(> will he sihmi to ])ass into the nodule, parallel to each other, posteriorly, wliile from its anterior extremity and medial surface^ several heavy bundles of anastomosing elastic fibers pass off, to be attached to the parallel fibers of the perichondrium. Some elastic fibers apparently originate in the nodule, for t1ie fibers passing off from its anterior extremity exceed in luimber those passing into it posteriorly.
In conclusion, I agree Avith Friedrich in not considering the process
Dean D. Lewis 185
described by Gcrliardt as the processus vooalis of tlie tliyroid cartila.u^'. It may be compared to (lie other pericliondrial })rocessos by which I lie elastic tissue of tlic lai-yiix is attached to the hiryngeal cartilages at dilTcrent points. It is impossible to explain why tlie thyi'oid cartilage develops as it does, but the relation (existing between tlie ril)rous tissue occupying the concavity of ilic lamina mcdiaiia, and the clastic tissue of the ligamentnm vocah^ docs not resemble in tlic least the histological I'clations existing between the hyaline substance of the arytenoid cartilages, and their vocal processes.
I have not found cartilage cells in the nodules occupying the anterior extremities of the ligamenta vocalia. i would suggest that these nodules be known as the noduli vocales. It is difTicult to assign to these nodules their physiological function, but the inci'casc in the mnnhcr of elastic fibers and their arrangement at this point, slrengthened, as they are, by nnmerous round and spindle cells, would suggest that the ligamenta vocalia are here subjected to their greatest tension, and ai'c therefore re-inforced.
TiTK Delation of the Musculus Vocalts to the
LlOAMENTUM VOCALE.
The relation (d' the innscnliis vocalis to tlic clastic lllx'i's of the ligamcntum vocale is highly important, and although it has been studied by many anatomists and laryngologists in recent years, there is at the present time no uniformity of opinion concei'ning it, oi- its functional significance in the production or modification of higher tones.
Tjudwig"' describes the musculus thyrco-aryta>noideus as being divi(k'd into a poi-tio aryvocalis and arythyreoidca. TIk! foi'mci' division begins upon the lower extremity of the anterior surface of the arytenoid cartilage, and passes in parallel bundles by the side of the ligamentum vocale. to end in it. The shorter fibers end directly anterioi' to the apex of the vocal process; the longer near the thyroid cartilage. J"'hese fibers, acting simultaneously, draw the ligamentum vocale downward and outward. If they act independently of each other, different segments of the ligament will be affected in different ways. Fibers anterior to the insertion of the muscle are rendered tense, while the fibers posterior to it arc in^laxcd. Ludwig regards the ligamentum vocale as the tendon of the musculus thyreo-aryta^noideus.
Verson ^^ denies that any fibers of the musculus tbyi'i^o-aiTla-noideiis are inserted into the elastic fibers of the ligamentum vocale.
-' Ludwig: Lehrbuc;h der Physiologie der Menschen. Bd. i, pp. 567-570. "Verson: Beitrage z. Kenntniss des Kehlkopfes u. der Trachea. Wien, 1868, p. 3.
186 Tlio Elastic Tissue of the Human Larynx
Luschka/' after making a study of larynges in which the musculature was well developed, came to the conclusion that the muscle fibers belonging to the free border of the ligamentum vocale pass along the whole length of the ligament, retaining their muscular characteristics from the arytenoid to the thyroid cartilage. His findings in the larynges of children verified his conclusions as to the condition in the adult.
Henle '* states that the fibers of the musculus thyreo-artyrenoideus internus, adjacent to the ligamentum vocale, are small. The fibers lying nearest to the ligament pass in between the elastic fibers composing it, and are closely connected with them. A number of the mviscle fibers either arise from or end among the elastic fibers of the ligament. Eegarding the functional significance of this relation, he says that the fibers ending in the elastic tissue must have some influence upon the movements of the ligamentum vocale, and suggests that the short fibers acting upon segments of the ligament may account for the production of falsetto tones.
Jacobson '" describes the musculus thyreo-arytamoideus as having a very complicated structure. He finds, in horizontal sections, muscle fibers arising from the processus vocalis, and the lateral surface of the lower part of the arytenoid cartilage, which pass inward to the free border of the ligamentum vocale, and end in bundles of parallel elastic fibers, which eventually pass into the ligamentum vocale. He sums up his conclusions concerning these muscle fibers by saying that there can be no doubt that the musculus aryvocalis of Ludwig may be so developed in some cases, that the ligamentum vocale may be rendered tense, while the arytenoid cartilage remains stationary or in the jDOsition of adduction. Thus, the short fibers of the muscle may oppose the long fibers, which act as adductors.
Kanthack^' states that the medial fibers of the musculus thyroarytenoid eus pass between the elastic fibers and appear to end in them. In sections, which are made exactly parallel to the course of the muscle fibers, it can be seen, however, that they pass uninterruptedly from ar}^tenoid to thyroid cartilage, without ending among the elastic fibers of the ligament. The ligament is not to be regarded as the tendon of the muscle.
Friedrich '" notes that there is no definite arrangement of the elastic
"Luschka: Der Kehlkopf des Menschen. Tiibingen, 1S71, p. 121. "Henle: Handb. der Eingeweidelehre des Menschen; p. 266. "Jacobson: Arch. f. Mikr. Anat., Bonn, Bd. xxix, pp. 624-627. -'^Kanthack: Arch. f. path. Anat., etc., Berk, Bd. cxvii, p. 542. ^'Friedrich: Archiv. f. LaryngoL u. Rhinol. Bd. iv, p. 207.
Dean D. Lewis 187
fibers about the end of tlie muscle fiber. He is inclined to believe, however, that there is a close relation between the muscle fibers and the elastic elements of the cord,' and emphasizes the fact that Ijy muscle fibers leaving the body of the muscle and running for a short distance in the ligament, as fine an influence could be exerted upon the elastic elements of the ligament as could be explained by the idea of the insertion of muscle fibers directly into the elastic fibers. He does not regard the ligament as the tendon of the musculus vocalis.
Katzenstein ^ does not regard the ligamentum vocale as the tendon of the musculus vocalis. He has never seen the direct transition of muscle fiber into elastic fiber.
In horizontal and frontal sections, muscle fibers may be found, which are closely related to the elastic fibers of the ligamentum vocale. I have found these to be most numerous posteriorly, in front of the vocal process of the arytenoid cartilage. These muscle fibers have no such complicated arrangement as Jacobson depicts. They seem to pass in between the elastic fibers of the ligament, and to be surrounded by these fibers, but it is probable that they do not end among the elastic fibers of the ligament. Smirnow's investigation '" as to the mode of insertion of striated muscle into soft tissue will aid in settling this question. He says that in all eases in which striated muscle is not in direct relation to the bony or cartilaginous skeleton, in which the fibers are attached to the softer varieties of connective tissues, these tendons consist, wholly or almost wholly, of elastic tissue. In attempting to establish this relation, I have been unable to find in any case a transition of muscle fiber into elastic tissue.
The laryngoscopic findings in the production of falsetto tones as given by Stork, quoted by Jacobson, would suggest that the ligamentum vocale may act in segments. I am inclined to believe that these fibers, wdiich are so closely related to the elastic tissue of the ligamentum vocale, but still cannot l;e considered as inserting into it, may by their contraction make tense the vocal ligaments, while the arytenoid cartilage remains stationary, and may by their contraction render the production of falsetto tones possible. There is still another possibility, hoAvever. The fibers of the ligamentum vocale, as they pass forward to their anterior attachment, are re-inforced by additional elastic fibers, which are derived from the perimysium of the musculus vocalis, and through it are attached to the arytenoid cartilage. It is possible that by the contraction of muscle fibers related to these elastic elements different segments of the cord
-^Katzenstein: Arch. f. Laryngol. u. Rhinol. Bd. xiii, p. 346. -^ Smirnow: Anat. Anz., Jena. Bd. xv, p. 488.
188 The Elastic Tissue of the Iliniiau Larynx
could be acted upon, and the cord abducted and rendered tense, while the arytenoid cartilage remained in a position of adduction.
MIDDLE ZONE.
The Elastic Tissue of the Ventriculus Laryngis.
The continuation upward of the subepithelial elastic layer of the labium vocale forms the delicate elastic membrane surrounding the venti'iculus laryngis. This membrane lies just beneath the epithelium of the ventricle, and is poorly developed. Above, it becomes continuous with the elastic tissue occupying the plica ventricularis. Transverse sections through the lower part of the ventricle and through the vocal liganient show well the relation existing between the elastic fibers belonging to each at this level (Fig. 7). The elastic fibers upon the medial surface of the ventricle are continuous with the lateral fibers of the ligament. The elastic fibers upon the lateral surface of the ventricle become continuous posteriorly with the fibers of the ligament, or are attached to the antero-lateral surface of the arytenoid cartilage. Anteriorly, as they approach the nodulus vocalis, they divide, part to be inserted into the nodule and part to be reflected laterad to become continuous with the elastic fibers of the perichondrium, covering the inner surface of the thyroid cartilage.
SUPERIOR ZONE.
Aryteno-Epiglottidean Ligaments: Membrana Quadrangularis.
The elastic fibers of this zone are situated in the aryteno-epiglottidean folds. Their general direction is from above and anteriorly, downward and backward. Posteriorly, these fibers are attached to the medial surface of the arytenoid cartilages, and anteriorly, to the lateral borders of the epiglottis. Above, they pass upward to the free borders of the folds, and are related to the cartilages of Santorini and Wrisberg. Below, the fibers become thickened to form the ligaments occupying the labia ventricularia.
LiGAMENTUM VeNTRICULAEE : LiGAMENTUM ThYREOART^NOIDEUM
SUPERIUS.
Luschka describes the elastic fibers forming the ligamentum ventriculare as being grouped into well-defined bundles anteriorly and posteriorly. In the middle of their course the elastic fibers are separated from each other by numerous glands.
Dean D. Lewis 189
Verson** denies the existence of a proper ligamentum ventriculare. He states that the elastic fibers occupying the labium ventriculare have no definite direction. A section made at right angles to the labium reveals some elastic fibers which are separated from each other by numerous glands. Interspersed among the elastic fibers are numerous collagenic fibers.
Henle '^ describes the ligamenta ventricularia as arising on each side of the ligamentum thyreo-epiglotticum from a connective tissue mass, ■which fills the angle of the thyroid cartilage at this level. Anteriorly, the ligament is an independent band. Posteriorly, the fibers separate to enclose spaces, which lodge glands and fat. In the vicinity of the arytenoid cartilage, between the spina superior and inferior, a band of elastic tissue passes dovmward posterior to the ventricle. This is the ligamentum arcuatum of Tortual.
Henle's description of this ligament seems to be the most accurate. The elastic fibers arising from the angle of the thyroid cartilage unite to form a distinct ligament in their anterior third. (See Fig. 10.) The ligament is not dense, and the single fibers composing it can be readily recognized. It arises from a connective tissue mass occupying the angle of the thyroid cartilage, which is much smaller than the one at the level of the ligamenta vocalia. In the posterior two-thirds of their course the fibers composing the ligament separate from each other and enclose spaces, in which are lodged numerous glands and fat. The fibers of the ligament anastomose frequently with each other. Numerous collagenic fibers are scattered among the fibers composing the ligament.
The elastic cartilage forming the epiglottis is broken up by numerous glands. (See Fig. 11.) I have attempted to find in this elastic cartilage a definite functional arrangement of the fibers, but this has been impossible because of their number and frequent anastomoses.
The discussion as to the relation existing between the epithelium and elastic tissue of the larynx has been definitely settled by the use of specific stains. The elastic fibers are differently directed in different divisions of the larynx, and bear a different relation to the epithelium in various regions. At the level of the ligamenta vocalia the epithelial cells rest directly upon an elastic fiber layer, which is only arbitrarily separated from the elastic fibers of the ligament. The subepithelial fibers are
'"Verson: Strieker's Handb. der Lehre von den Geweben des Menschen u. der Thiere. Leipzig, 1871, p. 459.
= Henle: Handb. der Eingeweidelehre; p. 254. 14
190 The Elastic Tissue of the Human Larynx
parallel to the fibers of the ligament, and to the mucous folds found at this level. The elastic fibers enter the bases of the latter, but do not pass vertically into them. An exception to the latter statement is found upon the medial surface of the vocal process of the arytenoid cartilage, where the fibers of the subepithelial layer pass vertically or obliquely into the base of a small mucous fold. This change in direction of the elastic fibers corresponds approximately to the level at which the linea arcuata inferior of Eeinke ^^ crosses the vocal process. This line limits the extent of an oedema of the labium vocale posteriorly; the vertical arrangement of the elastic fibers probably acts as a barrier at this point. This arrangement may have some further functional import. In this region the epithelium is subject to the greatest stress, owing to the frequent and wide range of movement of the processus vocalis. The arrangement of the elastic fibers here undoubtedly anchors more securely epithelium to vocal process. Eeinke states that occasionally a similar relation between epithelium and subepithelial elastic layer is found at the level of the nodulus vocalis. I have not found this relation in my specimens. In the subglottic region the subepithelial elastic fibers are separated from the epithelium by a thin connective tissue layer. The elastic fibers are here vertically directed. The same relation is found in the inter-arytenoid space, and in the superior laryngeal zone.
I am indebted to Mr. Leonard H. Wilder, artist to the laboratory, for the accompanying drawings.
ExPLAXATio:Nr OF Plates.
PLATE I.
Fig. 1. — Frontal section through the anterior part of the conus elasticus. 1. Thyroid cartilage. 2. Elastic fibers of the conns passing mediad on each side to form the ligamentnm cricothyreoideum medium, which is pierced by the crico-thyroid vessels. Most of the fibers pass cephalad and laterad from the cricoid cartilage to attach to the thyroid cartilage. Some arise from a raphe formed by the union of the horizontal fibers of the ligament. 3. Cricoid cartilage.
Fig. 2. — Frontal section through larynx, just posterior to the anterior commissure. 1. Thyroid cartilage. 2. Cricoid cartilage. 3. Fibers of the conus elasticus. 4. Nodulus vocalis, showing the convergence of the elastic fibers of the ligamentum vocale upon its medial surface. 5. Musculus vocalis. 6. Ventriculus laryngis. 7. Ligamentum thyreo-epiglotticum. 8. Subepithelial elastic layer separated from the elastic fibers of the conus by glands and collagenic tissue.
Fig. 3. — Transverse section through the ligamentum cricothyreoideum medium, showing its relation to the fibers of the conus and the subepithelial elastic layer.
"Reinke: Fortschritte der Medicin. 1895, p. 476.
Dean D. Lewis 191
PLATE II.
Fig. 4. — Transverse sectiort through the ligamentum cricothyreoideum medium, showing the general direction of the elastic fibers composing it. Bundles of vertical fibers are surrounded by horizontal fibers, which pass toward the median line to meet corresponding fibers of the opposite side. In this section the crico-thyroid artery is seen piercing the ligament. The direction of the fibers of the subepithelial elastic layer and their relation to the ligament is shown.
Fig. 5. — Transverse section through the larynx at the lower part of the thyroid cartilage. 1. Thyroid cartilage. 2. Conus elasticus. 3. Cricoid cartilage. 4. Posterior crico-arytenoid muscle.
PLATE III.
Fig. 6. — Anterior part of preceding figure as seen under low power, showing the mode of attachment of the elastic fibers of the conus to the thyroid cartilage, and the general direction of the fibers. 1. Thyroid cartilage. 2. Perichondria! process by which the elastic fibers of the conus are attached to the cartilage. 3. Anterior part of the conus elasticus. 4. Subepithelial elastic layer.
Fig. 7. — Transverse section through the larynx at the level of the ligamenta vocalia. 1. Thyroid cartilage. 2. Perichondrial process by which the elastic fibers attach. This is the median process described by Gerhardt. 3. Nodulus vocalis (cartilaginous nodule described by Mayer). 4. Ligamentum vocale. 5. Processus vocalis of the arytenoid cartilage. 6. Arytenoid cartilage. 7. Ventricle of larynx.
PLATE IV.
Fig. 8. — Transverse section through the larynx at the level of the attachment of the anterior extremities of the ligamenta vocalia — low power. 1. Thyroid cartilage. 2. Thickened perichondrium described by Gerhardt as the processus vocalis of the thyroid cartilage. 3. Nodulus vocalis (cartilago sesamoidea anterior) ; anastomosing bundles of elastic fibers pass off from it anteriorly to be attached to the horizontal fibers of the perichondrium. 4. Parallel elastic fibers of the ligamentum vocale passing into the posterior extremity of the nodulus vocalis.
Fig. 9. — Transverse section through the anterior attachment of the ligamentum vocale. The larynx is divided in the median line. Low power: Van Gieson's picro-fuchsin. 1. Thyroid cartilage. 2. Perichondrial fibers. 3. Nodulus vocalis, showing numerous round and spindle cells. ,4. Musculus vocalis.
PLATE V.
Fig. 10. Transverse section through the larynx at the level of the ligamentum ventriculare. 1. Thyroid cartilage. 2. Cricoid cartilage. 3. Ligamentum ventriculare. 4. Fibers of the ligamentum thyreoepiglotticum. 5. Ventriculus laryngis. 6. Group of glands.
Fig. 11. — Transverse section through the epiglottis.
THE ELASTIC TISSUE OF THE HUMAN LARYNX
DEAN D. LEWIS
PLATE
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FIG. 1.
FIG. 3.
AMERICAN JOURNAL OF ANATOMY—VOL. I\
THE ELASTIC TISSUE OF THE HUMAN LARYNX
DEAN D LEWIS
PLATE II
FIG. 4.
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AMERICAN JOURNAL OF ANATOMY-VOL. IV
THE ELASTIC TISSUE OF THE HUMAN LARYNX
DEAN D. LEWIS
PLATE
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AMERICAN JOURNAL OF ANATOMY-VOL.
THE ELASTIC TISSUE OF THE HUMAN LARYNX
DEAN D. LEWIS
PLATE IV
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FIG. 9.
AMERICAN JOURNAL OF ANATOMY— VOL. IV
THE ELASTIC TISSUE OF THE HUMAN LARYNX
DEAN D. LEWIS
PLATE V
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FIG. 11.
AMERICAN JOURNAL OF ANATOMY—VOL. IV
STUDIES OF THE INTERSTITIAL CELLS OF LEYDIG. No. 2. — Their Postembryonic Development in the Pig.
R. H. WHITEHEAD, M. D.
Medical Department, University of North Carolina.
With 5 Text Figures.
In a recent article ^ I presented the results of a study of the embryonic development of the interstitial cells of Leydig in the pig. In the present article I wish to give a brief account of the findings in a study of their postembryonic development in the same animal. The methods employed were the same as those described in the first article, to which I may refer also for the more important facts in the literature of the subject.
The youngest pig in my series was one month old. In sections of the testis at this age, compared with one from the embryo pig near term, the cross-sections of seminal tubules are somewhat more numerous and closer together, and the masses of interstitial cells are proportionally smaller. Beneath the albuginea the cells are much reduced in size, and are arranged in a few more or less parallel rows, separated by small bundles of connective-tissue fibres. In the deeper portions of the gland, however, the cells are still of about the same size. Three main types of cells can be observed, as follows (Fig. 1) :
1. Cells with cytoplasm condensed around an eccentric nucleus, while the periphery is extensively vacuolated. The vacuoles have more or less uneven, ragged margins. Some of them hold inclusions which vary in size; the largest of these have the granular appearance and staining reactions of the cytoplasm, while others are more hyaline in appearance. Occasionally structures entirely similar to these inclusions are found between the cells.
2. Cells whose cytoplasm is condensed around an eccentric nucleus, while their periphery is much clearer, containing only a few scattered cytoplasmic threads.
»Amer. Jour. Anat., Vol. 3, No. 2, 1904. American Jourxal of Anatomy. — Vol. IV.
194
Studies oi" tliu Interstitial Cells of Lejdig
3. This variety is similar to the preceding, but is characterized by the presence of large acidophile granules, which have about the same size as those noted in the germinal epithelium of the early embryo. They are more granular in appearance, however, than the latter, and in preparations stained by Mallory's method they take the acid fuchsin, whereas the granules of the epithelium are stained by the aniline blue. With Mann's mixture of methyl blue and eosin they are stained by eosin. Although acidophile, they do not stain with as much intensity as the granules of eosinophile leucocytes. The granules are situated, for the most part, in the peripheral portion of the cytoplasm; occasionally a cell is found which seems loaded with them throughout, but, as a general rule, they are largest and most numerous near the periphery. No such granules were seen within the seminal tubules; in the spaces between the Leydig's cells, however, small collections of them were rather frequently encountered, which in most cases were undoubtedly small por
FlG.
Fig.
Fig. 1. Fig. 2.
Types of Leydig's cells in pig one month old. x SOO.
Pig three months old. A small group of Leydig's cells. x 800.
tions sectioned from the periphery of granule-bearing cells, but in some instances seemed to be free. All the cells of these three varieties have rather coarse, well defined cell-boundaries, especially marked in the case of the vacuolated cells. These boundaries frequently stain differently from the cytoplasm proper; in preparations stained by Mann's solution of methyl blue and eosin the cell-boundaries quite commonly are blue, while the cytoplasm takes the eosin. Many of the cells have two nuclei, but no mitotic figures were observed. A review of my preparations of the testis from the embryo just before term shows that all these varieties of cells are present there; indeed the principal difference between the two glands, so far as Leydig's cells are concerned, is the atrophy of the subalbugineal layer in the pig one month old. The granules, however,
R. H. Whitehead
195
in the granule-bearing cells of the embryonic gland are smaller and not so limited to the periphery of the cells.
In preparations stained with Sudan III or osmic acid numerous globules of fat, oftentimes very large, are found constantly in the seminal tubules; but the interstitial cells contain at the most only a few fine droplets — many of them contain no fat whatever.
The collections of cells have a rich blood-supply through a network of thin-walled capillaries. A rather striking feature in the testis at this age is the large number of eosinophile leucocytes, both in capillaries and free among the interstitial cells.
In the pig two months old Leydig's cells, in general, are smaller than in the preceding specimen. The varieties of cells described above are still present, but with some differences.
Fig. 3. Fig. 4.
Fig. 3. A small area of testis in pig one month old. x 50. Fig. 4. Small area of testis in pig five months old. x 50.
The granule-bearing cells are scanty, while the cells with pale periphery are quite abundant, as are also the vacuolated cells, the two together forming the great majority of the interstitial cells. In the case of the vacuolated cells the number of inclusions is noticeable. In many of these cells the septa between the vacuoles are breaking down.
At three months the convoluting of the seminal tubules has increased considerably, so that many more cross-sections of them are seen, and the interstitial cells are divided up into smaller collections. The breaking down of the septa between vacuoles and the concentration of cytoplasm around the nucleus have also progressed, so that now the individual cells are much smaller than in the preceding stages, and most of them present the pale periphery (Fig. 2). A very few containing acidophile granules may be seen.
lU(j studies of the Interstitial Cells of Le^alig
These two processes, growth of the tubules and atrophy of the interstitial cells, continue at such a rapid rate that in the five-months pig the tubules greatly predominate over the interstitial cells (compare Figs. 3 and 4). The latter are now so reduced in size as to almost be identical in appearance with the subalbugineal cells of the pig at one month. Individual cells are shown in Fig. 5. Many of them are like the central one in the figure, otliers entirely lack the distinct cell-boundaries and are little more than naked nuclei, and others show distinct cell-boundaries only at intervals, especially at the margin of a vacuole.
Of the three adult testes at my disposal two were evidently pathological, as the tubules in one case contained no sexual cells, and in the other only a few spermatogonia ; probably they were ectopic testes, and need not be considered here. The tliird one, however, was normal, and spermatogenesis was quite active. Sections show that the growth and convoluting of the seminal tubules have progressed still further, with the result that there are very few Leydig's cells between the albuginea and
Fig. 5. Types of Leydig's cells iu pig tive months old. x 800.
the bases of the tubules, but they have been crowded against the lines of attachment of the septa to the albuginea. In the deeper portions of the sections the general appearance of the cells is quite similar to that found in the five-months pig, with the exception that they are somewhat larger. They do not contain any acidophile granules, nor could Eeinke's crystalloids be demonstrated in them. The subdivision of the groups of Leydig's cells has increased, and in many situations there are none between adjacent tubules.
While, of course, this study does not warrant conclusions as to the function of Leydig's cells in the adult, we may at least inquire if it furnishes any data in support of any of the hypotheses which have been advanced as the result of histological investigation of adult conditions. In favor of the theory of v. Bardeleben, that Leydig's cells replace Sertoli cells as the latter are worn out in the performance of their function, I can find no evidence in any of the preparations. After the basement membrane of the tubules is laid down it forms a barrier which completely prevents the passage of interstitial cells into the tubules. So also as to the view
IL 11. Whitehead 11)7
of Phito, that the function of Leydig's cells is to store up fat and pass it on through the walls of the tubules to be used as pabulum in spermatogenesis, the evidence is negative. The Leydig's cells of the pig's testis contain little or no fat, while the tubules show large quantities of that substance; nor could 1 detect the minute canals described by him in the walls of the tubules. Moreover, if recent investigations upon fat metabolism are to be accepted, fat entering the tubules from the outside would probably pass through their walls, not as such, but rather as its two liquid components. Some support, however, might be derived for an extension of Plato's theory as suggested by v. Lenhossek, according to which the function of the interstitial cells is to store up, not merely fat, but other material as well, to be used as pabulum by the tubules. The most important facts in the development of Leydig's cells, it seems to me, are the alternating periods of hypertrophy and atrophy, and the structural characters of these cells during the stage of hypertrophy. The periods of hypertrophy precede, while those of atrophy are synchronous with, periods of rapid growth by the seminal tubules. Moreover the changes in the interstitial cells, though occupying much more time, are comparable, to some extent, with those which occur in secreting cells. So that the appearances described might be interpreted as possibly indicating that the Leydig's cells elaborate a specific pabulum for the tubules during the development of the testis.
I wish here to thank Professor F. P. Mall for the courtesy of a seat in his laboratory while this article was in preparation.
PROPHASES AND METAPHASE OF THE FIRST MATURATION SPINDLE OF ALLOLOBOPHORA FCETIDA.
BY
KATHARINE FOOT AND E. C. STROBELL, Woods Holl, Mass. With 9 Plates.
In the most mature eggs found in the ovaries of AUolohopJiora fa'tida, the germinal vesicle is intact, the large nucleolus is present and the chromosomes are not 3'et formed.
In the eggs of the freshly deposited cocoon, the first maturation spindle is at the metaphase.' From the time, therefore, that the eggs leave the ovaries, until they reach the cocoon, the prophases of the first maturation spindle take place, i. e., the forming of the chromosomes, the breaking down of the germinal vesicle, and the disappearance of the large nucleolus. In the summer of 1901, we found that these stages of development occur, while the eggs are in the reccptacula ovorum ' and we have thus far ol)served no exception to this rule.
In an earlier paper (Foot and Strobell. '02), we demonstrated that these worms deposit their cocoons about every third day, and it is therefore probable that the eggs accumulate in the receptacula during this period, indicating that the development of the eggs })i-ogresses very slowly in the rcceptacuUnn ovorum. The earliest stages shown by these eggs, have the germinal vesicle intact, with the nucleoplasm still undifferentiated into distinct chromatic and achronuitic substances, a large nucleolus with one or more vacuoles, and no indication of any centriole or rays in the cytoplasm, while the most mature eggs have the first maturation spindle at the metaphase.
' We have found only one egg in which the chromosomes are not oriented in the equator of the spindle. The normal stage of development appears to be the metaphase of the first spindle, though there are many degenerated and disintegrated eggs, some showing a vestige of a germinal vesicle but with no differentiation of the nucleoplasm, the chromatin being disintegrated and structureless, and in only one or two cases have we found even an indication of a persisting nucleolus.
^Marshall and Hurst state in their text book, "Practical Zoology" (1888), that immature eggs may be found in the receptacula ovorum of Lumbricus at certain seasons of the year. American .Journal of Anatomy. — Vol. IV.
300 First Maturation Spindle of Ailolobophora Footida
Method.
In the summer of 1901, Ave fixed and sectioned a larp-c nnml)er of reccptacula ovonnn. but we found this a very unprofitable method; accurate study of the normal egg being very much hampered by the number of abnormal eggs found in the receptacula, in some cases the entire receptaculum being filled with eggs in various stages of degeneration. We found in one receptaculum ovorum as many as forty eggs and of these only four were normal. A more- serious diflficulty was the unfavorable action of the fixative on the receptaculum as a whole. The swelling or shrinking, or the combination of both, produced by some fixatives, acts with intensified effect on the mass of eggs crowded into the receptacula, often distorting the normal eggs in a way to render them valueless for cytological study.
In the summer of 1902, Ave tried removing the eggs from the receptacula after they had been cut from the worm and placed in a watch glass in distilled AA^ater. By carefully teasing the walls of a receptaculum, under a dissecting microscope, the eggs can be pressed out, and only those that appear normal selected for stud}', the subsequent technique being the same used for eggs collected from the cocoons (Foot, '98). The folloAving fixatives Avere used, chromo-acetic, corrosive sublimate, corrosive acetic, Eabl's picro-sublimate, Boveri's picro-acetic, picro-sublimate, Flemming's chromo-aceto-osmic, and the same proportion of chromic and osmic omitting acetic acid. Hermann's platino-aceto-osmic and the same proportion of osmic and platinum chloride, omitting the acetic acid. A comparison of the photographs AA'ill shoAv that the platino-osmic has proved the least injurious to both nuclear and cytoplasmic structures. The sections Avere stained Avith iron-hffimatoxylin foUoAved by dilute Bismarck broAvn, or Avith Bismarck broAvn alone. In some cases, unstained sections give the most satisfactory photographs. This is especially true for archoplasm, AA'here in stained preparations the dense stain taken by the archoplasm produces such a strong contrast to the faintly stained cytoplasm, that it is impossible to get an accurate reproduction of one Avithout sacrificing the other. All the preparations AA^ere stained with the end in vicAv of securing satisfactory photographs, as aa'c aim to present only such cytological phenomena as can be clearly demonstrated by photography.
The impossibility of securing a clear demonstration of the prophases in fixed and sectioned eggs led us to devise a ncAv method AA'hich is a modification of the smear method. Instead of smearing a mass of eggs on the slide, Ave handle each egg separately. After isolating a liA'ing egg
Katharine Foot and E. C. Strobell 20.1
ill a very small drop of water on tlie slide, the membrane is carefully pricked with a very fine needle and as the cytoplasm flows out, the egg membrane is gently dragged away with the needle, allowing the contents of the egg to spread and dry immediately. By this method the germinal vesicle, and sometimes even the spindle, flow out of the egg membrane intact, and dry so quickly that the structures are remarkably well preserved. The vesicle when drying flattens out over a larger area, leaving the individual chromosomes or threads sufficiently separated to be clearly identified, and when the entire spindle passes out of the egg membrane intact, all the eleven chromosomes are beautifully demonstrated on one plane. In this manner we arrange from 20 to 30 eggs on a slide, which has been previously ruled with a diamond into definite areas, so that the position of each egg is known and any egg can be studied later in connection with data taken before it was killed.'
Cytoplasm. — During the development of the egg when the prophases of the first maturation spindle occur there is a marked change in the structure of the cytoplasm and during this period there is a decrease in the size of the egg and an increase in the amount of the substance between the egg membrane and the outer membrane, greatly increasing the width of the letter area. Compare the space between the two membranes shown in Photos. 13, Plate I, and 68, Plate lY, eggs at the germinal vesicle stage, and that of Photos. 99 and 100, Plate Yl, where the first maturation spindle is at the metaphase.^ We have demonstrated these two membranes in earlier papers (1897, Fig. 2) (1901, Photos. 57 and 59), and shown that AUolohophora possesses in common with many OUgochcetes, a delicate outer membrane and an equally delicate membrane in contact with the egg itself, the space between the two being filled with a relatively non-stainable substance. Yejdovsky and Mrazek have observed these two membranes with coagulated substance between them in many Lumhricidce and they criticise Gathy's interpretation of the three layers in Tuhifex as one thick membrane.
The difference of size and densitv between the eo-g-s at the terminal vesicle stage and those containing the first maturation spindle is very evident in living eggs, the latter being smaller, more dense and more opaque and these features are equally evident in the dried preparations. At the germinal vesicle stage the typical cytoplasm shows a distinct
' Such slides do not resemble smear preparations, they suggest rather slides with a few thick sections far removed from one another.
This contrast is really more marked than shown in the photographs, as Photos. 13 and 68 are magnified nearly 300 diameters more than Photo. 99.
202 First. Maturation Spindle of Allolobopliora Foeticla
honey-comb structure and at the spindle stage there are fewer alveoli and those present are much smaller. The increase in the amount of substance between the inner and outer membranes of the egg and decrease in the number and size of the alveoli, suggest that the former may be increased at the expense of the latter, but we have no proof of this.
Osmopliih Granules. — Typical osmophile granules in the cytoplasm of nornuil eggs found in the receptaculum ovoriim are demonstrated in the unstained sections of Photos. 68 and 69, Plate IV. A comparison of these sections with the ovarian eggs of Plate 42 of an earlier paper (1901) shows a diminution in the amount of osmophile substance in these older oocytes. In the above mentioned paper we noted a decrease in the amount of osmophile substance between the ovarian and the cocoon eggs and suggested that the storing. of the osmophile substance in the ovarian egg must be for the use of the egg from the time it leaves the ovary until it is supplied with the nutritive albumen of the cocoon, i. e., during the prophases of the first maturation spindle. This supposition seems confirmed now that w^e know these processes go on very slowly in the receptacula ovorum and that the osmophile substance gradually diminishes in amount during this period.
We first demonstrated these osmophile (deutoplasmic) granules in 1898, and in subsequent papers have presented additional data. "\Ye have shown that they are not dissolved out of the cell by either turpentine or xylol, but that after staining they are as a rule invisible, having lost all trace of the blackening caused by the osmic acid. This also fades in unstained eggs that have been kept for a long time in paraffine or mounted in balsam. If a section is photographed before staining, Plate IV, Photos. 68 and 69, and then stained in iron hoematoxylin the granules are indistinguishable even with a 3 mm. lens, but if the section is compared with a photograph of the unstained preparation that shows exactly where to look for each granule, they can be identified as clear, colorless bodies that would entirely escape observation without the photograph as a guide.
Centriole and Spindle. — In this paper we shall adopt Boveri's term centriole for the small central granule of the asters for which in an earlier paper we retained the old term centrosome. We drop the term centrosome for this granule not because we find a second body in the asters of Allolohophora which answers to the centrosome of Boveri and others, but to avoid the confusion of retaining an old term which implies a structure and accompanying complicated changes Avhich we have not found in this egg.
The centrioles destined for the two poles of the first maturation
Katharine Foot and E. C. Strobell 203
spindle are first seen at opposite poles of the germinal vesicle, indicating that the}' arise independently and not by division of a primary centriole. This stage is shown in Photos. 81, 82, 84 and 86, Plate V. The eggs of Photos. 81 and 82 are greatly marred by poor fixation, chromo-acetic being as harmful to cytoplasm as it is to nuclear structure (see p. 215). The centriole of each aster is so small that only the presence of the rays justifies our interpreting the central microsome as the centriole. In Photo. 81, Plate V, the centriole is in contact with the membrane of the germinal vesicle, and in Photo. 82, Plate V, only slightly removed from it. The two asters are at opposite sides of the germinal vesicle, being separated by fifteen sections, the entire germinal vesicle being cut into ninteen sections. In all these sections the membrane of the germinal vesicle is intact and at the points where the rays of the asters focus the membrane slightly protrudes."
It might be claimed that the theory of the nuclear origin of the centriole is supported by the presence of these two centrioles almost within the germinal vesicle, but they certainly do not support the particular phase of the theory that holds the nucleolus responsible for the centriole, for in this egg the nucleolus is still intact and is found two sections removed from one aster and thirteen sections from the other. The injurious action of chromo-acetic on the nucleoplasm of the germinal vesicle does not always affect its membrane, although it breaks the connection between the two, leaving the membrane in contact with the surrounding cytoplasm, this being favorable for the identification of the earliest appearance of the centriole. On the contrary other photographs show that many fixatives favorable for the study of nuclear constituents are of no value for studying the early appearance of the centrioles, the cytoplasm being torn away from the germinal vesicle, destroying all trace of the centrioles and asters (Photos. 22 to 25, 29 and 30, Plate II, 4G to ■49, 51 and 52, 59 to 63, and 65, Plate III). In a few cases we have found eggs killed in these same fixatives showing an equal shrinkage of cytoplasm and nucleus leaving the membrane in continuity with cytoplasm and nuclear reticulum, but the exceptions are very rare and have not been at the stage to throw any light on the origin of the centrioles. Platinoosmic, as stated above (p. 200), appears to be the least injurious for all constituents, and we hope its further use will enable us to collect more
'^ The blurred effect of the part of the membrane seen in the photographs is due to its being on a different plane from the centrioles. The two sections shown in Photos. 81 and 82 are cut so close to the periphery of the germinal vesicle that part of its membrane is seen en face. In the sections beyond those photographed, the membrane is the only part of the germinal vesicle left.
204 First Maturation Spindle of Allolobopliora Foctida
satisfactory data as to the origin of the centriolcs of the first maturation spindle.
i\[eves", '02, observations as to the constancy in size of the centrioles, regardless of the size of the cells are supported by this egg. There is an insignificant difference in size between the centrioles at the metaphase of the first maturation spindle (Photos. 26, Plate II, 91, 92a and b, Plate V, 99, 100, 101, 102 and 106, Plate VI), the second maturation spindle (Photos. 103, 104, 105, 108 and 109), the first, second (Photo. 110), and third cleavage spindles (Photo. 107, Plate VI). ' There are often exceptions to this rule, but in many of these cases the cause is obviously overstaining (Photo. 83, Plate V), for centrioles that we have seen or photographed in unstained preparations, as a rule, show no more variation in size than can be accounted for by different fixation, or individual variations. Photos. 92a and b, Plate V, show also a similarity in size of the centrioles of the peripheral and inner poles of the first maturation si3indle. There is, however, a dissimilarity in size between the centrioles of the prophases and metaphases of the first maturation spindle, the former being smaller, indicating that the centriole passes through stages of growth (comj)are the centrioles of Photos. 81, 82, 84 and S6, Plate V, with those of the metaphase, Plate VI). That centrioles are sometimes found out of the center of the sphere is probably due to fixation, for if fixation can produce such marked variations of cytoplasmic and nuclear structures as demonstrated in these photographs, it is indeed remarkable that the central position of the centriole is maintained as constantly as v^e find it in these eggs.
The first maturation spindle can be readily identified in the living egg. In Photos. 125, 128, 129 and 130, Plate IX, we see spindles that have retained their form after the contents of a living egg has been pressed out of its membrane and allowed to dry quickly on a slide. In such preparations we have found no trace of a centriole, but we cannot give much weight to this evidence for in all fixed material, both stained and unstained, a centriole is invariably present at each pole. Unstained centrioles are demonstrated in the spindles of Photos. 91 and 99, Plates V and VI, and stained centrioles in the spindles of Photos. 26, Plate II, 92a and b, Plate V, and Photos. 100 to 110, Plate VI.
Photos. 84 to 89, Plate V, suggest that a large part of the spindle is formed of achromatic nucleoplasm. In Photos. 86 to 89 a part of the membrane of the germinal vesicle is still seen and the nucleoplasm within
«The magnification of Photos. 99, 102, 108 and 110 is 710 diameters, and Photos. 26 and 109, 1100 diameters. All the others are 1000 diameters.
Katharine Foot aud E. C. StrobcU 205
this area is unmistakably assuming the form characteristic of spindle fibers. Photos. 81, 82, 83, 84 and 86, Plate Y, indicate with equal clearness that the cytoplasm contributes to the polar rays. These photographs (84 and 86) suggest a very close if not causal relation between centriole and spindle and may be called in evidence to support the theory that the spindle is formed under the influence of the centrioles. In these preparations the chromosomes certainly do not influence the form of the spindle, for although they are all massed on one side, yet the spindle remains symmetrical in relation to the centrioles. Even if this massing of the chromosomes in one-half of the spindle is not the normal condition it should produce an abnormal and distorted spindle, if the rays were formed only in relation to the chromosomes. "We are forced to conclude, therefore, that the spindle is a life expression of the nucleoplasm and jjolar cytoplasm, or is formed under the influence of the centrioles.
Nucleolus. — In a comprehensive history of the nucleolus, Montgomery, '98, shows what a bewildering number of conflicting interpretations have accumulated around this structure since it was first figured by Fontana, in 1781, and what little progress has been made in solving the problems of its significance, even its morphology being enveloped in a mass of contradictory evidence. We hope to be able to establish the morphology of the nucleolus of the egg of AHolohophora foetida by a careful comparative study of its form after killing in a variety of fixatives, by a study of the living egg, and of the dried germinal vesicles, as obtained by the method described on p. 200, We are convinced that its variety in form can be best appreciated when demonstrated by a number of photographs and with sufficient data for each fixative it may be possible to arrive at a correct decision between the artificial and the normal structures.
The germinal vesicle of AHolohophora in common with many other forms contains two distinct kinds of nucleolar formations, and for these we shall adopt Flemming's term, principal and accessory nucleoli. The former is the relatively large nucleolus which has persisted and increased in size since its first appearance in the smallest oocyte of the ovary and is peculiarly the nucleolus of the oocyte first order. The accessory nucleoli are first seen in the large ovarian eggs, and the earliest stage at which we find them they are very small and in close proximity to the chromatin (Photos. 9, 11, Plate I, 23, Plate II, and 49, Plate III), and after many fixatives stain like the chromatin. The two structures, the principal nucleolus and the accessory nucleolus, differ in several respects, as a rule only one of the former is present in a germinal vesicle (Photos. 15
206 First Maturation Spindle of Allolobophora Foctida
4, 7, 13, Plate I, 32, 37, 29, 31, Plate II, 49, 50, 58, 60, Plate III, 71, Plato IV), whereas the accessory nucleoli vary in number from one to six or more.' The principal nucleolus is composed of two substances differing in density and producing, though not invariably, the so-called vacuolated appearance, whereas the accessory nucleoli are dense homogeneous bodies and are, as a rule, not vacuolated. The principal nwlcohis and the accessory nucleoli are clearly seen in unstained sections, even the smallest of the accessory nucleoli appearing homogeneous and refractive. In Photos. 23, 29, 39, 40, Plate II, 56, Plate III, both kinds of nucleoli are shown in the same section of a germinal vesicle. Photos. 3 and 4 show two sections of the same germinal vesicle, the former containing the accessory nucleolus and the latter the principal nucleolus. Photos. 6, 7, 8 and 9 are sections of one germinal vesicle, Photos. 7 and 8 showing the principal nucleolus and Photos. 6, 8, 9 showing each one accessory nucleolus. After certain fixatives, e. g., platino-osmic, the principal nucleolus stains very faintly with iron heematoxylin and can be readily decolored, whereas the accessory nucleoli retain the hsematoxylin with as much tenacity as do the chromosomes.* The principal nucleolus disappears before the first maturation spindle is formed, whereas the accessory nucleoli often persist as late as the metaphase of the first maturation spindle. They do not always persist, however, until this period, and when they are present, their position is most inconstant, some, times being within the area of the spindle, even at the equator, but more often in the cytoplasm at different distances from the spindle. The presence of the persisting nucleoli was noted and figured in an earlier paper (Foot, '94), but at that time we had not recognized them as accessory nucleoli but supposed them to be fragments of the large egg nucleolus.
In unstained sections the so-called vacuoles of the principal nucleolus are entirely transparent and sharply differentiated from the rest of the nucleolus which is dense and refractive (Photos. 14b, 15 to 21, Plate I, 35, 39, 40, Plate II, and 74, Plate IV). Stained preparations, however,
' This applies to sections. In all dried germinal vesicles that appear to be normal, we find as a rule only one accessory nucleolus, though we have sometimes found two (Photo. 115, Plate VII), rarely three, and in one or two cases five. Sections of fixed eggs indicate that the single accessory 7iucleolus probably owes its origin to the fusing of several small ones.
'^ That the principal nucleolus fails to stain readily at these stages when the accessory nucleolus stains very intensely may be due to the disintegration of the former, for at an earlier stage of development the principal nucleolus stains intensely.
Kntliarine Foot and E. C. Strobell 207
show that nianv of tlie vacuoles contain a substance which after some fixatives can be so densch' stained that the entire nucleohis appears homogeneous, these results su})portino- the observations of investigators who claim that the so-called vacuoles of the nucleolus contain a fluid substance. In dried germinal vesicles we have not been able to demonstrate any vacuoles in the nucleolus, but in the living egg we have sometimes seen a single vacuole in the principal nucleolus. In one case the nucleolus at first showed no vacuole, one app(>aring about five minutes after the egg was under observation and persisting until the egg died. In other eggs the large nucleolus at first contained a vacuole which disappeared in about five minutes, this condition persisting until the egg died. It Avould seem, therefore, that vacuoles in the principal nucleolus of living eggs appear and disappear as maintained by some authors.
3Iany of ]Montgomery's figures sliow the vacuole stained in differential colors, but his interpretation that they " are derived from the small fluid globules which flrst appear in the .nuclear sap " is not supported by Allolohophora. Photo. 57, Plate III, might be forced to such an interpretation, but in the light of more than fifty other negative examples it must be interpreted with them as merely another expression of the effect of fixation and dehydration on the more fluid portion of the nucleolus. Even unstained preparations show that the refractive parts of the principal nucleolus and its vaciioles represent two substances of very different degrees of density and this must produce an unstable condition which is very readily disturbed by fixatives, and must be, therefore, largely responsible for the great variety of forms seen in fixed material.
The vacuoles in the principal nucleolus of Allolohopliora sometimes appear to be true vacuoles and again they appear to be a thin fluid substance which can be stained so as to completely obliterate the vacuoles (see Photos. 22 and 27, Plate II), which will reappear after decoloring as shown in Photos. 37, 42, Plate II, 49, 53, 54, 58, 60, Plate III, etc., and again the contents of many ring-like nucleoli closely resemble the surrounding nucleoplasm suggesting that it has been artificially forced into the nucleolus. This condition is shown in Photos. 36, 38, 43, 44, 45, Plate II, 50, Plate III, 79, Plate IV, 93, 94, 95, 96, and 98b, Plate Y, and many of these resemble the nucleoli figured by Coe, '99, in Cerehratulus. In some cases, e. g., Photo. 50, Plate III, it is clearly seen that a substance is massed in the nucleolus at the expense of the surrounding nucleoplasm, and Photo. 9Sa and b, Plate V, show a distinct break in the nucleolar ring indicating how the fluid portions of the nucleolus and the nucleoplasm may be brought into contact. Many nucleoli which are
208 First Maturation Spinrllo of Allolobopliora Footida
not vacuolated, contain small dark specks (see Photos. 5 and 14a) wliicli can be clearly seen and ])hotograplied in unstained preparations, for they are quite as black as the osmophile granules (see Photos. G8 and G9, Plate lY, for these granules). They differ from osmophile granules, however, in retaining their original color after staining with iron ha^matoxylin. Photo. 14a shows them in an unstained, and Photo. 5 in a stained preparation, those of the latter were clearly seen and photographed l^efore the nucleolus was stained. In 1888 Vejdovsky figured and described two nucleoli containing granules in the germinal vesicle of Rhynchelmis (Taf III) and Montgomery in '98, figured dark granules in several nucleoli, e. g., Figs. 267 to 269, but they cannot be the same as those shown in our Photos. 5 and 14a, for Montgomery finds by change of focus these dark granules can be transposed into small, clear vacuoles. Photo. 14a demonstrates that this is not the case for Allolobopliora, in this photograph some of the granules are out of focus, not all being on the same plane, yet none of them appear as vacuoles. Photo. 14b is a nucleolus from the same preparation as 14a and shows some of the vacuoles quite as small as the black granules of 14a, but a change of focus on these small vacuoles does not transpose them into granules. The granules in 14a may represent an early stage of degeneration, a later stage being shown in Photo. 75, Plate IV.
The sixty photographs of nucleoli, shown in our plates, represent forms figured by investigators for widely different material. These photographs show not only the varying forms of the so-called vacuoles, but Photo. 4 shows a nucleolus sharply differentiated into the so-called chromatic and achromatic portions, which can be differentially stained, and have been described under a variety of names. Among later papers, such a differentiation of the nucleolus has been demonstrated in Helix by Ancel, '02, and in Teleosieans by Stephan, '02. Photos. 20, Plate I, 54, 55, 60, Plate III and 77, Plate IV, show the so-called nucleololus, or endonucleolus, which Montgomer}^ and others pronounce an artefact.
It is impossible to determine how many of the fantastic forms assumed by the nucleolus of AUolohophora are artefacts, but the fact that definite forms appear more or less constantly after certain fixatives creates a wellfounded suspicion of every form that cannot be verified by comparison with the living egg.
In AUolohophora there appears to be no fundamental difference between the principal nucleolus and the accessory nucleoli, and may not the individualities of the former be due merely to its adaptation to special needs of the egg during its growth period ?
In many points the accessory nucleolus corresponds to the nucleoli of
Katharine Foot and E. C. Strobell 209
the male and female pronucleus. In the vesicles formed at the telophase of the second maturation spindle " a small dense homogeneous nucleolus is first seen in close proximity to each chromosome (Foot and Strobell, 'oo). These increase in size by groAvth and by irregular and inconstant fusing with one another. Thus in the resting female pronucleus we find nucleoli, Avhich like the accessory nucleoli are inconstant in size and number, and this inconstancy is true also for the nucleoli of the male pronucleus. One or several of these may persist until the metaphase of the first cleavage spindle and like the accessory nucleoli may be in the spindle or in the surrounding cytoplasm. These, like the accessory nucleoli, are relatively dense homogeneous structures as compared with the large nucleolus of the oocyte first order, and these points of agreement suggest the possibility of a closer relationship — may not the accessory nucleoli of the germinal vesicle arise in connection with the chromosomes of the first spindle before instead of after their division? If, as held by a number of investigators, the chromosomes of one divi-jion are in some manner related to the nucleolar substance of the following rest stage, may not this be established at an earlier period and the accessory nucleoli of the germinal vesicle be a precocious appearance of the nucleoli which are so conspicuously absent between the first and second spindles ? — the processes involved in the rest stage occurring before instead of after the first division, the origin and growth of the accessory nucleolus being part of them. The second division precociously foreshadowed in the four part chromosomes of the germinal vesicle suggests a precedent for this interpretation.
If our interpretation of the accessory nucleolus is correct, a like structure should be present in spermatocytes, and there should be two nucleoli in the spermatocyte first order in all cases where a resting stage is omitted between the first and second division. Such a condition is figured by Vom Eath, '92, in Gryllotalpha. His Figs. 10 and 11 show two nucleoli in the spermatocyte first order at the spireme stage in which they are conspicuous also in AUolohopliora, and it is significant and interesting that the two nucleoli in the spermatocyte are nearly equal in size. See also Schreiners, '04, Figs. 23 and 24.
"The transformation of the chromosomes into vesicles at the telophase of the second maturation spindle was first seen in RJiynchelmis and described and figured by Vejdovsky in 1887. Our Photo. 32 shows one of these vesicles in a second maturation spindle and indicates that their formation is not necessarily dependent upon a definite form or position of the chromosomes, as this vesicle is formed before the telophase, and the chromosomes have not assumed the shape they usually show, when at the lower pole of the spindle, prior to the formation of the vesicles (Foot & Strobell, '00, Photo. 24).
210 First IMaturation Spindle of Allolobophora Foetida
We hesitate to interpret the accessory chromosome of some authors as the equivalent of the accessory nucleolus, but it is a suggestive fact that many investigators have interpreted this structure as a nucleolus and there is a significant disagreement as to whether it divides in the first or second spindles, or in fact whether it divides at all. Our interpretation that the accessory nucleolus of Allolobophora is the true nucleolus of the oocyte second order supports Wilson's, '96, surmise that the accessory nucleoli of egg cells "perhaps correspond to the true nucleoli of tissue cells (p. 93), though he bases this conclusion on his interpretation that the principal nucleolus does not correspond to the " true nucleoli of tissue cells." " He mentions two kinds of nucleoli in Qgg cells, the "principal nucleolus," or net knot, and the "accessory nucleoli," which are of the second (smaller) type, and although they do not agree in their affinity for stains with the accessory nucleoli of Allolohophora (which at this stage stain with greater intensity than the principal nucleolus and retain the color with more tenacity even than the chromosomes), they do agree in other more essential points, i. e., in their relation to the single large nucleolus as to size, number, advent and persistence. In a later edition of " The Cell " ('00) , Wilson's conclusions are greatly modified and he states that the principal and accessory nucleoli " differ widely in staining reactions, but it does not 3^et clearly appear whether they definitely correspond to the plasmosomes and karyosomes of tissue cells." He further says that the principal nucleolus " cannot be directly compared to the net knots or karyoso\nes of tissue cells," leaving the implication that they resemble the true nucleoli (plasmosomes) of tissue cells, although he adds that in color reaction the accessory nucleoli are comparable to these, pp. 127 and 128.
In Cliaiopterus, Mead, '98, figures a ring-shaped nucleolus (Fig. 6) closely resembling those of Allolohophora, and although he says nothing of accessory nucleoli he has demonstrated in several of his figures two or three nucleoli which appear to answer to the accessory nucleoli of Allolohophora. He says the nucleolus " breaks up into a number of pieces which remain for a time in the vicinity of the spindle, but gradually degenerate and disappear," p. 196. In Allolohophora it is the accessory nucleoli which often persist until after the first maturation spindle is formed, the principal nucleolus disappearing at an earlier period.
10 << Prom its staining-reaction this type of nucleolus appears to correspond, in a chemical sense, not with the ' true nucleoli ' of tissue cells, but with the net knots or karyosomes, such as the nucleoli of nerve cells and of many gland cells and epithelial cells," p. 92.
Katharine Foot and E. C. Strobell 211
Wheeler in Myzostoma, '97, finds that the nucleolus persists in some cases later than the second cleavage but he does not identify any accessory nucleoli.
The accessory nucleolus of AlJolohopliora probably corresponds to the second nucleolus, Gatliy, '00, describes in Tub if ex as arising independently and disappearing later than the first. Gathy, however, does not interpret the nucleolus he sometimes finds persisting until the metaphase of the first spindle as the above mentioned second nucleolus. His description of the gradual disappearance of the nucleoli without fragmentation is supported by our observations on the principal nucleolus of dried germinal vesicles (Photos. 121, 122, 123 and 12-4, Plate VIII), though after fixatives the nucleolus is sometimes seen breaking up into fragments (Photos. 20, Plate I, 31, 39, 41, Plate II, 54, 55, 57, 67, Plate III, 75, Plate IV and 97, Plate V). Dried preparations clearly demonstrate that the principal nucleolus gradually loses its capacity to stain, decreases in size and -finally disappears while the membrane (rf the germinal vesicle is still intact (Photos. 114, Plate VII, 121 to 124, Plate VIII). It does not pass out into the cytoplasm there to degenerate as observed in oocytes in many other forms. This suggests that its functional value is confined to the nucleus, and if our interpretation is correct that there is no fundamental difference between the principal nucleolus and the accessory nucleolus we cannot accord any special significance to the fact that the accessory nucleolus, unlike the principal nucleolus, persists in the cytoplasm before its final disappearance. Its cytoplasmic destiny may be due merely to the fact of its later origin and consequently later disappearance, i. e., after the germinal vesicle has been replaced by the spindle. Dried germinal vesicles indicate that a single accessory nucleolus is typical of normal oocytes. Sections of fixed eggs indicate that the single accessory nucleolus owes its origin to the fusing of several smaller ones.
Many authors have recognized a more or less radical difference between the large nucleolus of the germinal vesicles and the nucleoli of the cleavage stages, AlJolohopliora does not show the difference between the two nucleoli that Korschelt, '95, indicates for Ophryotroclia. In both Annelids the large nucleolus contributes nothing to the formation of the chromosomes, but in Ophryotroclia the cleavage nucleoli " vielleicht ein Theil des vorher im Kernkorper niedergelegten Ghromatins dem Kernfaden beigefiigt wird."' He adds '•' Was die erwahnten Verschiedenheiten des verhaltens der nucleolen in dem Ei- und Embryonalzellen betrifft so liessen sich diese vielleicht durch die recht verschiedenartige
213 First Maturation Spindle of Allolobophora Foctida
Aiisbildung mid Funktion dcr Kerne in den Beiderlei Zellen erkliiren, p. 5T9.
There has been a recent revival of interest in the theory that the chromatin destined for the chromosomes of the first maturation spindle is stored at an earlier stage in one or several nucleoli. In a recent paper Blackman, '03, sums up the weight of authority for this view/' and to his list of authors may be added recent papers by Goldschmidt, '02, Hartmann, '02, Bryce, '01, and especially Le Brun, '01, '02, whose extensive publications on the maturation stages of Batrachians are illustrated by many figures demonstrating this point. The evidence furnished by the egg of AUoJohophora cannot be interpreted as a support for the above theory. It must unquestionably be classed as supporting the interpretation of the many authors who claim that the chromatin destined for the chromosomes of the spindle is at no time aggregated into a large nucleolus. In Allolohophora the chromosomes are formed by a gradual segregation of the chromatin which is dispersed throughout the germinal vesicle, and in order to maintain the theory that the nucleolus is the storehouse of the chromatin there should be a definite and constant relation between the formation of the chromosomes and the breaking down and disappearance of the nucleolus. This, however, is not the case in Allolohophora, the two processes do not invariably occur in unison. If the chromosomes have their origin in the nucleolus Ave should never find the chromosomes formed while the nucleolus is intact — before it shows any evidence of breaking down. Photos. 37 and 38, Plate II, 51 and 53, Plate III, and 68 to 73, Plate IV, demonstrate that the chromosomes can be formed in the germinal vesicle Avithout any marked morphological disturbance of the nucleolus, these nucleoli not differing essentially from those of the ovarian eggs and from the nucleoli of those eggs in the receptaculum ovorum in which the chromosomes are still unformed. This is demonstrated also in the dried germinal vesicles. In Photos. Ill and 113 to 115, Plate A^II, the chromatic spireme is formed and the principal nucleolus is still intact, showing no evidence of having contributed to the chromatin of the spireme; and in those cases in which the large nucleolus loses in staining capacity, while the chromosomes increase in staining capacity, the phenomenon is probably due to the normal disintegration of the former, and not to a contribution of its substance to the chromosomes. As a rule the principal nucleolus has disappeared, or is in process of disappearing when the
" " Blachmann, Carnoy, Davidhoff, Hermann, Holl, Sobotta, R. Hertwig, Wilson and others,' p. 197.
Kathariue Foot and E. C. Strobell 213
chromosomes are formed, e. g., Photos. 121 to 124, Plate VIII, but Photos. 116 to 118, Plates VII and VIII demonstrate that the disappearance of the principal nucleolus may be retarded until after the complete formation of the chromosomes. Such cases demonstrate that the chromosomes in Allolohophora are not formed at the expense of the nucleolus. Korschelt, '95, has reached a like conclusion for the Annelid Opliryotroclia and in its morpholog}^ the large nucleolus of Opliryoiroclia is strikingly like the large nucleolus of Allolohophora (compare Korschelt's figures of the germinal vesicle 72, 74, 75 and 79 with our Photos. 29, Plate 11, 49, 58, Plate III). On this point observations on a number of Annelids are in accord (compare Myzostoma, Wheeler's Figs. 3 and 4, '97, TJialasscma, Griffin's Figs. 3, 6 and 8, '99). In Batracliians, Lubosh, '02, has supported his criticism of the nucleolar origin of the chromosomes by a reproduction of many interesting photographs of the nucleoli in Triton eggs. A few of them resemble those of Allolohophora, cf. his Photo. 8 with our Photos. 5, 14a, and 75, Plate IV, also his Photos. 5 and 18 with our 20, Plate I, 54 and 55, Plate III.
Chromatix. a Comparative Study of Sections and of Entire Germinal A'esicles dried on the. Slide.
The photographs of the germinal vesicles of Plates I to IV show the average results obtained by sectioning these eggs after killing them in the ^ ariety of fixatives given on jj. 200.
The photographs of Plates VII, VIII and IX show the average results obtained by drying individual germinal vesicles on the slide, according to the method described on p. 200. A comparison of these two sets of photographs demonstrates the advantage of the latter method, the former proving inadequate almost to the point of being misleading, and it is here evident that we have not yet found a fixative for this egg that shows the development of the chromosomes as clearly as they are demonstrated in dried preparations.
In sections, the chromatin of the most mature eggs of the ovary and of the youngest eggs of the receptacula ovorum, is at about the same stage of development, the relatively achromatic reticulum of the germinal vesicle showing only indefinite chromatic aggregations wliich appear to be the first steps towards forming the filaments out of which the eleven bivalent chromosomes are finally formed. The first indications of chromatic filaments are shown in Photos. 1 to 9, and 31, Plate II, and 60. Plate III.
In dried germinal vesicles an early stage of the aggregation of chro
214 First J\Iatunitioii Spindle of Allolobophora Fcieticla
matin is shown in Plioto. Ill, Plate YII, where the germinal vesicle is traversed l)v an extremely delicate chromatic thread or threads. Prior to this stage we have found no structure in the germinal vesicles other than the nucleoli, the entire nucleoplasm being uniformly chromatic and obscuring all differentiation. The only indication of the presence of the diffused chromatin being expressed by the fact that the nucleoplasm reacts to nuclear stains with much more intensity than it does after its chromatin constituent has formed the spireme or chromosomes.
This is true of eggs taken from the free end of the ovary, and the earliest stages of those found in the receptacula. A comparison of results obtained from dried germinal vesicles with sections creates the suspicion that much of the structure seen in sections of these eggs in the earlier stage may be due to fixation. Such artificial demonstration of the chromatin is, however, instructive in showing how the accessory nucleoli arise in close connection with the chromatin in widely separated areas of the germinal vesicles, later fusing into the one accessory nucleolus typical of later stages.
In sections, a more marked aggregation of the chromatin into' pronounced chromatic filaments is shown in Photos. 22 to 25, Plate II, 46 to 49 and 59 to 62, Plate III, these filaments undoubtedly corresponding to portions of the skeins shown in the dried germinal vesicles of Photos. 113 to 115, Plate VII.
At the upper, right-hand periphery of the germinal vesicle of Photo. 30, Plats II, there are two isolated, loosely granular filaments, the granules perhaps representing individual chromomeres, which are obscured in the more dense chromosomes of Photos. 28, Plate II, 51, 52 and 64, Plate III. Later stages of chromosome formations are shown in Photos. 68 to 72, Plate IV, and further stages of development in Photos. 85 to 89, Plate V.
In dried germinal vesicles we see a much more intelligible evolution of the chromosomes, — in Photos. 113 to 115, Plate VII, the delicate chromatic thread or threads of Photo. Ill have contracted or fused into a relatively thick spireme. This spireme divides transversely into bivalent chromosomes, the character of each chromosome being clearly expressed by transverse constrictions in the center, demonstrating that each bivalent chromosome is composed of two equal parts. Photos. 114 and 115, Plate VII, show a distinct longitudinal split of the spireme, and Photos. 116, 117, 119 to 130, Plates VII to IX, show the persistence of this split to the chromosome stage, producing tyj)ical tetrads.
In all our sections showing the stages represented in Photos. 68 to 70,
Katharine Foot and E. C. Strobell 215
Plate IV, 86 to 89, Plate V, we find the chromosomes in a tangled condition, and we are iniable to identify- in such confused masses of chromosomes the rings or other forms of an earlier stage (Photos. 51 and 52, Plate III). Presumably the small ring of Photo. 52 answers to the small four part chromosome of Photo. 72, Plate IV, and perhaps to the small chromosome of Photos. 33, Plate II, 91, Plate V, and 99, Plate VI, but our sections give no proof of this, chromosomes being so rarely isolated in fixed material that no trustworthy comparison of progressive stages can be made.
In dried germinal vesicles, however, the chromosomes of each stage are clearly isolated and can be readily compared and a few of the chromosomes of the first maturation spindle can be identified in the prophases, though their individual differences are not sufficiently marked to make such identification conclusive.
In the majority of cases the photographs of sections show that the chromatic filaments are partly formed, more or less at the expense of the reticnlum in which they are iml^edded (Photos. 22 to 25, Plate II, 46 to 49 and 59 to 62, Plate III). We are convinced that this is not comparable to the living condition; but due to fixation, for its degree varies with different fixatives. Eggs fixed in chromo-acetic show the extent to which this process can be carried, the achromatic substance " and chromatin being coagulated into thick, loose coils that are so dense they hold the stains with as much tenacity as the chromosomes (see Photo. 34, Plate II). This photograph also shows the nuclear membrane distorted and torn, whereas the membrane of the germinal vesicles of eggs killed in platino-osmic remains unbroken and in perfect contact with the nucleoplasm as well as the cytoplasm. Compare for example. Photo. 34, Plate II, with Photos, 68 and 69, Plate IV, the latter egg showing the smooth contour of the memljrane typical of a living egg, and this is also shown in germinal vesicles dried on the slide.
All the sections of germinal vesicles are photographed at the same magnification (1000) and a comparison of any of them with Photo. 34, Plate II, demonstrates the swelling of the germinal vesicles in the chromo-acetic preparation. Watching the effect of chromo-acetic on the living egg under the microscope shows that this fixative first swells the ^gg before the usual shrinkage of dehydration commences — the final shrinkage being less than that of many other fixatives. The actual size
^= "We use the expression achromatic substance because it is so well established as a definite part of the nucleoplasm as distinct from chromatin. It is often, however, a misnomer, for in some cases it stains intensely (Photos. 27 and 28, etc.).
216 First ^Maturation Spindle of Allolobophora Foetida
of the germinal vesicle of Photo. 3-1 more nearly approaches that of the living egg; but the distortion of the nuclear constituents indicates the injurious elfects produced by the chromo-acetic, probably due largely to 'the initial swelling. Snch definite and varying response to fixatives serves to support the present skeptical attitude towards all cellular structure seen h\ fixed material. The reticulum which must represent the residuum of the achromatic substance after its dehydration, presents a varied aspect, definite fixatives being responsible for definite forms. These form differences are clearly seen by a comparison of the reticulum in Photos-. 68 to 73, Plate IV (fixed in platino-osmic) with those of Photos. 51 and 52, Plate III, showing an egg of nearly the same stage of development, but fixed in corrosive sublimate. The achromatic substance of the former (Photos. 68 to 73, Plate IV), is a relatively transparent homogeneous substance in which the chromosomes are imbedded, while that of Photos. 51 and 53, Plate III, is a distinct network. The characteristics of the achromatin of the first egg (Photos. 68 to 73) are as pronounced in the unstained sections (Photos. 68 and 69) as in those stained Avith iron hematoxylin (Photos. 70 to 73, Plate IV), and this egg shows that dehydration and shrinkage have taken place with much less distortion of the nuclear and cytoplasmic elements. The nuclear membrane is intact and the cytoplasm is not torn away from the nucleus as is the case in corrosive sublimate preparations, and in all these eggs killed in fixatives containing acetic acid "^—compare those of Plates II and III with Plates I and IV. The extent to which a fixative may distort the nucleoplasm is seen in Photo. 34,
The photographs demonstrate that apart from the nucleoli only two constitutents are clearly differentiated in the germinal vesicle, the relatively achromatic substance and the sharply chromatic filaments, which, as stated above, appear to be not pure chromatin but chromatin plus a part of the achromatic substance. Photos. 22 to 25, Plate II, 46, 47 and 59 to 62, Plate III, show in many cases clear areas around the filament indicating that the chromatic filaments are partly formed at the expense of the surrounding reticulum, and the fact that after some fixatives, (e. g., chromo-acetic. Photo. 34, Plate II)-, all the achromatic substance and chromatin are welded together, suggest that the fixative may be responsible even in those cases where only a small part of the achromatic sub?tance contributes to the chromatic filament. This has a distinct bearing on the theory that only a small part of the chromatin of
" Tellyesniczky's, '02, criticism of the use of acetic acid in the study of nuclear constituents is supported by its effect on the egg of Allolobophora. It unquestionably produces artefacts in both nucleolus and nucleoplasm.
Katharine Foot and E. C. Strobell 21?
the germinal vesicle takes part in forming the chromosomes of the first spindle. The evidence points rather to the conclusion that the apparent surplus of chromatin in this egg is due to its earlier artificial combination -with the achromatic substance causing a misconception as to the actual amount, and that all the chromatin, excepting that possibly contributed to the accessory nucleoli, is finally consigned to the chromosomes.
We have not attempted to analyze the reticulum by differential anilin staining, because the experimenting we have done Math anilins on later stages of the egg, has convinced us of the justice of the criticism of those investigators who question all results obtained by this method. Our aim is to ])lace in evidence only such phenomena as can be seen and photographed without the aid of any complicated method of staining, and in nearly all cases we control the evidence of the stained preparations by photographs of unstained sections, e. g.. Photos. 68 and 69, Plate IV, and forty other unstained sections showing nucleoli, centrosomes, archoplasm, etc.
With thin unstained sections much can be seen and photographed at a thousand diameters — tlie centriole and even individual microsomes can he clearlv registered hy photographs and such evidence as this method furnishes is at least relatively reliable. It may be an objection that this simple method throws out of court a number of so-called nuclear structures, for we are indelited to the anilin stains for several analytical subdivisions of the reticulum, e. g., Heidenhains' lanthanin or oxy chromatin granules which, according to Tellyesniczky. '02, are the same as Schwartz's paralinin and Pflitzner's parachromatin — the non-staining linin, and Eeinke's oedematin spheres, or cyanophilous granules. It may be justly asked, whether this is a question of indebtedness to the anilins or a score to settle.
Chromosomes. — The development of the 11 tetrads and their subsequent division in the first maturation spindle are so clearly demonstrated hy our new method descril:ied on p. 200 that the successive steps of the process can be illustrated l)y a few photographs " of these preparations (Plates YII, YIII and ix").
In the dried germinal vesicles of eggs from the distal end of the ovary and of the youngest eggs from the receptacida ovorum we have been unable to identify any differentiation of the nucleoplasm into the rela "We have more than two hundred preparations demonstrating these stages with equal clearness and many of these we have already photographed. In a future paper we shall reproduce some of them in connection with photographs of later stages demonstrated by the same method.
218 First Alaluratiuu SpiiulJo of Allolubopliora Fcotida
tivcly achromatic and chromatic segregation which appears hiter. Plioto. Ill, Plate yil, shows an early stage of the segregation of the diffused chromatin into a delicate thread or threads which later form the pronounced spireme of Photo. 113. At this early stage of the spireme the entire germinal vesicle is traversed hy a delicate thread so closely entwined that it gives the appearance of a network and it has heen impossible to determine whether this is composed of one continuous thread. Photo. Ill represents a typical distribution of the chromatin at this stage. "We have a large number of similar preparations and many photographs, l3ut lack of space prevents our reproducing more than one.
Photo. 112, Plate A^II, shows a very different segregation of the chromatin, the chromatic granules of the nucleoplasm are collecting directly into a coil-like structure without passing through the stage shown in Photo. 111. We have only one such preparation and we interpret it as abnormal, but ha\'e reproduced it because it shows so clearly that the chromatin is distributed throughout the entire germinal vesicle, and because that part of the nucleoplasm which is not 3'et differentiated into chromatin and achromatin gives a very faithful picture of the entire nucleoplasm of oocytes in an earlier stage of development. The granular nucleoplasm as shown on the right periphery of the germinal vesicle of Photo. 112 gradually segregates (in normal eggs) into an extremely delicate chromatic network, which is at first as indistinct as that shown at the left side of the germinal vesicle of Photo. 111.
Photo. 113, Plate VII, is a germinal vesicle showing a typical early stage of the spireme. A study of this photograph in the light of Photo. Ill suggests that the spireme of Photo. 113 has been formed by a contraction and thickening of the delicate thread or threads of Photo. Ill or by the fusing of parallel strands.
A study of Plioto. 11-i in the light of Photo. 113, Plate VII, suggests that each part of the double thread of Photo. 114 may be the single thread of Photo. 113, or, as we are inclined to think, that the single thread has increased in thickness by contraction and growth and has subsequently split. The longitudinal split of the spireme seen in Photos. 11-t and 115 persists throughout the prophase and can be clearly seen in many of the chromosomes at the metaphase (cf. Plates VIII and IX). "We interpret Photos. 114 and 115 as a later stage than Photo. 113 because the thread has commenced to break apart transversely to form the eleven bivalent chromosomes.
In Photo. 116, Plate VII, the entire spireme has divided into bivalent chromosomes with the exception of the two bivalent chromosomes which are close to the accessory nucleolus. These are still attached end to end.
Ivatliarine Foot and E. C. Strobell 21J) forming a part of the original coil including four univalent chromosomes or two bivalent chromosomes. The bivalent character is shown in the lower of the two chromosomes by a clear space in the center, and a similar clear space is shown in the l^ivalent chromosome just northeast of the accessor!/ nucleolus.
We have several intermediate stages between Photos. 115 and 116, Plate VII, where the chromosomes are in the form of long thread-like loops, but lack of space prevents our reproducing them. The bivalent character of the chromosomes is clearly shown in many of the photographs. The three rings in the upper part of Photo. 117, Plate VIII, show not only that each ring is composed of two univalent chromosomes attached end to end, but the longitudinal split of each is indicated, completing the transverse and longitudinal markings typical of the tetrad. We may say that the chromosomes of the prophase and metaphase are typical tetrads, for in every preparation in which- the eleven chromosomes are shown, one or more of them show beyond question both the longitudinal and transverse markings.
In Photo. 118, Plate VIII, at least five of the eleven chromosomes show the transverse constriction, though in all these chromosomes the longitudinal split is obscured. In Photo. 119 the tetrad character of at least five of the chromosomes is almost schematically shown, the large figure 8 shows not only the longitudinal split but a marked constriction in each loop indicating the point of contact of the two univalent chromosomes. The small chromosome southwest of the figure 8 shows with equal clearness its bivalent character and the longitudinal split, and the three bivalent chromosomes north of the figure 8 admit of only one interpretation. The fact that eleven bivalent chromosomes are typical of the prophases of the first maturation spindle of AUolohophora is demonstrated by the photographs of Plate VIII and the tetrad character of these chromosomes is clearly shown. A good deal of scepticism has recently been expressed as to the constancy of the number of the chromosomes in the first spindle, discrediting the great significance that has been attached to this point. We would therefore accentuate the fact that in every case where the chromosomes are so distributed as to admit of an accurate count, we have not found a single exception to the number eleven in the prophases and metaphase. Eods, rings and figures 8 are the most common forms, though there are examples of the cross-shaped chromosome which several investigators have demonstrated in other forms. In Allolobophora an interpretation of their origin appears to present no difficulties, they undoubtedly arise by a simple contraction of a bivalent chromosome, i. e., two rod-shaped univalent chromosomes
220 First Maturation Spindle of Aliolobophora Foetida
placed end to end. As they contract and are pressed together each splits open along the line of the longitudinal furrow, the ends are thus pressed out at right angles forming the two arms of the cross. As our preparations show the cross type of chromosome in all stages of its development, no other explanation of its origin for this egg seems possible. The beginning of the formation of a cross is seen in Photo. 124, Plate VIII, in contact with the asymmetrical figure 8, and northeast of it a cross in a further stage of development. Varying forms of the cross chromosomes are seen in Photos. 117, 120, 123, Plate VIII, and 116, Plate VII. The last photograph shows also the first stage of a cross formation in the bivalent small chromosome at the lower periphery of the germinal vesicle, and in Photo. 126, Plate IX, the method of forming a cross is almost schematically shown in the fourth chromosome from the left periphery of the photograph.
In the jDreparations reproduced on Plate IX the membrane of the germinal vesicle as well as the principal and accessory fiucIeoU have disappeared. The eleven bivalent chromosomes in all cases are present and in Photos 129 and 130 are symmetrically arranged in the equator of the spindle ready to divide. These preparations appear to us to demonstrate conclusively that the first division separates two univalent chromosomes, but we do not yet know that these two univalent chromosomes are two of the somatic chromosomes of the oogonia, so we cannot assert that the first division is a reducing division in Weismann's sense. We can only say that the prophases and metaphase of the first maturation spindle of AUolohopliora support the observations of Korschelt, Montgomery and others, who do claim that the first division is reducing. But in Alloloiophora several questions still remain unanswered. Does each bivalent chromosome represent two somatic chromosomes which are exactly similar in size and form, or does this exact similarity only indicate a foreshadowing of the first division ? Do the two represent the paternal and maternal inheritance as held by Montgomery, 'oi, Sutton, '02, and others, or does the longitudinal furrow indicate this double line of inheritance ? We must delay an attempt to answer these questions until we can determine whether the pairs of chromosomes, represented by the bivalent chromosomes of the prophase, are present in the oogonia as Montgomery and Sutton find them in certain insects, and whether tlie longitudinal furrow of the prophase can be explained as a foreshadowing of the second division.
The photographs of Plates VII and VIII demonstrate that the ring chromosomes are formed by the uniting of the free ends of two univalent chromosomes and the photographs of Plate IX show that such rings are divided at the metaphase at the points of contact of these two chromo
Katharine Foot and E. C. S.trobell 221
somes. In most cases this point of contact is expressed by a clear space or by a knob-like thickening. The clear space is shown in the three rings of Photo. 117, Plate VIII, and in one or more of the chromosomes in Photos. 116 to 130, Plates VII, VIII and IX. The knob-like thickening at the point of contact of two univalent cliromosomes is shown in one of the chromosomes of Photos. 116 and 130.
That the spindles must have some tenacity of form in the living egg is demonstrated by the characteristic spindle formation with the two polar spheres often remaining undisturbed by the process of pricking the membrane of the egg and allowing the cytoplasm to flow out upon the slide. An indication of the spindle form is shown in Photos. 125, 128, 129 and 130, Plate IX. The fact that the egg is dried so rapidly that the form of the spindle is not distorted argues that some confidence may be placed in the form of the chromosomes as well.
In the equator of the spindle of Photo. 125, Plate IX, a ring chromosome is seen showing a distinct longitudinal split and the clear transverse sj)ace which indicates one point of contact of the two univalent chromosomes which form the ring. This space is in the equator and unquestionably indicates one of the points of separation of this chromosome. The chromosome on the extreme left shows a like clear space, the other half of the ring, having already separated and contracted, resulting in one of the forms typical of the metaphase (the lower arm of this chromosome is in contact with the upper arm of a like chromosome). This form of division is seen in two of the chromosomes of Photo. 128, in at least five of the chromosomes of Photo. 129 and five of Photo. 130, Plate IX. Rings with a longitudinal furrow and characteristic indications at the points of contact of the univalent chromosomes of which they are formed are shown in Photo.- 126, Plate IX, and three similar rings dividing transversely are shown in Photo. 127, the one near the center of the photograph being especially instructive. These examples, with the ring of Photo. 129 and the two rings of Photo. 130, Plate IX, appear to dispel all doubt as to the manner in which the bivalent chromosome of Allolohophora is divided in the first maturation division. In each of these six photographs there are examples also of the simple transverse separation of the two rods attached end to end which represent the simplest form of these bivalent chromosomes. Many of them still show the longitudinal furrow which has persisted from the spireme stage and leave no doubt that this division is not along the lines of this longitudinal split.
^lany of the chromosomes demonstrated in the spindles of our Plate IX closely resemble those figured by Nelcrassoff, '03, in the first matur16
223 First Maturation Spindle of iMlolobophora Foetida
ation spindle of Cymbulia, Fig. 7, though he interprets their division as longitudinal.
This egg agrees with the observations of the many investigators who have demonstrated for both oocytes and spermatocytes a marked difference in the size of the chromosomes of the first spindle. In Crepidula, Conklin, '02, has shown this inequality to have reached the ratio of one to fifteen in volume. In Allolohophora the inequality in the size of the chromosomes is distinctly seen at the prophases and metaphase ; compare the two chromosomes in the same germinal vesicle of Photos. 51 and. 52, Plate III, and chromosomes in the germinal vesicle of Photo. 116, Plate VII, and those of Plate VIII. Compare the size of the chromosomes in the first i^pindle (metaphase) Photo. 33, Plate II, and. those of Plate IX.
It is more difficult, however, to demonstrate a persistent and individual form for each chromosome and in fixed and sectioned eggs we have found this quite impossible. For example, in a collection of thirty-four photographs showing every chromosome in four first spindles at the metaphase it was impossible to identify any one chromosome in the four spindles as the same individual. This is undoubtedly due in part to distortion of normal forms by fixation and as a rule the chromosomes are so closely massed in fixed material that their individuality is obscured (e. g.. Photos. 69 and 70, Plate IV, 85 to 89, Plate V). In dried germinal vesicles this massing of the chromosomes is avoided and individuals can be distinctly differentiated. Although the individuality of these chromosomes is not sufficienth^ pronounced to admit of a definite identification of the individual at each stage, a comparison of the chromosomes of the prophases of Plate VIII with those of the metaphase on Plate IX will demonstrate that a few of the individual chromosomes of the prophases can be identified in the metaphase with some accuracy, and this argues strongly for the individuality of all, and supports the theory which has been so frequently and ably defended by Boveri."
The prophases of the first spindle of Allolohophora as above demonstrated confirm A'^om Path's interpretation of the prophases of the first spindle of the spermatocytes of Gryllotalpha published in 1892. When
'^ After our paper had gone to press Baumgartner's interesting article appeared, giving " Some new Evidence for the Individuality of the Chromosomes," Bio. Bull., Vol. VIII, 1904. Our Photos. 116 to 130, Plates VII, VIII and IX demonstrate that Baumgartner's suggestive conclusions are not supported by the egg of Allolobophora. We find no constant form differences of the chromosomes, the simplest form of the bivalent chromosome is two rods attached end to end, and these present a variety of shapes, rings, figures 8, crosses, etc., without any regularity or constancy. The free ends of the
Katharine Foot and E. C. Strobell 223
the " Samenmuttenzelle " (spermatocytes 1st order of authors) has attained its growth the chromatin is distributed as a delicate " Maschenwerk" (cf. his Figs. 10 and 11 with our Photo. Ill, Plate VII). He next figures and describes the chromatin as a coil with a single longitudinal split (Fig. 12), this coil dividing transversely into half the number of somatic chromosomes, each of the bivalent segments representing two somatic chromosomes attached end to end, later their free ends uniting to form rings, these rings showing the same longitudinal split which he demonstrated in the coil. He is uncertain, however, whether this longitudinal split foreshadows the first or second division. He says : " Es kann folglich die eine der beiden Trennungen der Chromosomen auf diese vorseitige Spaltung des Chromatinfadens zuriickgefiihrt werden; ob dies nun aber die erste oder die zweite Theilung ist, kann nach den Priiparaten nicht mit Sicherheit entschieden werden, ich mochte eher an die zweite Theilung denken," p. 113.
Montgomery's, 'oi, '04, interpretation of the prophases studied in a variety of forms, is supported by AUolohoplwra in the longitudinal split of the coil (cf. Montgomery's '04, Figs. 10 and 11 with our Photos. 114 and 115, Plate VII), and the separation of the univalent chromosomes at the first division, but this egg does not support Montgomery in certain points in which his observations differ from those of Vom Rath, Riickert and Hacker. These points are clearly stated by Montgomery, '04: " Eiickert, '94a, and Hacker and others after him, concluded that there was a continuous chromatin spireme preceding the first maturation mitosis, and that the apparent reduction in number of the chromosomes is effected by this cliromatin spireme segmenting into half the normal number of chromosomes. I showed for Peripatus, '00, on the contrary, that a continuous linin spireme is present at this stage but not a continuous chromatin spireme, and that the bivalent chromosomes are produced by a later conjugation without the formation of a continuous chromatin loop. According to Riickert it is a case of chromosomes already closely connected remaining so; according to me, of chromosomes not in contact at first, becoming so secondarily. Hence I spoke of this act as the conjugation of the chromosomes, and argued that this is the important
bivalent chromosomes show a tendency to unite into a ring and in some cases nearly all the eleven chromosomes are rings (Photo. 122), and sometimes not a single ring is formed, Photos. 116 and 118. This by no means disproves Baumgartner's conclusions, for the variety of shapes of the chromosomes of AllolohopTiora may be due to mechanical disturbance of the living form incident to the technique. This point can be determined only by the study of living chromosomes.
224 First "Maturation Spiiullc of All()l()!)0])liora Fretida
criterion of the synapsis stage." The photographs of our Plates VII and VIII demonstrate that in AUoIohophora "it is a case of chromosomes already closely connected remaining so."
Many of our photographs confirm A. and K. E. Schreiner's, '04, observations on the spermatocytes of Myxinc r/lutinosa and Spinax niger. The delicate thread-like reticulum in the early prophase (cf. Fig. 2 with our Photo. Ill), the coarse spireme of the later stage (cf. their Figs. 3, 5 and 23 with our Photos. 114 and 115, Plate VII), and finally the form of the bivalent chromosomes. The rings, figures 8, etc., of Schreiner's Fig. 15 are reproduced in Allololiopliora, though in their mode of formation and subsequent division there are fundamental differences. They interpret the first furrow of the spireme as due to a union 'of two of the delicate threads of the earlier stage, and at a later stage they identify a second longitudinal split of the spireme, these two longitudinal divisions indi'cating'the method of separation of the chromosomes for the first and second divisions. The individuals of each bivalent chromosome are paired longitudinally in the spireme, whereas in Allolohopliora they are placed end to end, thus though the rings, figures 8, etc., of Schreiner's Fig. 15 and those of Allolohopliora are formed alike by the uniting of the ends of two univalent chromosomes, they have attained this final .arrangement by an entirely different method. In both forms, therefore, the first division separates univalent chromosomes, though in one case the division is longitudinal and in the other transverse.
This transverse division of the chromosomes supports Lillie's, '01, observations on Unio. He says, " The first division is certainly at right angles to the long axis of the chromosomes, as these lie in the equatorial plate," p. 236.
The spireme demonstrated in our photographs of Plate VII and the " heterotypic " chromosomes of Plate IX confirm Flemming's obser•vations on the spermatocytes of Salamandra maculosa published in 1887. "The "heterotypic" chromosomes of his Figs. 22, 23 and 25 are accurately Teproduced in several of our photographs of Plate IX. Since the ring ■chromosome was demonstrated by Flemming many investigators have identified them in a variety of forms. The ring chromosomes of our photographs of Plates VIII and IX are similar to those demonstrated by Henking," '91, in Pyrrliocoris ; Moore, '95, in Elasmobranchs; Bolles Lee, '97, in Helix; von Klinckqwstrom, '97, in Prostheceraeus, de Sinety, '01, in Orthoptera, Schockaert, '04, in Thysanozoon and Montgomery, '04, in
^^ Henking interprets the first division as a reducing division and the second as an equation division.
Katharine Foot and E. C. "Strobell 225
Plethodon. McClimg, 'oo-'o2, lias shown rings, figures 8 and crosses in certain insects clcarl}' demonstrated by excellent photographs. Helen Dean King, 'oi, has demonstrated the ring in the egg of Bufo, and her interpretation that the knob-like thickenings represent " the place of union of the two chromosomes that fused to form the ring " is confirmed by the photographs of our Plates VII and VIII; in Allolohophora, however, the rings do not divide longitudinally in the first division as in Bufo.
Many forms of the chromosomes in Allolohopliora are similar to those demonstrated by Korschelt, '95, in Opliryotrocha and his interpretation of the first division separating two univalent chromosomes is confirmed by the photographs of our Plates VII, VIII and IX. Further details in wdiich Korschelt's observations are supported by this egg are stated under the heading " Comparisons with other Annelids."
ArcJio plasm.- — In earlier papers we have used Boveri's, '88, term archoplasm for that substance in the cytoplasm which in the youngest oocytes is massed in different shapes close to the germinal vesicle (yolk nucleus of authors). As the egg grows this substance increases in amount, becomes distributed throughout the cj^toplasm; after fertilization much of it gradually segregating to the periphery, and finally a large part of it contributing to the formation of the polar rings. We use the term archoplasm because at definite phases of the development of the egg the substance appears to contribute to the formation of asters and spindles and may thus be the homologue of Boveri's archoplasm. • Progressive steps in the development of the substance from yolk nucleus to polar rings were illustrated b}' a series of photographs (Foot and Strobell, '01), but in the present paper we have reproduced only three sections of the earlier stages, merely to illustrate our interpretation. At the upper periphery of Photo. 12 about half of a very small oocyte is shown, with a mass of archoplasm (yolk nucleus) at the opposite poles of its nucleus. . The next stage represented in this paper is shown in Photo. 7G, Plate IV, the archoplasm being somewhat removed from the nuclear membrane. A later stage is seen in Photo. 78, Plate IV, in which the substance is distributed throughout the cytoplasm, and Photo. 12 shows a like distribution in an older oocyte. In recent investigations of this polar-ring substance w^e have attempted no analysis by complicated methods of staining, studying it only in the light of comparative fixation and aiming thus to demonstrate its presence in eggs in which, after some fixatives, its identity is questionable.
It is interesting to compare the effects of fixation on the two constituents of the cytoplasm, chromatic arclioplasm and relatively achro
226 First IMaturation Spindle of Allolobopliora Foetida
matic cytoplasm, with the etl'ects of fixation on the two nuclear constituents, chromatin and achromatic nucleoplasm, for in both cases the reaction to fixation is strikingly alike. Such a crude comparison is instructive only to illustrate the fact that both chromatin and archoplasm can be identified after some fixatives and obliterated after others, yet the specific character of chromatin is universally admitted, whereas the specific character of archoplasm has been very generally doubted. We do not mean to imply that the two substances, archoplasm and achromatic cytoplasm, are the sole constituents of the cytoplasm, any more than the chromatin and achromatic nucleoplasm may be the sole constituents of the nucleus. Archoplasm and achromatic cytoplasm are as much at the mercy of the fixatives as are the chromatin and achromatic nucleoplasm, and, like them, can be fused together into a network or into masses in which the constituents are indistinguishable, or they may be so separated that the two are readily differentiated. Such a differentiation is seen in the unstained sections of Photos. 68 and 69, Plate IV, the chromatic archoplasm and relatively achromatic cytoplasm being segregated into quite definite areas. We do not claim that such pronounced cases of segregations more nearly approximate the living condition, but they may be instructive as an aid to demonstrating the individuality and continuity of the substances during these stages, and the same may be said of some forms of segregated chromatin shown in many of our photographs of sections. The achromatic cytoplasm of Photos. 10, Plate I, 68 and 69, Plate IV, like the achromatic nucleoplasm, is a relatively homogeneous substance, but it becomes granular and chromatic when combined with the archoplasm (Photo. 13, Plate I, just as does the achromatic nucleoplasm when combined with chromatin (cf. the nucleoplasm of Photo. 34, Plate II, with that of the germinal vesicles of Plates II, III, IV). Aggregations of archoplasm like the three shown in Photo. 13 are distributed throughout the cytoplasm of the entire egg (cf. Foot and Strobell. '98, Photo. -9). Such aggregations are typical of chromo-acetic preparations and in the light of our recent study of the germinal vesicle we are convinced that the entire cytoplasm of such preparations represents an artificial combination of archoplasm and achromatic c3^toplasm comparable to the fusing of the chromatin and achromatic nucleoplasm in the germinal vesicles of the same preparations (Photo. 34), and they support the observations of the investigators who question the specific nature of archoplasm. Such an interpretation would be supported also by Photo. 100, Plate VI, but a comparison of these two photographs (13 and 100) with 68 and 69, Plate IV, suggests that the individuality of the archoplasm, so clearly shown in the last two photographs, is only obscui'cd
Katliarine Foot and E. C Stroboll 227
in Photos. 13 and 100. Wc believe the ehroniatic granular substance of the prophase (Photos'. 68 and 69) is the same as the chromatic granular substance of the metaphase (Photo. 99, Plate VI). These eggs were killed in the same fixative, platino-osmic, and the substance can be recognized at the two stages. In Photo. 100 the substance has a very different distribution from that of Photo. 99, Plate VI, though the two eggs are at exactly the same stage of development, i. e., metaphase of the first spindle. In the chromo-acetic preparation (Photo. 100) the homogeneous achromatic cytoplasm is in the form of pronounced rays, combined in such a way with the archoplasm that the latter may be interpreted as cyto-microsomes. After some fixatives it certainly does assume the form of cyto-microsomes and in these cases its identification as a specific substance is possible only where it is accumulated into dense masses. Its interpretation as a specific substance or as an integral part of the cytoplasm depends upon its special manifestation after a given fixative and suggests that the opposing interpretations are largely a question of terms. In this egg we claim its individuality only on the ground that we think we can trace the substance with unbroken continuity from its earliest aggregation as yolk nucleus in the youngest oocytes to the cleavage stages — a large part of it contributing to the formation of the polar rings. Aggregations of archoplasm not alone in chromo-acetic preparations, but in corrosive sublimate and many others are readily differentiated by double staining (Foot, '96), but this method obscures its presence when it is most evenly distributed throughout the egg, and for this reason study of comparative fixation has seemed the more profitable method to follow (Foot and Strobell, '00) . When the oocyte first order has reached its maximum growth it is especially difficult to differentiate the archoplasm. Its presence at this stage is demonstrated in Photos. 68 and 69, Plate IV, and Photo. 10, Plate I, shows an interesting segregation of the substance in the form of a " polar ring which is not normal^ due until the pronuclear stage. This is a section of an oocyte with the germinal vesicle intact and the chromosomes not yet formed, a stage earlier than that shown in Photos. 68 and 69. There is a similar aggregation of archoplasm at the opposite pole of this egg and these two polar aggregations present a striking resemblance to many polar rings of the pronuclear stages which are not invariably in the form of a ring. This precocious polar segregation of the substance in Photo. 10 appears to us to demonstrate tlie presence of this definite substance in the egg during these early stages and the granular appearance of the archoplasm in this pliotograph is typical of all fixed material. The chromatic centers of asters fail to show this granular effect (Photos. 84,
228 First Maturation Spindle of Allolobophora Foetida
86, 91, 93, Plate V, 99 to 110, Plate VI), but we do not think this necessarily means that these centers are devoid of archoplasin ; it may indicate rather a definite chemical combination with the achromatic cytoplasm that causes a different morphological reaction to fixation (Foot, '96). An obvious contribution of archoplasm to the spheres is largely dependent on fixation, and in some cases it is aggregated into granular masses or heavy rays around the mark-zone (Foot and Strobell, .'00), and again the mark-zone itself is granular and stains intensely.
Differentiation of a special chromatic substance in the cytoplasm of young oocytes or spermatocytes is very common, but more rarely is this substance traced to the later stages of development. Among recent papers Voinov, '03, has traced a substance to the first spindle in Cybister, and finally to the Kebenkern. He has designated it as " zone interne " as distinguished from his " zone externe " (Figs. 29 and 30), and a comparison of his figures with our photographs leads to the impression that the archoplasm of AUolodopliora is synonymous with his " Mitochondria " (Benda's) and "zone interne" combined (see his Figs. 35 and 39).
Data as to the specific nature of polar-ring substance have been presented by Wilson in his interesting paper on Dentalium, '04. He identifies an upper and lower polar area in the oocyte and of these he says: , "I believe it is probable that at least the lower protoplasmic area and probably also the upper disc are in a general way comparable to, if not identical with, the polar rings observed in the eggs of certain leeches and Oligochcetes." Of the lower polar area he says: "It is evident that material from the interior of the egg must flow into the lobe as it forms,'^ and of the upper polar area he adds : " It is here again evident that an extensive flow of this material must take place from the interior of the Qgg" (pp. 12-15). These facts have a special bearing on our interpretation that the polar ring substance is distributed throughout the egg and later aggregates at the poles. (Foot and Strobell, '98-) Wilson interprets both areas as " specific cytoplasmic material."
In this connection Wheeler's w^ork on Myzostoma, '97, is of special interest. He interprets certain phenomena at the upper pole of the egg as homologous to the polar rings of Annelids and he identifies in the oocyte (Fig. 1) a denser area of protoplasm which strikingly resembles the yolk nucleus of AUolohophora and this he traces to the yolk-lobe (opposite pole), though he does not interpret the substance as yolknucleus, nor the yolk-lobe as homologous to a polar ring of Annelids. Conklin, however, in 1897, identifies at the vegetal pole of the egg of Crepidula a mass of hyaline substance which he homologizes to the yolk-lobe described by Mead in ClKBtopterus and to the polar rings of
Kaiharine Foot and E. C. Strobell 229
Annelids. He says : " I am convinced that this peculiar body is homologous with the problematical lobe which is described by Mead, '95, in the egg of Chcctoptcrus and further it is probably identical with the pohir rings observed by Wliitman, '78, in Clepsine and since then by various authors in different Annelids."
Comparisons with Other Annelids.
In the oogenesis of Annelids there has been very little work done on the prophases of the first maturation spindle.
Among the Lvmhricidae we have not found any record of observations on these stages, but in the spermatogenesis of Lnmhricus terrestris Calkins, '95, has studied the prophases of the first division and the two species, AUolohophora and Lumhricus, are in accord in showing a spireme with a longitudinal furrow. In Lumhricus, however, the spireme divides transversely into the full number of somatic chromosomes, and there is, therefore, no numerical reduction of the chromosomes by two univalent chromosomes remaining attached end to end as in AUolohophora.
In the first spindle of Lumhricus there are sixteen tetrads, the spermatocytes second order receiving each sixteen double chromosomes. Calkins adds : " Whether this is a reducing division in Weismann's sense cannot be ascertained."
Vejdovsky's and Mrazek's recent valuable work, '03, on Rhynchelmis is confined to later stages, the material being unfavorable for the study of the prophases of the first maturation spindle. Of these stages they say : " Das Studium der ersten Vorgange der Eireif ung ist schon technisch sehr zeitraubend, wenn man auf den endlosen Schnittserien durch die einige Zentimeter langen von Eiern prall angefiillten vorderen Abschnitte des Wurmleibes stets nur entweder noch ruhenden Kernen oder den bereits fertigen Eeifungsspindeln begegnet" (pp. 454 and 455). They have, however, supplemented their work on Rhynchelmis by a study of the prophases of the first spindle in Tuhifex, Limnodrilus and Ilyodriliis, but their results are demonstrated by a single text figure showing a germinal vesicle with tetrads. In explanation of this figure they say : " Den ganzen Vorgang der Chromosomenbildung konnten wir nicht verfolgen. Erst in spateren Stadien fanden wir die in Textfigur 3 abgebildeten Formen der Chromosomen. Es sind dies Gebilde, die wie aus zwei dicht an einander gelegten sichel- oder biskuitformgen Teilen zusammengesetzt erscheinen. Ein Vergleich mit den an anderen Objekten gewonnenen Eesultaten fiihrt zu dem Ergebnisse, das wir hier langsgespaltene doppelwertige Elemente vor uns haben, die den typischen
230 First Maturation Spindle of Allolobophora Foetida
Vierergruppcn entsprechcn. Wie die Abbildung zeigt, kann die Form der einzelnen Griippen etwas variieren, dock muss ausdriicklich bemerkt werden, dass wir JJingbildimgen niemals beobachten konnten. Dagegen sind kreuz- oder x-formige Fignren die haufigsten."
In Text Figs, -i and 7 they show 37 different forms of the chromosomes of the first maturation spindle of Rliyricliehnis. In our Photo. 72, Plate IV, there is an exact duplicate of one of the chromosomes in their Text Fig. 4, and a comparison of their other figures with our photographs of the first spindle of Allolobophora (Plate IX and our Text Fig. 4 of an earlier paper, '98), show a suggestive similarity in form. Vejdovsky and Mrazek state, and their Text Fig. 5 demonstrates, that only the central part of the first maturation spindle of Ilyodrilus is of nuclear origin, but in Allolohophora a much larger proportion of the spindle is derived from the achromatic nucleoplasm of the germinal vesicle (see Photos. 84 to 89, Plate V). On this point Allolobophora is more in accord with Gathy's, '00, observations on Tubifex, though the membrane of the germinal vesicle persists longer in Tubifex than in Allolobophora. Gathy's Fig. 11 shows the first spindle nearly at the metaphase and yet the membrane of the germinal vesicle is almost intact, whereas in Allolobophora the nuclear membrane entirely disappears before the spindle reaches the metaphase. Our Photos. 84 to 89, Plate V, show part of the membrane of the germinal vesicle persisting until both centrioles and asters are present at opposite poles, though not developed to the stage shown in Gathy's Figs. 10 or 11; these photographs indicate, however, that the achromatic nucleoplasm of the germinal vesicle of Allolobophora, like Tubifex, contributes to a large part of the first maturation spindle. Allolobophora further supports Gathy's observations as to the independent origin of the two centrioles, their first appearance close to the nuclear membrane and the indication that the spindle is formed under their influence. Gathy omits other important details in the formation of the spindle and his Figs. 8, 9 and 10 demonstrate that he has not observed the successive steps of the development of the chromatin of the germinal vesicle into the chromosomes.
Among the Annelids these stages have been most thoroughly investigated by Korschelt in Ophryolrocha. '95, and Allolobophora corroborates almost every detail of the process Korschelt describes. In both Oligoclurtes the chromatin forms a skein, though in Ophrijotrocha the longitudinal furrow does not appear until after the chromosomes are formed. The skein divides transversely into chromosomes, in Opliryotroclia these being univalent, whereas in Allolobophora they are bivalent, as a rule remaining bivalent until separated at the anaphase of the first spindle.
Katharine Foot and E. C. Strobell 231
In both Oligorlia'tes the chromosomes have a distinct longitudinal furrow, which has persisted in AUolohophora from the skein stage, and in both forms the first division separates two univalent chromosomes. In these two Annelids the achromatic nucleoplasm contributes to the formation of the spindle fibers, the fibers forming within the germinal vesicle while its membrane is partly intact^ and the centriole in both cases is first seen outside the germinal vesicle close to its membrane, though in Ophryotroclia the two arise by division of one, while in AUolohophora they are first seen at opposite poles of the vesicle.
Thalassema. — Griffin's interesting paper on the maturation and fertilization of the egg of Thalassema, '99, gives a clear demonstration of the prophases of the first maturation spindle. These are reproduced in his Figs. 1 to 12, but Griffin demonstrates no spireme in the germinal vesicle, and he neither figures nor describes stages answering to the stages shown in our Photos. Ill to 115, Plate VII, and in Korschelt's, '95, Figs. 67 to 74. He figures a spireme only in the nuclei of " minute ova, the size of these nuclei in relation to the germinal vesicles of later stages showing them to be the young nuclei emerging from the telophase of the last oogonial division, and the spireme of these nuclei is not comparable to the spireme demonstrated in our photographs of Plate VII. They can be compared only to similar minute cells in the ovary of AUolohophora. stages with which we are not concerned in the present paper. In the text Griffin describes the spireme of the nuclei of these minute cells as showing an occasional longitudinal split and dividing transversely into bivalent chromosomes at the heginning of the growth, period (Fig. 2), these chromosomes persisting as double rods throughout the entire growth period" (p. 605). In AUolohophora the chromosomes do not persist through the growth period nor can any indication of the aggregation of the diffused chromatin into the spireme of Photos. Ill to 115 be demonstrated until some time after the germinal vesicle has attained its maximum size (see p. 217 for details). The two Annelids agree, however, as to the form of the final tetrads. Griffin's Text Figs. 1 and 2 show chromosomes in the form of rings, figures 8, crosses, etc., which are strikingly like those in many of our photographs, though their origin is apparently very different. In Thalassema the spireme divides transversely into half the number of somatic segments, these bivalent chromosomes differing, however, from AUolohophora in the important point that their bivalent character is expressed by a longitudinal division of each, instead of two univalent chromosomes being attached end to end. as in AUolohophora. Thus the rings, figures 8, etc., which are common for the two Annelids have a different origin, necessitating a different
232 First Maturation Spindle of Allolobopliora Foetida
interpretation for the first division, in Thalai^sema the first division being longitudinal (giving to each cell one-half of every univalent chromosome) , and in Allolobopliora transverse (giving to each cell entire univalent chromosomes, each receiving one-half the somatic number). Griffin has clearly stated his results in the following summary :
"1. By longitudinal fission and transverse segmentation of the spireme thread, there arise 12 (reduced number) ellipse-shaped chromatin masses.
" 2. These persist throughout the growth period of the egg.
" 3. During prophase they concentrate into crosses, the arms of which are tight loops.
" 4. In the first polar division these are drawn out again into ellipses which divide to form daughter- Y^s (equation division).
" 5. The V's break apart at the angle in the second polar division (reducing division)/^ p. 612.
The persistence of the chromosomes throughout the entire growth period, during the time that the nuclear reticulum is gradually developing, led Griffin to the conclusion that " its development is independent of the chromosomes which are passive during its growth" (p. 604), and Griffin's conclusions as to the independence of these two substances are supported by our observations on Allolohophora. The two Annelids are further in accord as to the first appearance of the maturation centrioles. In both types they are first seen as minute asters close to the germinal vesicle, though in Thalassema they are closer to each other than we have yet found them in Allolobopliora. This independence of the centrioles accords with Mead's observation on Chcetopterus, '98 (cf. our Photos. 81 and 82, Plate V, with Mead's Figs. 8 and 9). The two extremely small centrioles of the above-mentioned photographs show a more marked independence of origin than those figured by Mead, for they are at opposite poles of the germinal vesicle, while closer to its membrane and at an earlier stage of development than those figured for Chcetopterus. These primary asters of Chcetopterus " arise at some distance from the wall of the germinal vesicle," and Mead adds : " I am not prepared to say at present v/hether the primary asters are formed by the further growth and specialization of two of the secondary asters or by the union and coalescence of several." These secondary multiple asters which Mead has demonstrated in his Fig. 7, he has shown to be normal in Chatopterus, having watched the phenomena in living eggs, which continued to develop after the multiple asters had disappeared. In Allolobopliora we have found only one egg showing structures that could be interpreted as multiple asters, but the egg was unquestionably pathological, the germinal
Katharine Foot and E. C. Strobell 233
vesicle had brolcen down and its contents scattered tliroughout the cytoplasm. These structures in AUolohophora resemble some of the asters in Cerebratitlus which Kostanecki interj^rets as expressions of a pathological condition. They show, however, no evidence that they have originated by division of the normal aster as Kostanecki, '02, interprets those of Cerehraiulus, they indicate rather that their irregular dense centers are small aggregations of dispersed nuclear substance, around which cytoplasmic rays focus.
Mead gives no account of the development of the nine chromosomes* which he finds in the first maturation spindle. These stages are omitted also in Wheeler's work on Myzostoma, '97, where he first figures the chromosomes as 12 tetrads suspended in the chromatic network of the germinal vesicle. These are composed of two rods swollen at their ends, and of these Wheeler says : " I have not studied the origin of the double rods in the germinal vesicle so that I am unfortunately unable to pass an opinion on the nature of the division in the fii'st spindle. In the case of the second spindle, however, I feel confident that there is a longitudinal splitting of each of the single chromatin rods remaining in the egg after the formation of the first polar body" (p. 51). AUolohophora supports Wheeler's observations as to the occasional persistence of part of the membrane of the germinal vesicle until the spindle is formed (cf. Photos. 84 to 87, Plate Y, wdth Wheeler's Fig. 63). In Myzostoma the two centrioles are first seen near the membrane of the germinal vesicle and in close relation to each other, being " connected by a delicate achromatic bridge." Wheeler's Figs. 3 to 5 demonstrate the gradual separation of these centrioles to form the poles of the first spindle.
December 1, 190-1.
PAPERS REFERRED TO.
AxcEL, P., '02. — Histogenese et structure de la glande hermaphrodite d'Helix
pomatia (Linn.) Arch, de biologie, Tome XIX. Blackmax, M. W., '03. — The Spermatogenesis of the Myriopods. On the Chromatin in the Spermatocytes of Scolopendra heros. Bio. Bull., Vol. V.,
No. IV. BovERi, Th., '88. — Zellen-Studien. Jena. ■ 02. — Ueber mehrpolige Mitosen als Mittel zur Analyse des Zellkerns.
Vehr. d. phys. Med. Ges. Wixrzburg., N. F., Bd. XXXV. Bryce, Thos. H., '01. — Maturation of the Ovum in Echinus. Quart. Journ.
Mic. Sci., Vol. XLVI. Calkins, Gary N., '95. — The Spermatogenesis of Lutabricus. Jour.
Morph., XI. CoE, Wesley, R., 'gg. — The Maturation and Fertilization of the Egg of Cere bratulus. Zool. Jahrb., Bd. XII.
234 First Maturation Spindle of Allolobophora Fcetida
CoxKLiN, E. G., '97. — The Embryology of Crepidula. Journ. Morph., Vol. XIII,
No. 1. '02. — Karyokinesis and Cytokinesis. Journ. Acad. Nat. ScL, Phila.,
Vol. XII. Flemming, W., '87. — Neue Beitrage zur Kenntniss der Zelle. Arch. f. mik.
Anat., Bd. XXIX. Foot, Katharine, '96. — Yolk nucleus and Polar rings. Journ. Morph.,
Vol. XII.
'97. — The origin of the Cleavage Centrosomes. Journ. Morph., Vol. XII.
'98. — The Cocoons and Eggs of Allolobophora fcetida. Journ. Morph.,
Vol. XIV. Foot & Strobell, '98. — Further Notes on the Egg of Allolobophora foetida. Zoological Bulletin, Vol. IT, No. 3.
'00 and '01. — Photographs of the Egg of Allolobophora fcetida, I and II.
Journ. Morph., Vols. XVI and XVII.
'02. — Further Notes on the Cocoons of Allolobophora foetida. Bio. Bull.,
Vol. III.
Gathy, E.. '00. — Contributions a I'etude du developpement de I'oeuf et de la fecondation chez les Annelides. La Cellule, T. XVII.
Goldschmidt, R., '02. — Untersuchungen iiber die Eireifung, Befruchtung und Zelltheilung bei Polystomum integerrimum Rud. Zeit. f. wiss. Zool., Bd. LXXI.
Gbiffin, Bk. B., '95. — The History of the Achromatic Structures in the Maturation and Fertilization of Thalassema. Trans. N. Y. Acad. Sci.
'99. — Studies on the Maturation, Fertilization and Cleavage of Thal assema and Zirphgea. Jour. Morph., Vol. XV. Habtmann, Max., '02, — Ovarialei und Eireifung von Asterias glacialis. Zool.
Jahrb., Abt. f. Anat., Bd. XV. Henkixg, H., 'gi. — Ueber Spermatogenese und deren Beziehung zur Eient wicklung bei Pyrrhocoris apterus. Zeit. f. wissen. Zool., Bd. LI. King, Helen D., '01. — The Maturation and Fertilization of the Egg of Bufo
lentiginosus. Journ. Morph., Vol. XVII. Klinckowstrom, a. von, '97. — Beitrage zur Kenntniss der Eireifung und Befruchtung bei Prosthecerffius vittatus. Arch. f. mik. Anat., Bd. XLVIII. Korschelt, E., '95. — Ueber Kernteilung, Eireifung und Befruchtung bei Ophry otrocha puerilis. Zeit. f. wiss. Zool., Bd. LX. Kostanecki, K. v., '02. — Ueber abnorme Richtungskorpermitosen in befruchte ten Eiern von Cerebratulus marginatus. Abhandl. u. Bull. Akad.
Wiss., Krakau. Lebeun, H., '01. — La vesicule germinative et les globules polaires chez les
Anoures. La Cellule. T. XIX.
'02. — La vesicule germinative et les globules polaires chez les Batra ciens. La Cellule, T. XX. Lee, a. Bolles, '97. — Les cineses spermatogenetiques chez 1' Helix pomatia.
La Cellule, T. XII. Lillie, Frank R., '01. — The organization of the Egg of LTnio, based on a study
of its Maturation, Fertilization, and Cleavage. Journ. Morph., Vol.
XVII. No. 2.
Katharine Foot and E. C. Strobell 235
LuBOSH, WiLiiELJi, '02. — Ueber die Nucleolar-substanz des reifenden Tritoneneies nebst Betrachtungen iiber das Wesen der Eireifung. Jen. Zeit. f. Naturwissenscbaft, Bd. XXXVI.
Marshall and Hurst, '88. — Practical Zoology. Smitb, Elder & Co., London.
McCluxg, M. E., '00. — The Spermatocyte Divisions of the Acrididse. Bull. Uni. Kansas, Vol. 1, No. 2.
'02. — The Spermatocyte Divisions of the Locustidae. Kansas Uni. Sci.
Bull., Vol. I, No. 8. Mead, A. D., '98. — The Origin and Behavior of the Centrosomes in the Annelid
Egg. Journ. Morph., Vol. XIV, No. 2. Meves, Fr., '02. — Ueber die Frage, ob die Centrosomen Boveri's als allgemeine
und dauernde Zellorgane aufzufassen sind. Verhand. Anat. Gesell.,
Bd. XXI. Montgomery, Thos. H., Jr., '98. — Comparative Cytological Studies with especial
regard to the Morphology of the Nucleolus. Journ. Morph., Vol. XV,
No. 2. Montgomery, T. H., '01. — A Study of the Chromosomes of the Germ Cells of
the Metazoa. Trans. Amer. Phil. Soc, Vol. XX.
'04. — Some Observations and Considerations upon the Maturation Phe nomena of the Germ Cells. Bio. Bull., Vol. VI, No. 3. '04. — Prof. Valentin Haecker's Critical Review on Bastardization and
Formation of the Sex Cells. Zool. Anz., Bd. XXVII, No. 20, 21. Moore, J. E. S., '95. — On the Structural Changes in the Reproductive Cells
during the Spermatogenesis of Elasmobranchs. Quart. Journ. Micr.
Sci., N. S. 38. Nekkassoff, a., '03. — Untersuchungen iiber die Reifung und Befruchtung des
Eies von Cymbulia Peronii. Anat. Anz., Bd. XXIV. Schockaert, Rufits', '04. — La Fecondation et la Segmentation chez le Thysano zoon broschi. La Cellule, t. XXII. Scheeiner, a. and K. E., '04. — Die Reifungsteilungen bei den Wirbeltieren.
Ein Beitrage zur Frage nach der Chromatinreduktion. Anat. Anz.,
Bd. XXIV, No. 22. i)E SiNETY, '01. — Recherches sur la biologie et I'anatomie des Phasmes. La
Cellule, t. XL Stephax, p., '02. — Sur quelques points relatifs a revolution de la vesicule
germinative des Teleosteens. Arch, d'anat. Microscopique., T. V. SuTTOx, Walter S., '02. — On the Morphology of the Chromosome Group in
Brachystola Magna. Bio. Bull., Vol. IV. Tellyesxiczky, K., '02. — Zur Kritik der Kernstrukturen. Arch. f. mik. Anat.
u. Entw., Bd. LX. Vejdovsky, Fr., '88-'92. — Entwicklungsgeschichtliche Untersuchungen. Prag. Vejdovsky, Fr., und Mrazek, '03. — Umbildung des Cytoplasma wahrend der
Befruchtung und Zellteilung. Nach den Untersuchungen am Rhynchel mis-Eie. Arch. f. mik. Anat., Bd. LXII. VoiNOV, D. M., '03. — La spermatogenese d'et4 chez le Cybister Roeselii. Arch.
Zool. exper. et generale, Vol. I. VoM Rath, O., '92. — Zur Kenntniss der Spermatogenese von Gryllotalpha vulgaris Latr. Arch. f. mik. Anat., Bd. XL.
236 First Maturation Spindle of AUolobophora Foetida
Wheeler, William Morton, '97. — The Maturation, Fecondation and Early Cleavage of Myzostoma Glabrum Leuckart. Arch, de Biol., T. XV.
Wilson, E. B., 'ge-'oo. — The Cell in Development and Inheritance.
'04. — The Germ-regions in the Egg of Dentalium. The Journ. Exper.
Zool., Vol. I.
EXPLANATION OF PLATES.
All the photographs are of the egg of AUolobophora foetida and were taken by the method described in Zeit. f. wiss. mik., Bd. XVIII, 1901, "A new method of focusing in photo-micrography," Foot and Strobell.
The Zeiss apo. 2 mm. immers. lens 140 apr. and compensating ocular 4 were used, and for the one thousand magnification a camera draw of 25% inches.
Many of the photographs were taken on the Seed No. 27 and the Agfa Isolar plates. With these rapid plates an exposure of only one to three minutes was required even on cloudy days. In the photographs of Plates VII, VIII and IX the wider area of accurate focus demanded by the subjects made it necessary to close the substage diaphragm to a point requiring doubling the time of exposure.
Only a small part of each section is reproduced, except in photos. 68 and 69.
The reproductions of Plates I, IV and VI are by the half-tone process, and Plates II, III, V, VII, VIII and IX are by the Rotograph process.
PLATE I.
The oocytes shown in Photos. 1 to 11 inclusive were fixed in platino-osmic (Hermann's fiuid without acetic acid) and stained with iron haematoxylin followed by dilute Bismarck brown. All the sections are 2i/^^.
Photo. 1. X 1000. First of four consecutive sections of a germinal vesicle of an oocyte first order from a receptaculum ovorum, showing chromatic filaments stained black, and faintly stained nucleoplasm.
Photo. 2. x 1000. Next section to above.
Photo. 3. x 1000. Next section to Photo. 2 showing an accessory nucleolus stained black like the chromatic filaments. This is the only accessory nucleolus in this germinal vesicle.
Photo. 4. X 1000. Next section to above showing the principal nucleolus which stained yellow by the Bismarck brown. This nucleolus is also present in the two following sections.
Photo. 5. X 1000. Section of a germinal vesicle of an oocyte first order from the receptaculum ovorum, showing black chromatic filaments, and large yellow nucleolus with small black granules (these granules are lost in some of the reproductions). This section was first photographed unstained and the granules in the nucleolus were as black and sharply differentiated as in the stained preparation.
Photo. 6. X 1000. First of four serial sections of a germinal vesicle of an oocyte first order from receptaculum ovorum showing black chromatic filaments and one accessory nucleolus, also stained black.
Photo. 7. x 1000. Second section from above showing the principal nucleolus. This nucleolus stained brownish yellow and is present in the two following sections.
Katliarine Foot and E. C". 8ti-obcll 23 ^
Photo. 8. x 1000. Next section to Photo. 7 showing the same large nucleolus and a second accessory nucleolus stained Ijlack. at the upper left hand periphery of the germinal vesicle.
Photo. 9. x 1000. Second section from Photo. S showing a third accessory nucleolus which in this section is attached to one of the chromatic filaments.
Photo. 10. x 1000. Section of an oocyte first order from a receptaculum ovorum, at the same stage of development as those shown in Photos. 1 to 9. The archoplasmic granules are aggregated at two poles of the oocyte bearing a striking resemblance to the polar rings of the ripe egg. Only one pole is shown in the photograph.
Photo. 11. x 1000. Section of germinal vesicle of an oocyte first order from a receptaculum ovorum, showing black chromatic filaments and one accessory nucleolus attached to the longest filament. This was the only accessory nucleolus in this germinal vesicle, and the principal nucleolus stained brownish yellow as in the other oocytes.
Photo. 12. x 710. Young oocyte from ovary showing the large vacuolated nucleolus and well defined areas of archoplasm in the cytoplasm. On the periphery of the photograph is shown part of a very small oocyte with aggregations of archoplasm (yolk nucleus) at opposite poles of the germinal vesicle. Fixative, corrosive sublimate (saturate). Stain, iron haematoxylin.
Photo. 13. X 1000. Part of periphery of oocyte first order from a receptaculum ovorum. The two membranes, with an indication of the substance between, are distinctly shown. The archoplasm is fused with the cytoplasm in a form characteristic of chromo-acetic fixation, c. f. Photo. 10 for platinoosmic fixation. Fixative, chromo-acetic. Stain, iron haematoxylin followed by dilute Bismarck brown.
Photo. 14a. x 1000. Nucleolus with black granules in large unstained oocyte from ovary. The granules resemble the black granules found in the cytoplasm of the same preparation. Fixative, chromo-acetic followed by osmic acid, which blackened the granules of the nucleolus and cytoplasm.
Photo. 14b. x 1000. Nucleolus in a large unstained oocyte from distal end of ovary. Fixative, Hermann's fluid.
Photos. 15, 16 and 17. x 700. Vacuolated nucleoli from large unstained oocytes from ovary. Fixative, Hermann's fluid.
Photo. 18. x 700. Vacuolated nucleolus in medium sized unstained oocyte from ovary. Fixative, Hermann's fluid.
Photos. 19, 20 and 21. x 700. Vacuolated nucleoli in large unstained oocytes from ovary. Photo. 21 shows both a principal and accessory nucleolus. Fixative, picro-nitric followed by osmic acid.
PLATE II.
The section of Photo. 26 is 2 /t. All the others are 2^^ /i.
Photo.s. 22-25. x 1000. Four sections selected from fourteen of a germinal vesicle of an oocyte first order from a receptaculum ovorum. The principal nucleolus is present in three consecutive sections, two of them being shown in Photos. 22 and 23. Photo. 23 shows one accessory nucleolus attached to the largest chromatic filament. Fixative, Rabl's picro-sublimate. Stain, iron haematoxylin, followed by dilute Bismarck brown. 17
238 First Maturation Spindle of Allolobophora Foetida
Photo. 26. X about 1100. Section of upper pole of a first maturation spindle with sphere and centriole in fertilized oocyte from freshly deposited cocoon. There is a centriole at the lower pole of this spindle, but we selected this photograph as more interesting for reproduction, because it is much more difficult to demonstrate a centriole at the upper pole, when it is close to the periphery. Fixative, Flemming's fluid without acetic acid. Stain, iron haematoxylin, followed by dilute Bismarck brown.
Photos. 27 and 28. X 1000. Two sections of the same germinal vesicle of an oocyte first order from a receptaculum ovorum. There are four intervening sections between the two reproduced here and the principal nucleolus of Photo. 27 shows no connection with the chromatic filaments. Fixative, platino-osmic. Stain, iron hsematoxylin followed by dilute Bismarck brown.
Photo. 29. x 1000. Section of a germinal vesicle of an oocyte first order from a receptaculum ovorum, showing the large vacuolated nucleolus and the smaller accessory nucleolus. Fixative, Picro-sublimate. . Stain, iron haematoxylin, followed by dilute Bismarck brown.
Photo. 30. X 1000. Section of a germinal vesicle of an oocyte first order from a receptaculum ovorum showing chromatic filaments in transverse section and two short granular filaments crossing each other. The large vacuolated nucleolus is in the 3rd, 4th and 5th sections from that of Photo. 30. Fixative, corrosive-acetic (5 per cent acetic). Stain, iron haematoxylin followed by dilute Bismarck brown.
Photo. 31. x 1000. Section of a germinal vesicle of an oocyte first order from a receptaculum ovorum showing the large vacuolated nucleolus and an early stage of the segregation of the chromatin into chromatic filaments. Fixative, corrosive sublimate. Stain, iron haematoxylin.
Photo. 32. x 1000. Section of lower pole of second maturation spindle showing four of the eleven chromosomes approaching the lower pole. This section was photographed to show a precocious formation of one of the eleven vesicles not due normally until the telophase. The centriole is in the next section. Fixative, chromo-acetic. Stain, iron haematoxylin.
Photo. 33. X 1000. Section of first maturation spindle, showing five of the eleven chromosomes. This egg is one of eight found in an immature cocoon encircling the cliteilum of a worm. The four chromosomes which are on the same plane are clearly defined and show a decided difference in size. We have six photographs of this spindle showing all the eleven choromosomes but cannot spare space for more than one reproduction. Fixative, corrosive acetic (10 per cent acetic.) Stain, iron haematoxylin, followed by dilute Bismarck brown.
Photo. 34. x 1000. Section of a germinal vesicle of an oocyte first order from a receptaculum ovorum, showing the typically injurious effect of chromo-acetic on the nucleoplasm. This photograph shows a distinct net knot resembling a large nucleolus with two vacuoles, but it is unmistakably an artefact, for the principal nucleolus of this egg is present in the seventh section from the one i*eproduced in this photograph. Stain, iron haematoxylin followed by dilute Bismarck brown.
Photo. 35. x 710. Section of a vacuolated nucleolus of an oocyte from the ovary. Fixative, corrosive sublimate followed by osmic acid. Unstained.
Katharine Foot and E. C. Strobell 239
Photo. 36. x 710. Section of a ring nucleolus of an oocyte from the ovary. Fixative, Lindsay Johnson's fluid. Stain, acid fuchsin.
Photo. 37. x 710. Section of a vacuolated nucleolus. A small accessory nucleolus is also present. Fixative and stain same as Photo. 36.
Photo. 38. x 710. Section of a ring shaped nucleolus of an oocyte from the ovary. Fixative, Merkel's fluid followed by osmic acid. Stain, iron haematoxylin.
Photo. 39. x 710. Section of a vacuolated nucleolus from an ovarian oocyte and near it an accessory nucleolus. Fixative, picro-sulphuric followed by osmic acid. Unstained.
Photo. 40. x 710. Section of a vacuolated nucleolus from an ovarian oocyte and near it a small accessory nucleolus. Fixative, picro-sulphuric followed by osmic acid. Unstained.
Photo. 41. x 710. Section of a vacuolated nucleolus from an ovarian oocyte. This nucleolus appears to be surrounded by a definite membrane and this is shown in three consecutive sections. Fixative, picro-sulphuric. Stain, iron haematoxylin.
Photo. 42. x 710. Section of a vacuolated nucleolus from medium sized ovarian oocyte. Fixative, corrosive sublimate. Stain, iron hsematoxylin.
Photo. 43. x 710. Section of a ring shaped nucleolus in oocyte from a receptaculum ovorum. Fixative, corrosive acetic (10 per cent acetic). Stain, iron haematoxylin followed by dilute Bismarck brown.
Photo. 44. x 710. Section of a ring shaped nucleolus in an ovarian oocyte. Fixative, Graf's picro-formalin followed by osmic acid. Stain, iron haematoxylin.
Photo. 45. x 710. Section of a crescent shaped nucleolus in ovarian oocyte. Fixative, Graf's picro-formalin followed by osmic acid. Unstained.
PLATE in.
All sections 2i/^ /z.
Photos. 46 to 49. X 1000. Four sections selected from eighteen of a germinal vesicle of an oocyte first order from a receptaculum ovorum. Photos. 46 to 48 are consecutive sections, and Photo. 49 is the third section beyond Photo. 48 and is one of three consecutive sections in which the large vacuolated nuoJeolus is present. There are two accessory nucleoli also present in this section. All these sections show the chromatin segregated into more or less definite filaments and Photo. 47 shows a filament with what appears to be a longitudinal split. Fixative, saturate corrosive sublimate. Stain, iron hsematoxylin.
Photo. 50. x 1000. Peripheral section of a germinal vesicle of an oocyte first order from a receptaculum ovorum showing a ring shaped nucleolus. Fixative, platino-osmic. Stain, iron haematoxylin followed by dilute Bismarck brown.
Photos. 51 and 52. x 1000. Two consecutive sections of a germinal vesicle of an oocyte first order from a receptaculum ovorum. Each section shows a ring chromosome, the two differing greatly in size. The prnicipal nucleolus is present in this germinal vesicle and intact. Fixative, saturate corrosive sublimate. Stain, Bismarck brown.
240 Fii-st Ahilunition S|)iii(llc of Allolohopliora Kd'tida
Photos. 53 and 54. ■, iUUU. Each of these phoLograyhs shows one of three consecutive sections of a vacuolated nucleolus in an oocyte first order from a receptaculum ovorum. Fixative, saturate corrosive sul)limate. Stain, iron htpmatoxylin.
Photo. 55. X 710. Section of a nucleolus in an ovarian oocyte. Fixative, bichromate-cupric sulphate. Stain, iron haematoxylin.
Photo. 56. x 1000. Part of a section of a germinal vesicle of an oocyte first order from a receptaculum ovorum showing the principal and the accessory nucleoli. Fixative, platino-osmic. Stain, iron haematoxylin followed by dilute Bismarck brown.
Photo. 57. X 710. Section of a vacuolated nucleolus in an ovarian oocyte. Fixative, bichromate-cupric sulphate. Stain, iron haematoxylin.
PiioTO. 58. X 1000. Section of a germinal vesicle of an oocyte first order from a receptaculum ovorum. This is one of four consecutive sections of the principal nucleolus. Fixative, corrosive acetic (5 per cent acetic). Stain, iron haematoxylin followed by Bismarck brown.
Photos. 59 to 62. x 1000. Four sections selected from sixteen of a germinal vesicle of an oocyte first order from a receptaculum ovorum. The first three sections are consecutive. The prinvipal niicleohis of Photos. 59 and 60 shows no connection with the chromatic filaments. Fixative, Rabl's picrosublimate. Stain, iron haematoxylin followed by Bismarck brown.
Photos. 63 to 65. x 1000. Three sections of a germinal vesicle of an oocyte first order from a receptaculum ovorum. Photo. 63 shows an accessory nucleolus with transverse sections of a chromosome at opposite sides of it. The principal riucleolus is in the sixth section from the accessory nucleolus. In Photo. 64 there is a chromosome in the form of a figure eight and in Photo. 65 a rod shaped chromosome and transverse sections of two more. Fixative, saturate corrosive sublimate. Stain, iron haematoxylin.
Photo. 66. x 1000. Section of a germinal vesicle of an oocyte first order from a receptaculum ovorum showing chromatic filaments and an accessory nucleohis attached to a chromatic filament. Fixative, saturate corrosive sublimate. Stain, iron haematoxylin.
Photo. 67. x 710. Section of a nucleolus of an oocyte from the ovary. Fixative, bichromate-cupric sulphate. Stain, iron haematoxylin.
PLATE IV.
The section of Photo. 76 is 3 // , of Photo. 11 2 /i. and all others on this plate are 2^2 }i.
Photos. 68 to 73. x 1000. Six consecutive sections of an oocyte first order, from the receptaculum ovorum. Photos. 68 to 69 are entire sections unstained. They demonstrate very clearly the presence of the polar-ring substance (yolk-nucleus, archoplasm) and the deuto-plasmic granules blackened by the osmic in the fixative (platino-osmic). In Photos. 70 to 73 only the germinal vesicle and a small part of the surrounding cytoplasm are reproduced. Photo. 70 shows a group of chromosomes. Photo. 71 the principal nucleolus and a small accessory nucleolus. Photo. 72 a large acvcisory nucleolus and a cross shaped chromosome, and Photo. 73 a second section of th3 accessory nucleolus of Photo. 72. Photos. 70 to 73 are stained with iron haematoxyliri followed by dilute Bismarck brown.
Katliarine Foot and E. C. Strobcll 241
Photo. 74. x 710. Section of a vacuolated nucleolus of an oocyte from the ovary. Fixative, corrosive acetic (20 per cent acetic) followed by osmic acid. Unstained.
PiiOTO. 75. X 710. Section of a nucleolus with dark granules. From an oocyte in the ovary. Fixative, picro-acetic followed by osmic acid. Unstained.
Photo. 76. X 710. Section of a small oocyte in the ovary showing the nucleolus and yolk nucleus. Fixative, saturate corrosive sublimate followed by osmic acid. Unstained.
Photo. 77. x about 1100. Section of a nucleolus of an oocyte from the ovary. Fixative, Flemming's fluid (strong). Stain, iron hsematoxylin followed by dilute Bismarck brown.
Photo. 78. x 710. Section of a young oocyte in the ovary showing a ring nucleolus and archoplasm (yolk-nucleus) in the cytoplasm. Fixative, saturate corrosive sublimate. Stain, iron hsematoxylin.
Photo. 79. x 1000. Section of a ring nucleolus of an oocyte from the ovary. Fixative, Merkel's fluid followed by osmic acid. Stain, iron hsematoxylin. (Photo. 8C was omitted by mistake.)
PLATE V.
All sections 2% ^
Photos. 81 and 82. x 1000. Two sections of a germinal vesicle of an oocyte first order from the receptaculum ovorum. This vesicle was cut into nineteen sections and the two reproduced here were fifteen sections apart and both very close to the periphery of the germinal vesicle; the next section on each side being the last to show the germinal vesicle. These photographs show the earliest appearance of the centrioles and asters at opposite poles of the germinal vesicle. The centriole in Photo. 81 is still in contact with the membrane of the vesicle and the centriole in 82 is very close to the membrane. Fixative, chromo-acetic. Stain, iron hfematoxylin followed by dilute Bismarck brown.
Photo. 83. x 1000. Section of a germinal vesicle of an oocyte first order from the receptaculum ovorum. The centriole and aster are further developed than those in Photos. 81 and 82 and not so close to the membrane of. the germinal vesicle. The other centriole is eleven sections from the one in this photograph. Fixative, Boveri's picro-acetic. Stain, iron hsematoxylin followed by dilute Bismarck brown.
Photos. 84 to 89. x 1000. Consecutive sections of a germinal vesicle of an oocyte first order from a receptaculum ovorum. 86 and 87 are photographs of the same section, 86 being taken on the plane of the small centriole, and 87 on a lower plane to show the rest of the chromosomes. The two centrioles are seen at opposite poles in Photos. 84 and 86. There are two accessory nucleoli in Photo. 89. Traces of the persisting membrane of the germinal vesicle are seen in nearly all the sections. Fixative, Rabl's picro-sublimate. Stain, iron hsematoxylin followed by dilute Bismarck brown.
Photos. 90 and 91. x 1000. Two planes of the same section of a first maturation spindle in an oocyte from a receptaculum ovorum, showing four of the eleven chromosomes. Both centrioles are in this section but not on the same plane as the two chromosomes of Photo. 90. One centriole is shown in Photo. 91, which was taken before staining and focused for the unstained
242 First Maturation Spiiullc of Allolohopliora Fatida
centriole at the upper pole, the centriole of the lower pole was not on the same plane. Photo. 91 shows two unstained chromosomes on a different plane from the two in Photo. 90. Fixative, platino-osmic. Stain, Photo. 90 iron hasmatoxylin followed by dilute Bismarck brown. Photo. 91, unstained.
Photos. 92a and b. x 1000. Two consecutive sections of a first maturation spindle of a fertilized oocyte in a freshly deposited cocoon. We have twelve photographs of this spindle showing all the eleven chromosomes and both centrioles. In the two selected for reproduction both centrioles are shown and a few of the chromosomes. 92a was focused for the centriole, sacrificing a sharp definition of the chromosome, and 92b was focused for the peripheral centriole, only one of the four chromosomes being on the same plane. Fixative, chromo-acetic. Stain, iron haematoxylin.
Photos. 93 to 97. X 710. Sections of nucleoli of oocytes from ovary. Fixative, Rabl's picro-sublimate. Stain, iron haimatoxylin.
Photos. 98a and b. x 710 and 1000. Section of a nucleolus of an oocyte from the ovary. Fixative, Platino-osmic. 98a unstained. 98b stained with iron hsematoxylin.
PLATE VI.
The sections in Photos. 99 and 105 are o/j, those of 102 and 106 are 5 ,«, all the others are 2^/^ //.
Photo. 99. x 710. Unstained section of an unfertilized oocyte from a freshly deposited cocoon showing the first maturation spindle at the metaphase, with two of the eleven chromosomes. The peripheral centriole is not visible in this unstained section, but the centriole at the lower pole of the spindle could be clearly seen. Fixative, platino-osmic.
Photo. 100. x 1000. Section of an unfertilized oocyte from an immature cocoon still encircling the clitellum of the worm. This photograph shows the peripheral pole of the first maturation spindle with the centriole and threadlike rays typical of chromo-acetic preparations. The two membranes of the egg with the substance between are clearly defined, and this is shown also in Photo. 99. Fixative, chromo-acetic. Stain, iron hsematoxylin followed by dilute Bismarck brown.
Photo. 101. x 1000. Section showing the centriole at lower pole of a first maturation spindle of an oocyte from the receptaculum ovorum. Fixative, Boveri's picro-acetic. Stain, iron haematoxylin followed by dilute Bismarck brown.
Photo. 102. x 710. Section showing the centriole at peripheral pole of a first maturation spindle of an oocyte from the receptaculum ovorum. Fixative, chromo-acetic. Stain, iron haematoxylin.
Photo. 103. X 1000. Section showing the centriole at the lower pole of a second maturation spindle of a fertilized oocyte from a cocoon. Fixative, chromo-acetic. Stain, iron hsematoxylin.
Photo. 104. X 1000. Section of the second maturation spindle of a fertilized oocyte from a cocoon, showing the centriole at the lower pole, but not in the centre of the sphere. Fixative, chromo-acetic. Stain, iron haematoxylin.
Photo. 105. X about 1000. Section showing the centriole at the lower pole of a second maturation spindle of a fertilized oocyte from a cocoon. Fixative, saturate corrosive sublimate. Stain, iron haematoxylin.
Katharine Foot and E. C. Strobell 243
PiioTO. 106. X 1000. Section showing the centriole at the peripheral pole of a first maturation spindle, of an oocyte from the receptaculum ovorum. Fixative corrosive acetic (10 per cent). Stain, iron hsematoxylin followed by dilute Bismarck brown.
Photo. 107. x 1000. Section of the spindle of one of two small cells of a three celled egg from the cocoon, showing one of the two centrioles. Fixative, chromo-acetic. Stain, iron hseniatoxylin.
Photo. 108. x 710. Section showing the centriole at lower pole of the second maturation spindle of a fertilized oocyte from a cocoon. F'ixative, Merkel's fluid. Stain, iron hematoxylin.
Photo. 109. X about 1100. Section showing centriole at the lower pole of a second maturation spindle of a fertilized oocyte from a cocoon. Fixative chromo-acetic. Stain, iron hsematoxylin.
Photo. 110. x 710. Section of a second cleavage spindle of an egg from a cocoon. Both centrioles are shown though they are not on exactly the same plane. Fixative, chromo-acetic followed by osmic acid. Stain, iron haematoxylin.
PLATES VII, VIII and IX.
The preparations shown in the photographs of these plates are from oocytes from the receptaculum ovorum (except Photo. 128), and were obtained by the method described on p. 200.
The preparations were stained with Bismarck brown.
Magnification of all the photographs, 1000 diameters.
Photos. Ill and 113. Two germinal vesicles each showing a principal nucleolus, one accessory nucleolus and a fine chromatin thread.
Photo. 112. Germinal vesicle showing a pathological aggregation of the chromatin.
Photos. 114 and 115. Two germinal vesicles showing each a principal nucleolus and a longitudinally split spireme. In Photo. 114 there is one, and in Photo. 115 there are two accessory nucleoli.
Photos. IIG to 124. Germinal vesicles showing different forms of the eleven bivalent chromosomes immediately after the transverse division of the spireme, in Photo. 116, two of the bivalent chromosomes are still attached end to end. Nearly all these preparations show a longitudinal split in some of the chromosomes, and in Photos. 116, 118, 121, 122, 123 and 124 both the principal and the accessory nucleoli are present.
Photos. 125, 126, 127, 129 and 130 show the eleven bivalent chromosomes arranged with more or less regularity in the equator of the first maturation spindle. For detailed description of these photographs, see p. 217.
Photo. 128. The eleven chromosomes nearly in the equator of the first maturation spindle of an oocyte from an immature cocoon.
PROPHASES OF FIRST MATURATION SPINDLE OF ALLOLOBOPHORA FOETIDA. foot & strobell photos.
PLATE I.
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AMERICAN JOURNAL OF ANATOMY-VOL. IV.
PROPHAStS OF FIRST MATUK'AIION SPINDLb OF ALLOLOBOPHORA FOETIDA foot s. strohell photos
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PROPHASES OF FIRST MATURATION SPINDLE OF ALLOLOBOPHORA FOETIDA. FOOT & STROBEll PHOTOS.
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PROPHASES OF FIRST MATURATION SPINDLE OF ALLOLOBOPHORA FOETIDA.
FOOT S, STRORELL PHOTOS
PLATE VIII.
AMERICAN JOURNAL OF ANATOMY VOL IV
PROPHASES OF FIRST MATURATION SPINDLE OF ALLOLOBOPHORA FOETIDA. pooT & strobell photos
PLATE IX.
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AMERICAN JOURNAL OF ANATOMY VOL. IV
GEXETIC INTEEPEETATIONS IN THE DOMAIN OF ANATOMY.*
Presidextial Address before the Association of A:\rERicAN
Anatomists.
BY CHARLES-SEDGWICK MINOT, LL. D., D. Sc.
The science of anatomv, altliough one of the oldest of all sciences, was long neglected in x4.merica, and taught only in a routine fashion by professors who had little or no thought for the promotion of the science or any aim higher than teaching a certain number of established facts in gross anatomy to the maximum possible number of students. Within the last generation the few pioneers of anatomy have been succeeded by teachers, many of whom share the highest ideals of anatomical science, and have contributed important discoveries by which it has been really advanced. Our Society is at once the symbol and the outcome of , these comparatively new conditions in America, and we have as our duty not only actively to encourage research, to spread anatomical knowledge, and to earn appreciation of anatomy as a living science, l)ut also to exert a missionary influence l)y which the dignity and vitality of our science shall be brought to recognition at all our universities.
The following recent or new technical terms are used in the course of the address and are recommended for adoption.
Cytogenic glands, false glands which produce cells, as for example, the lymph and genital glands.
Cytomorphosis. to designate comprehensively all the structural modifications which cells or successive generations of cells may undergo from the earliest undifferentiated stage to their final destruction.
False glands, all glands, which develop without ducts.
Lymphwum, a more or less definitely circumscribed area consisting of cellular reticulum, the meshes of which are charged with leucocytes and are in direct communication with lymph-vessels or more rarely with blood-vessels. It is a site for the multiplication of leucocytes.
Mesepatium. the membrane (French, mcso) extending from the stomach and duodenum to the median line of the ventral abdominal wall, and in which the liver develops. It comprises a dorsal mesepatium (lesser omentum) and ventral mesepatium (falciform or suspensory ligament). American' Journal of Anatomy. — Vol. IV.
246 Genetic Interprt'tations in the Doinain of Anatomy
It is sonictinies said, and perliaps inoro often thouglit, tliat anatomy is a completed science. This assertion is based upon the thoroughness and exhaustive character of the descriptions to be found in our textbooks of the anatomical conditions in the human adult; yet even as regards the organization of the adult we have still much to learn, especially concerning the microscopic structure with which we are still very imperfectly acquainted.
But anatomy is not alone a descriptive science. It is also comparative and genetic. In both these directions its development is very far from complete, and a vast amount of original research must still be completed before comparative anatomy and embryology shall have approached anywhere near even the present perfection of descriptive human anatomy.
To embryological research must be attributed a large part of the extraordinary progress Avliich anatomy lias made during the last twentyfive years. By embryology we have gained a far deeper understanding of all anatomical forms, we have acquired new interpretations for pathological facts, and we have secured for the first time some clear insight into the essential structure of the brain. I need not do more than allude to these achievements, since they are familiar to us all, and have most profoundly affected our anatomical conceptions. Our point of view has changed, and we interpret the anatomy of the adult in terms of the genesis of the organs and tissues during their embryonic development.
Perhaps no man has contributed so much towards this result as the great Leipzig anatomist, Wilhelm His, whose death this year we have to lament. He was a great master. He had full command over the problems of anatomy and contributed in the richest measure to their solution. His influence in America has been especially strong and widespread, and has certainly had much to do in bringing about the progress of anatomy in this country, which we are seeking to maintain, and if possible, increase. In what I have to say to you on this occasion, you will perceive
Phrenic area, the area on the superior or cephalad surface of the liver, by •which the liver is attached permanently to the diaphragm. It includes the whole of the territory of the coronary and triangular " ligaments," socalled in current text-books.
Sinusoid, an irregular blood space, produced by the subdivision of a larger blood-vessel by the ingrowth of the parenchyma of an adjacent organ.
Structural unit, the territory of an organ supplied by a single terminal branch of an afferent vessel (artery or vein) ; the volume of such a unit is often only 10-20 cubic millimeters.
Trophoderm, the special layer of cells formed on the exterior of the young mammalian blastocyst, and serving to secure the implantation of the ovum in the uterus.
Charles-Sedgwick Minot 2-i7
the influence of His clearly, and I cannot let the opportunity pass of expressing publicly my gratitude and admiration for the greatest anatomist of his time.
Although embryology has already contributed in so ample measure to the promotion of our science, we are still far from having accepted all the enlightenment which she offers us. With your permission I will try to present to you certain embryological aspects of anatomy, the character of which I have sought to indicate in the title of this address, by the words " genetic interpretations."
First of all, let us consider the subject of cytomorphosis. This word I proposed in 1901 ^ '"to designate comprehensively all the structural modifications which cells or successive generations of cells may undergo from the earliest undifferentiated stage to their final destruction." As stated on that occasion it is convenient, though somewhat arbitrary, to distinguish four fundamental successive stages of cytomorphosis. These stages are (1) the undifferentiated stage: (3) the stage of progressive differentiation, which itself often comprises many successive stages; (3) the regressive stage or that during which degeneration or necrobiosis occurs; and (4) the stage of the removal of the dead material. The general data on which the conception of cytomorphosis is based have been briefly put together also in my text-book of embryology, and it seems therefore superfluous to dwell upon them at length in addressing you.
I cannot of course claim any greater originality in the establishment of the conception of cytomorphosis than is implied by the definite formulation of the ideas upon which it is based. These ideas have been gradually gathered as the fruit of numerous investigations in histogenesis. The mentioned investigations have made us all familiar with the conception of undifferentiated embryonic cells, with the gradual progress of differentiation in the cells during the emljryonic, foetal, and even postnatal periods; and have also made us acquainted with various examples of degeneration and atrophy occurring in the course of development, both before and after birth. Up to the time when I proposed the term there had been, so far as I know, no attempt to survey all this array of facts from a single unifying point of view. But such a point of view is, I believe, well calculated to render our notions more precise as to many processes of development, and to afford us at the same time the practical benefit of being able to present the facts of histogenesis in our teaching in a wav, which is very advantageous, because it facilitates in the student's mind the establishment of a real insight into the general course of development by emphasizing principles of very wide application. To me, nt least, it seems that the conception of cytomorphosis should be made the
248 (ionetic Interpretations in the Domain of Anatomy
foundation of all our instruction in anatoni}', and that its importance should be constantly emphasized in our chiss-rooms and that when good illustrations of cytomorphosis are encountei-ed by the student, his attention should be especially directed to them, so that he may become familiar with the conception. Let me mention a few illustrations which I have found serviceable in teaching.
But first I must call your attention to an aspect of cytomorphosis, which has not hitherto, so far as my knowledge goes, been sufficiently emphazised. We may distinguish two fundamental phases. During the first, cell division occurs, during the second, cell division does not occur. During the first phase we may find a progressive alteration, which gradually takes place in successive generations of cells, but apparently the amount of differentiation which can occur while cells retain the power of active division is comparatively slight. During the second phase, since the cell no longer divides, the alteration takes place in the single cell, and the alteration, which occurs under these conditions, is typically great and may be best designated by the term final differentiation, difl'erentiation being here held in our minds clearly distinct from degeneration. By final differentiation we mean the establishment of that special organization of a cell, which brings to perfection the specialized physiological function for which the cell is destined. Thus the alteration of a mesenchymal cell into a muscle fibre is its final differentiation, and establishes the physiological perfection of that cell as a contractile element. Beyond the final differentiation of the cell comes the series of degenerative changes. A comprehensive study of cell degeneration is yet to be made, nevertheless we can already say that, although cell degeneration is chiefly characteristic of the second phase of cytomorphosis, which is also characterized by the cessation of cell division, yet the degeneration may be initiated before the power of cell division is lost and the degenerative change in the cells may go on while they are still proliferating; but topically it seems rather that degeneration belongs to the second phase of cytomorphosis, and this seems to be alike true for necrosis and atrophy, that is to say, simple cell death, and for necrobiosis, that is to say, cell death preceded by structural changes, which we know commonly under the name of hypertrophic degeneration.
Let us pass on now to a few illustrations of cytomorphosis:
The first to which 1 would direct your attention is afforded by the
formation of the " trophodenii." This is a new term which 1 have
recently brought forward to designate the special layer of cells formed
apparentlv from the ectoderm (or according to Assheton's theory, from
('hai-los-Sedgwick :\Iinot 249
the oiitddei'iii ) which st"i\os to secure tlie iinphiiitation of the maininaliaii ovum in tlie walls of the uterus. In my "' Text-Book of Eml)ryology " 1 have tigured these eells'l'rom the human ovum and ai)i)lied to them the term trophohlast, hut as Professor Huhrecht. who introduced this last term into science, luis ol)jected to this application of it, it has heen necessai-y to inti'oduce a new term, hence the designation trophoderm. It corres])on(ls in lai-ge part, perhaps wholly, to that which Duval designated as the ectoplacenta. It is tlie first tissue in tlie manunals to ho distinctly differentiated. The cells hy their large size, distinct boundaries, and characteristic nuclei, are readily distinguished from any other cells existing in the embryo at the time the trophoderm is differentiated. Very soon after the development of the trophodermic cells, a large part of them begin to complete their cytomorphosis by undergoing degeneration and resorption. By their disappearance, as I have elsewhere pointed out, the intervillous spaces arise. The trophoderm therefore is not only the earliest tissue to be specialized in the development of mammals, but also the earliest tissue to absolutely complete its cytomorphosis.
Another striking illustration of the cytomorphic cycle with its phases of differentiation, degeneration, and disappearance of cells is offered to us by the blood corpuscles. The first blood cor])usclcs are cells with a minimum amount of ])rotoplasm. The cells then proceed togrow, and as they grow, differentiate themselves in part at least, into red blood glo1)ules. In mamnuils there follows the stage, degenerative in character, by which the nucleus of these red blood corpuscles disappears. The manner of its disa]ipcarance is, to be sure, still perhaps a matter of debate, but for as for the moment is of minor importance. After the degeneration or disappearance of the nucleus, the blood corpuscles are destroyed and, having completed their cytomorphosis, are replaced by fresh ones.
A third admirable illustration is offered ns by cartilage, and a fourth bv bone. In cartilage we see at first a differentiation of simple mesenchvmal cells which then enlarge, becoming the characteristic cartilage cells. When ossification of the cartilage occurs we can easily follow the hypertrophic degeneration of these same cartilage cells, which has been so much studied that good accounts of the enlargement and breaking down of these cells preliminary to the ingrowth of the osteogenetic tissue can be found in all the better text-books of histology; but 1 regret to say I do not recall any text-hook either of anatomy, histology, or embryology, which ]>oints out the fact that this succession of changes in cartilage cells is a typical and almost perfect illustration of cytomorphosis. Almost the same can be said <>r hduc. for in the formation of this tissue also we have first, the difl'ei-ciit iatiiui of the mesenchymal cells into osteoblasts, which
2")0 Genetic Initerpretatioiis in tlie Domain of Anatomy
are always of larger dimensions than the cells fi-om Avliicli they arise; and after these osteoblasts have lieeome bone cells they cease their development and apparently degenerate. I have to say apparently . because, so far as I know, the fate of the bone corpuscle has not been ascertained with certainty. We risk but little, however, in asserting that the bone cells also offer an instance of a normal, complete cytomorphosis.
As a fifth and last illustration, let us choose the epidermis, in which Ave have a distinct type of differentiation. In the basal layer are the cells, which divide and produce, according to our present notions, all of the cells of the epidermis. When the basal layer cells divide, however, some of them only, pass immediately through further cytomorphic changes in order to make first, the cells of the mucous layer, and later, by undergoing cornification, to constitute the horny layer. Others of the basal cells remain members of the basal layer and continue to proliferate. We thus see the progeny of the original basal cells divided into two classes: the cells of one class pass on in their development, the others retain their ancestral type. In the epidermal cells we observe as in other instances of cytomorphosis, first the enlargement and differentiation of the cells, here occurring in the mucous layer, and later their degeneration or cornification followed by their necrosis and destruction.
It would be easy to multiply these illustrations. All of you could supply more. That which I would urge upon your consideration is the value of the cytomorphic interpretation in explaining the origin and differentiation of tissues in the light of the broadest principle of cellular development which we have up to the present time been able to establish.
I will now ask you to consider certain possible genetic classifications. The most fundamental and important of these seems to me to be that of tissues and of organs according to the germ layers from which they arise. This classification was made the basis of his entire course of lectures upon animal morphology by Professor Carl Semper, the Wiirzburg zoologist, under Avhom I had the pleasure of studying in 1875-76. It is not merely very practical and advantageous alike to teacher and pupil, but is also the only thoroughly scientific classification of structures and organs which we can adopt. No other classification should, in my judgment, be seriously considered. So firmly do I hold this conviction that I greatly deplore the fact that our text-books of histology are not written upon an embryological basis, the lack of which deprives them of much of the scientific character and value they ought to have.
As our knowledge of the development from the germ layers has grown, we have learned with ever-increasing certainty that each germ layer has its specific role to pla}^ Each germ layer produces its own specific
Charles-Sedgwick Minot 251
set of tissues, which are not duplicated by the tissues of any other germ layer. I have already pointed out on another occasion that the importance of the germ layers is as absolute and unvarying in the domain of pathology as in normal differentiation; I need not dwell on that aspect of the question now, but will only repeat the declaration of my belief that the entire teaching of the pathologist as well as of the histologist and anatomist should be based on the doctrine of the germ layers and their specific roles in histogenesis.
Almost any group of tissues would offer a favorable opportunity for the discussion of genetic classification. We may select those which are differentiated from the embryonic mesenchyma and which are commonly grouped in the adult under the names of the connective and supporting tissues. It is almost superfluous, so much is the genetic point of view neglected, to call your attention to the fact that in our current text-books of histology there is often little or nothing which would enable the student to grasp the relations of these tissues to one another or to understand their genetic relationships. It is true that our knowledge in spite of the great advances of recent years is still too incomplete to justify our asserting that the classification which we can now make is final. Kevertheless we can already perhaps attain approximate finality. A very great step in advance was made when the character of the cellular reticulum was established and it was shown that this tissue is different from ordinary connective tissue. It has two principal characteristics : first, the matrix or intercellular substance is nearly or absolutely fluid, so that leucocytes can wander freely in the intercellular spaces of the reticulum; second, the network of original protoplasmic filaments has become directly converted into a network preserving more or less the original form, but consisting not of protoplasm, but of a new chemical substance, reticulin. Where cellular reticulum is developed, as for instance in the so-called adenoid tissue, there may be formed from the cells a minimum amount of connective tissue fibrils and of elastic substance, but if we may judge from our present knowledge the cells, which have produced reticulin, preserve but a very small capacity for the production of other elements of connective tissue. Hence, it seems to me that we may well put cellular reticulum in a class by itself, quite apart from the true connective tissues in which the intercellular substance is not mainly fluid and in which there is an abundant development of fibrillar or elastic substance, or of both, and in which, further, reticulin is nearly if not wholly absent. We shall thus come to place all the connective tissues, properly so-called, in a second genetic group. When we follow in the embryo the history of young connective tissue, we learn that it undergoes two principal kinds of modifica
'^.")v (u'lu'tic I iitci'prctnt ions in llic |)(iiii;iiii of Anatoiny
tidiis. tlinsc iiircct iiii:' the iii;iti-i.\, aiid lliosc nll'cci iiiii' the cells. On these (liircrcuccs tlic clnssilical i<ni in the Inllowiiiu- tahic is hascd.
We also know lliat eoimeetixe tissue can l)e diret'tly 1 ransfornicd into cartilage, which. Ihererore. iiii(|uestional)]y helongs in the same second genetic gT()ii|) as the true connective tissues. .\s regai'ds hone, 1 find it souiewliat dilHciilt to i-eaeh a decision, hut incline to the conclusion that hone should he regarded as distinct from the true connective tissue, thus nuiking a third genetic division of the tissues derived from the primitive mesenchynia. 'I'liis conclusion a])i)eals to me partly as a protest against the ahsurd, though long estahlished and honored, custom of separating cartilage from connective tissue, and putting cartilage and hone together in a common grouj) under the head of supporting tissues. The following tal)le presents the ])i'o])osed classification in a form which you can easily follow :
MESENCHYMA.i
TABLE I.— THE MESENCHYMAL TISSUES.
Cellular reticulum TMucous tissue
' Matrix specialized.-^ Adult connective tissue I Cartilage
Embryonic connective tissue ■
Cells specialized
.Bone
Fat cells Pigment cells Smooth muscles Basement membranes Pseudo-endothelium
I Genital interstitial cells,
L etc.
Let me refer hriefiy to a third and more special example of the genetic t-lassification of tissues, namely, that of the hlood-vessels. As you probably all know% recent embryological investigations have compelled us to recognize not only the three familiar and long-known classes of bloodvessels, arteries, veins, and capillaries, but also a fourth class, that of the sinusoids. Capillaries arise as small vascular sprouts from pre-existing vessels, and these sprouts grow in the mesenchyma. A sinusoid, on the contrary, has an entirely dift'erent developmental history, for it is ]u-oduced by the subdivision of a ])re-existing and relatively large vessel. The sul)division is accom])lished by the ]u-oliferating tubules (or trabecuUp) of an organ, which encounter a large vessel and invade its lumen, pushing the endothelium before them. The endothelium of the vessel, on the other hand. ex])ands and spreads over the tubules (or tral)ec-uhv)By the convolutions and anastomoses thus produced, a large vessel is subdivided into small ones. It follows that a sinusoi(hil circulation is ])urely venous or ])urely arterial, it may sultit'c. upon this occasion, to ]toint out again that the structure of numy impoi'tant organs, as for
Charles-Sedgwick Minot 253
example, the liver and Wolffian body, cannot be understood or even described correctly without taking into consideration the sinusoidal character of their circulation. In this case also, the adoption of the genetic interpretation is much needed. We shall apply presently the concept " sinusoid '■' to aid us in the interpretation of glands.
We may pass now from a consideration of tissues to that of organs, and begin with the glands. The classification, which at the present time prevails vfidely, is one based upon certain incidental peculiarities in the shape of the secretory portion of the glands, so that they are put into two main divisions : the tubular and alveolar; then under each of these we have three main parallel groups :
the simple tubular or alveolar glands;
the simple branched tubular or alveolar glands ;
the compound branched tubular or alveolar glands.
But in this classification there is no place for such a gland as the liver and the thyroid. In text-books of histology, we find the liver tucked in under the tubular glands and designated as a reticulated tubular gland, and the thyroid placed as a follicular gland under the head of the alveolar. But in another way the system also fails, for there are tubulo-alveolar glands which again must be classified as simple, simple branched, or compound branched. Essentially this classification is adopted by the authors of the manuals of histology which I have examined. To classify glands thus, seems to me about on a par with classifying organs by their being solid or hollow, a principle, which would put the spinal cord in the same class with the intestine, and nerves in the same class with the tendons. The peculiarities of shape of the secretary portions of glands are entirely secondary, and do not indicate anything fundamental in regard to the structure of the gland itself. We cannot call a system good which, if applied in accordance with its own definitions, would put some of the mucous glands of the stomach in one division, others in another division, because, although these glands are alike in their histological structure, some of them are branched and some are not. Must we not condemn a view, which excludes the ovary from the glands and makes the testis a compound tubular gland, although ovary and testis are strictly homologous organs, even in the details of their structure? These are only samples of the innumerable difficulties which the system encounters, -because it is essentially pedantic, admirable as an orderly arrangement of names, but impossible as a presentation of anatomical facts.
It appears to me not difficult to make an entirely new classification of 18
254 Genetic Interpretations in the Domain of Anatomy
glands, which shall be based upon their genesis and upon the morphological distinctions, which exist between them. To begin with, we may put the unicellular glands, of which the goblet-cells serve as the most familiar type known in man, in the Class A, v. p. 25G; next we may have the true multicellular glands of the epithelial type, which always develop with ducts by which their secretion is discharged; these form Class B; while a third class would include the false glands which never develop with ducts, which produce either merely an internal secretion so-called, or are adapted to the development of cells of special kinds, as, for example, the lymph- and genital-glands; such structures constitute Class C.
We must first attempt a classification more in detail of the true epithelial glands (Class B). In my opinion Ave can best make two fundamental divisions. The glands of the first division have often been called single or simple follicular glands ; I propose for them the term " simple glands." The glands in question are always small and have one or several centers of growth according as they are simple tubes or slightly branching. Those of each kind are always very numerous and they occur more or less near together over considerable areas. There are two types of these known. The first are simple invaginated areas with scattered unicellular glands, as for instance the glands of the large intestine, the so-called Lieberkiihn's follicles; they might be called simple follicles. Glands of the second type are invaginated areas with specialization of the cells, as, for example, the sweat, gastric, and sebaceous glands; they might be called glandular follicles. In the accompanying table the principal glands of this division are enumerated.
The glands of the second division are of greater bulk and are often referred to as organic or branching glands. I propose to name them " compound glands." They are provided with a single main duct, which is more or less freely branched, each branch connecting finally with the secretory portion proper of the organ, which portion may itself also be branched or not. Each gland falling in this division is a more or less complete organ by itself, receiving its special blood supply, and its special innervation — is, in short, a clearly marked physiological entity. Such a gland differs profoundly in its plan of organization from the glands of our first division. Of the second division there are clearly three main types to be distinguished. In the first type the branches of the glands are found to be supported by mesenchyma or its derivative, connective tissue, which is more or less abundant between the ducts and secretory elements of the organ, and in the mesenchyma there is a capillary circulation, which is often brought, however, into.. intimate proximity with the epithelial elements of the organ. These organs are further character
Charles-Sedgwick Minot 255
ized by tlie fact that their branches remain distinct. In the second type, on the other hand, the branches unite togetlier and form an anastomosing gland structure, and when this anastomosing condition is found it is associated, not with the development of connective tissue and capillaries, between the epithelial elements of the organ, but, on the contrary, Avith the presence of a sinusoidal circulation. The branching glands with capillary circulation are numerous, and they may arise, as is noted in the table, from either the ectoderm, the entoderm, or the mesothelium. Glands of the second type, anastomosing and furnished with sinusoids, are few in number. The liver is, of course, the most typical and the most important. With the liver we ought perhaps to associate the paraphysis, for the recent and still unpublished investigations of Dr. John Warren show that when this gland is highly developed it is of an anastomosing t}pe, and make it probable that its blood supply is sinusoidal.
There remains still a third type, which is necessary, because the ducts become obliterated in a certain number of true epithelial glands, which develop primarily with ducts. There results in each case a group of hollow epithelial follicles, which are characteristic. For this type I propose the name, " ductless epithelial glands." The thyroid gland and the hypophysis are probably the best-known illustrations of this group of glands. Although the morphology of the pineal gland (epiphysis) is obscure, the organ seems at present to belong to our third type.
Our third Class, C, comprises the false glands, which never develop with ducts. So far as I am aware this statement may be made absolute for all glands of this class. It is true beyond any possible question for most of the glands, which are here to be considered, but it is perhaps as well to note that possibly some of the glands of the first division may be found in some vertebrates to have been primitively provided with ducts. This seems to me possible, but not probable. The first division of the false glands are the epithelioid. They are perhaps exclusively, so far as the essential gland elements are concerned, of entodermal origin, and it has become probable that their circulation is typically sinusoidal. In the present state of our knowledge it would be venturesome to make positive assertions on these two points. In the epithelioid glands we have groups of cells of epithelial origin separated, in the adult at least, from the layer which produced tliem, and brought into intimate relation with blood-vessels. A second division comprises the mesenchymal ductless glands, which are similar to the epithelioid glands in their general appearance, but their specific elements are derived from the middle germ layer. x\s an illustration of the duct^-.ss false gland of the first division, I may mention the parathyroid; of the second division, the suprarenal cortex. As
256 Genetic Interpretations in the Domain of Anatomy
to the position of the thymus, I feel quite uncertain and hardly dare to say whether it should be placed among the epithelioid glands or among the cell-producing glands. Similarly, how to place the interstitial cells of the genital glands in our system is not yet quite clear to me. The third division is that of the cytogenic glands, and of these we may readily distinguish three important types : the first, those in which lymph cells arise ; second, those which produce red blood corpuscles ; and third, those which yield the genital elements. The glands of the first type may be called lymphseal structures. " Lymphajal " is a new term derived from " Lymphseum," itself a new technical expression, which I have used for severr.l years in my lectures on histology and have found advantageous. A lymphgeum may be defined as follows : it is a site for the multiplication of leucocytes and is a more or less definitely circumscribed area consisting of cellular reticulum, the meshes of which are charged with leucocytes and are in direct communication Avith lymph-vessels, or more rarely Avith blood-vcf^sels. The following offer examples of lymphasa: solitary follicles, tonsils, thymus, lymph glands, hsemolymph glands and spleen. As stated above, whether the thymus should belong in the first or third division, I cannot say. Of the second type in this division, the bone marrow is the most important example. Of the third type, that of the genital glands, we have of course to distinguish two forms, the ovary and the testis.
With these explanations, I hope the accompanying table will be clear and I trust that the proposed new classification of glands will seem to you both more scientific and more available than the classification now prevalent, which I should like to see displaced.
TABLE II. CLASSIFICATION OF GLANDS.=
Class A. Unicellular.
Class B. True Glands, always developed with ducts.
Division 1. Simple Olands, {unifollicular or single glands).
a. Ectodermal.
1. Sweat glands.
2. Sebaceous glands.
3. Buccal glands.
b. Entodermal.
1. CEsophageal.
2. Gastric.
3. Intestinal.
c. Mesothelial.
1. Uterine.
Charles-Sedgwick Minot 357
Division 2. Compound Glands {organic or true compound glands). Type a, ductless epithelial branching {with capillary circulation).
1. Ectodermal. .
Salivaries, tear gland, Harderian. Mammary glands.
2. Entodermal. Pancreas.
3. Mesothelial.
Appendicular glands of the urogenital system. Type b, anastomosing {with sinusoidal circulation).
1. Liver.
2. Paraphysis (in Necturus).
Type c, ductless epithelial {with secondary ohliteration of duct).
1. Thyroid.
2. Hypophysal gland.
3. Infundibular gland.
4. Pineal {epiphysis).
Class C. False Glands, never developed with ducts.
Division 1. Epithelioid glands {exclusively entodermal?)
1. Parathyroid.
2. Carotid.
3. Thymus (cf. below) (?).
Division 2. Mesenchymal ductless glands.
1. Suprarenal cortex.
2. Coccygeal gland and other chromaffinic cell organs.
3. Interstitial cells of genital glands (?).
Division 3. Cytogenic glands.
a. Lymphseal structures.
1. Lymph glands and follicles (tonsil?).
2. H^molymph glands.
3. Spleen.
4. Thymus (?).
b. Sanguifactive organs.
1. Bone marrow.
c. Genital glands.
1. Ovary.
2. Testis.
I should like to include, in passing, reference to another general anatomical conception which, though not based strictly on embryological results, may be appropriately mentioned. I mean that unit of adult organization, which is sometimes referred to as the " lolule," but, as this term is somewhat confusing owing to the manifold meanings assigned to it, I venture to express the hope that the term structural unit " will be
258 Genetic Interpretations in the Domain of Anatomy
used instead, as has already been done by a few writers. We can then continue to employ the term lobule for the hing and the liver in the senses tradition gives to the term, as used for these two organs, and avoid confusion. The structural unit ' may be defined as the territory of an organ supplied by a single terminal branch of an afferent vessel (artery or vein). The volume of such a unit is often only 10-20 cubic millimeters. In the case of the liver, the structural unit comprises parts of several adjacent so-called lobules. It is a pleasure to recall that the recognition of the anatomical importance of these units is due to one of our most distinguished American investigators. Dr. Mall.
Finally, I should like to apply the principle of genetic interpretation to descriptive anatomy. It will, I think, sufficiently expound the point of view I am advocating to consider the application of the principle to a single organ, and for this purpose we may conveniently select the liver. In order to show that what I propose is practically a real and great innovation, let me indicate to you briefly the character of the anatomical descriptions of the liver to be found in some of the leading text-books of human anatomy.
In Cunningham's Anatomy (1902), the account of the liver is written by Professor Birmingham. He describes, 1, the general form of the surface ; 2, the topographical relations and surfaces in detail ; 3, the fissures, without giving their morphological relations; 4, the division into right and left chief lobes ; 5, the peritoneal relations and ligaments ; 6, the physical characteristics. ■ In the tenth edition of Quain's Anatomy (1896), the description opens,
1, with the dimensions and weight; 2, the surfaces; 3, the fissures; 4, the ligaments and the omentum; 5, the topographical relations; 6, vessels and nerves; 7, the ducts.
Testut in the third volume of his Anatomy (1894) gives, 1, the situation ; 2, fixation ; 3, volume and weight ; 4, general confirmation, including the two chief right and left lobes ; 5, the surfaces in detail.
The account of the liver in Poirier's Anatomy, A^olume IV (1895), is written by Charpy, who begins with 1, the definition, and continues with
2, situation ; 3, fixation ; 4, data as to weight, consistency, etc. ; 5, the form and surfaces. Under the head of fixation Charpy says :
" La foie est suspendu a la voute du diaphragme par deux moyens d'attache: par des replis peritoneaux et par la veine cave inferieiire. '
This misleading statement is the more deplorable because he mentions only incidentally that the liver adheres directly to the diaphragm. Quite at the end, the division into the right and left lobes is mentioned.
Charles-Sedgwick Minot 259
In tlio fourth edition (1901) of ]\Ierkel-Henle's Grimdriss, there is, 1, a general account, which is distinctly not morphological in character; 2, detailed description of the surfaces and topography; 3, of the histology.
Gegenbaur in the seventli edition of his Anatomy (1899) proceeds very differently, for he has strong morphological inclinations. He gives, 1, the general account of the development of the liver; 2, general account of the surfaces, including the division into the chief lobes; 3, the relation of the veins to the omentum and the falciform ligament. Gegenbaur is the only author of a text-ljook of human anatomy, known to me, who gives a distinctly morphological account of thq human liver, but even his presentation of the subject leaves much to be desired, chiefly because his knowledge of embryology was meagre, and quite insufficient for an adequate interpretation.
It would be easy to analyze descriptions in other text-books, but enough has been presented to show that they are usually characterized by certain common tendencies. The authors dwell upon the position and shape of the liver, seeking to emphasize its exact form, but not endeavoring at all to emphasize the essential characteristics of the organ, or to bring out the significance of its parts in a manner satisfactory to either an embryologist, a physiologist, a morphologist, or a pathologist. With the exception of Gegenbaur, none of the accounts rises above the level of sheer description.^ They simply perpetuate the tradition inherited from the time when human anatomy Avas only the description of what was actually found in the human adult. That tradition has undoubtedly been in part maintained by the demands of surgeons, whose interest is necessarily chiefly given to the exact determination of the topographical divisions in the body, hence the influence of the surgeons, when dominant in the anatomical laboratory, has often exerted an influence unfavorable to the becoming maintenance of a scientific spirit, such as we ought to insist upon for the sake alike of anatomy and medicine.
If we review collective!}- the brief analyses just given of the actual descriptions in the text-books, we realize at once that those points, which the genesis of the liver reveals to us as fundamental, are scarcely heeded by the authors whom we have reviewed. This is not a fitting occasion to attempt a new description of the liver, and I can merely indicate to you the principal points upon which a scientific description ought, in my opinion, to be based. No little study and care woidd be necessary to work out practically the suggestions, embodied in the following schedule. Indeed, the schedule can doubtless be improved by others.
In order to prepare an adequate description of the liver, we must begin by laying aside certain bad habits which we have inherited and have
260 Genetic Interpretations in the Domain of Anatomy
allowed ourselves to perpetuate. I mean the habit of applying the term ligaments,, and the habit of applying the term fissures, to the liver ; also the habit of describing the hepatic segment of the vena cava inferior as a vessel distinct from the liver, it being in reality, strictly, in every sense of the word, a portion of the organ. It may be further suggested that the introduction of a new term, mesepatium, may assist in clarifying the relations. The "mesepatium" is the membrane (French meso), which stretches from the ventral border of the stomach and duodenum to the median line of the ventral abdominal wall. It is in this membrane that the liver develops. Above the liver, between it and the stomach, is the dorsal mesepatium (lesser omentum). Between the liver and the body wall is the ventral mesepatium (falciform or suspensory ligament). Instead of speaking of the ligaments, we should speak of the insertion of the dorsal and ventral mesepatium into the liver ; and instead of coronary and triangular ligaments, we should speak of the attachment of the liver to the diaphragm. This area of attachment might be called, as regards the diaphragm, the hepatic area, as regards the liver, the phrenic area.
With these preliminary explanations in mind, it may be suggested that a description of the liver must begin, as many authors have begun it already, with a general statement in regard to the position, size, color, and general form of the organ, and explaining that it is a gland, with a duct opening into the duodenum, and having the gall bladder appended to it, and that the circulation is sinusoidal, and not capillary.
Next, I should place a careful statement of the fundamental relations, as follows, first, of the broad connection of the liver with the diaphragm. This connection is primitive embryologically, is maintained throughout life and constitutes the phrenic area. It is not by the so-called ligaments or peritoneal folds, nor is it by the vena cava inferior that the liver is attached ic the diaphragm. On the contrary it is by a large and characteristically shaped phrenic area of the organ that the connection is established. Second, the relation of the liver to the mesepatium, pointing out especially that the insertions of the dorsal and ventral mesepatia mark the division of the liver into right and left lobes and that the insertion is enlarged at one point towards the right to form the so-called porta of the liver, which admits from the dorsal mesepatium the hepatic artery, bile duct, and portal vein. Third, the relation of the veins to the organ, emphasizing that the portal vein marks the border of the dorsal mesepatium, and that its branches within the organ mark the so-called portal canals; emphasizing also that the umbilical vein or venous ligament marks the free edge of the ventral mesepatium, and explains the position.
Charles-Sedgwick Minot 361
origin and adult state of the ductus venosus. Fourth, the entrance and exit of the vena cava inferior. In this connection there should be made clear the role of the caval mesentery in furnishing a path for the cava inferior, and at the same time shutting off the lesser peritoneal space, and keeping the surface of the Spigelian lobe as part of the boundary of this space.
Next, again, might be presented the secondary features, especially the marking off of the caudate lobe from the chief right lobe by the vena cava inferior, and the marking off, similarly, of the quadrate lobe b}' the porta and the gall bladder.
Finally, according to this schedule, the description of the finer surface modelling and the contact with various adjacent organs, such as the stomach, colon, duodenum and kidney. Not one of these topographical relations is indispensable for a comprehension of the general character of the organ. Even from the standpoint of the surgeon and physician they are of minor importance. If they are put, as has been customary, in the forefront of text-book descriptions, attention is distracted from more essential things. Surely one need not argue to prove that a general comprehension of each organ is, first and last, the most important goal, to be striven for in the study of it.
In regard to almost every organ in the body it may be said, I think without injustice, that the current anatomical text-books offer bare and barren form-descriptions, seldom giving much, and often giving no, consideration to the essential morphological features of the parts. Take, for example, the urogenital system. We all know that the internal female genitalia are formed of two urogenital ridges, which fuse in the median line, making the so-called genital cord. There is in each ridge a longitudinal epithelial duct, which becomes the Fallopian tube, and by fusing with its fellow in the genital cord, produces the cavity of the uterus and vagina. A projection on one side of each ridge forms the ovary. Where the ridges have not united, rudiments of the Wolffian body of the embryo occur. The surface of the ridges, both where they are separate and where they are united, is covered by mesothelium. Around the duct (Fallopian tube), there is developed a muscular layer, and around the uterine portion of the fused ducts in the female a very powerful musculature is developed. By the union of the two ridges a partition is formed across the pelvic end of the abdomen, so that the abdominal cavity forms a pocket on the dorsal, and another on the ventral, side of the genitalia. Now the anatomical way of describing these organs is not to mention the ridges at all, but in the case of the female to speak of the uterus and its liga
262 Genetic Interpretations in the Domain of Anatomy
ments. It seems sometimes as if a deliberate effort were made by the descriptive anatomist to exclude all liberal use of the understanding and of the intelligence from the study of anatomy, and to reduce it ahnost to mere memorization of shapes and proportions, exceedingly difficult to fix in the mind by that method.
Is one not justified in condemning with great severity the perpetuation of this old type of anatomy ? Is it not a grave mistake to fail to take advantage of the progress of anatomical science, and to utilize the best results of anatomical investigation to aid us in forming for ourselves, and still more, perhaps, for our students, clear notions of the essential characteristics of human organization? There has been within the last twentyfive years a very great progress in our knowledge of the topographical anatomy of the viscera, both thoracic and abdominal. When I plead for the presentation of the subject from the genetic standpoint, I do not mean to imply- that this superior topographical knowledge should be slighted, but, on the contrary, I believe that if the student can first master the essential morphological relations of the body, it will be easier for him to master subsequently the finer, and often practically important, topographical details. Let our motto be, not " to memorize," but " to comprehend " the facts of anatomy.
Embiyology illuminates anatomy. Its teachings give us the intellectual mastery of anatomical science, because embryology analyzes details, discriminates the essential from the secondary facts, and establishes the genetic interpretation, in the solvent light of which the obscurities of ancient . anatomy vanish, and we see, where before was a dead sea of innumerable facts, new vital laws arising and guiding principles.
NOTES.
1. P. 247. Cytom'orphosis was first used in the Middleton Goldsmith Lecture for 1901, entitled " The Embryological Basis of Pathology," Science, XIII, 481.
2. P. 256. Perhaps all or some of the salivary glands are entodermal. The submaxillary gland belongs among the organs, when it is a single large compound gland with a Bartholini's duct. When the submaxillary is represented by a group of small glands, they belong with the other simple buccal glands.
The position of the mammary gland must remain uncertain, until we can decide whether it is merely a group of glands, or morphologically a true compound gland. The significance of its peculiar development is still unsettled.
The hypophysis will perhaps, with more accurate study, be found to be an anastomosing gland with a sinusoidal circulation.
Charles-Sedgwick Minot 263
3. P. 258. The morphological characteristics of the structural (or histological) unit have been pointed out by Mall, so that the brief inadequate definition seems sufficient for the occasion.
4. P. 252. The account of the formation of sinusoids is somewhat schematic. We now know that the intercrescence of the vessels and parenchyma offers variations especially in its mode of beginning.
5. P. 259. Huntington's Anatomy of the Peritonseum, etc. (1903), is written entirely from the genetic and comparative standpoint. This excellent work, however, is not a general text-book, and in no sense belongs in the class of manuals criticized in the text. Even Huntington's account of the liver seems to me not to take sufficient advantage of our morphological knowledge, especially as regards the primary connection of the liver with the diaphragm and also as regards the sinusoidal circulation.
STUDIES OF THE DEVELOPMENT OF THE HUMAN" SKELETON.
(a). The Development of the Lumbar, Sacral and Coccygeal Vertebra.
(b). The Curves and the Proportionate Regional Lengths of the Spinal Column during the First Three Months of Embryonic Development.
(c). The Development of the Skeleton of the Posterior Limb.
BY CHARLES R. BARDEEN.
Professor of Anatoviy, The University of Wisconsin. With 13 Plates.
The following studies on skeletal development are based upon embryos belonging to the collection of Prof. Mall, at the Johns Hopkins University, Baltimore. I am greatly indebted to Prof. Mall for their use.
A.
THE DEVELOPMENT OF THE LUMBAR, SACRAL AND COCCYGEAL
VERTEBRA.
Eecently I have given an account of the development of the thoracic vertebrge in man (This Journal, Vol. IV, No. 'I, pp. 163-175). In the present paper it is my purpose to describe the special features which characterize the differentiation of the more distal vertebrae.
During the early stages of vertebral development the skeletal apparatus of the various spinal segments is strikingly similar. This is shown in Fig. 1, Plate I, which illustrates the spinal column of Embryo II, length 7 mm. Yet even during the blastemal stage some regional differentiation becomes visible. The costal processes of the thoracic vertebrae, for instance, develop much more freely than those of other regions. It is, however, during the chondrogenous period that the chief regional features appear.
To what extent morphological similarity in the sclerotomes and scleromeres indicates equal formative potentiality experiment alone can deter Ameeican Journal of Anatomy. — Vol. IV, 21
266 Studies of the Development of the Pluman Skeleton
mine. While it is unlikely that experimental studies of the required nature can ever be made on mammalian embryos it is quite possible that they may on embryos of some of the lower vertebrates. From the evidence at hand it seems probable, however, that the primitive vertebrse are to a considerable extent potentially equivalent and that their subsequent development depends upon the demands of their regional environment. The strongest arguments in favor of this view come from a study of variation in the adult. It is well known that at the regional boundaries vertebral variation is frequent. Thus the 7th vertebra often carries a short "cervical" rib (Gruber, 6g), and rarely it has two cervical ribs which run to the sternum (Bolk, oi). On the other hand the 8th vertebra, usually the first thoracic, may assume all the characteristics of a cervical vertebra (Leboucq, 98, Low, 01).
At the thoracico-lumbar margin variation is more frequent than at the cervico-thoracic. Thus out of 1059 instances described, statistically in the literature I found, 1904, that the 19th vertebra, commonly the last thoracic, had no free ribs and was hence of the lumbar type in 30 instances, 2.8%, and that on the other hand the 20th vertebra, commonly the first lumbar, had free costal processes in 23 instances, 2.2%. Cases have also been reported where the 21st vertebra, usually the 2d lumbar, has carried free ribs (Rosenberg, 99). Variation takes place in the articular processes as well as in the costal elements of the vertebra; at the thoracico-lumbar border (Topinard, 77).
Variation of the lumbo-sacral boundary is likewise frequent. Thus out of the 1059 instances above mentioned in 28 instances, 2.7%, the 24th vertebra, commonly the 5th lumbar, was the first sacral and in 47 instances, 4.4%, the 25th vertebra was of the lumbar type. The 25th vertebra may exhibit one of many transitions from the sacral to the lumbar type. This subject has been well treated by Paterson, 93. Papillault, 00, has contributed an interesting paper on lumbar variations and Cunningham, 89, on the proportion of bone and cartilage in the lumbar region.
At the sacro-coccygeal border variation is even more frequent than in the regions more anterior. Paterson, 93, found diminution in the number of sacral vertebrse in 2.62%, and increase in their number in 35.46% of the 265 sacra he examined; and Bianchi, 95, in 17.5% of the female, 23.3% of the male, and 21.23% of the total number (146) of sacra examined. In this count he excluded sacra in which compensation for lumbo-sacral alterations was to be seen. Bianchi thinks that the 1st coccygeal vertebra belongs properly to the sacrum. In the 1059 instances mentioned above I find that the 30th vertebra, usually the 1st coccygeal.
Charles K. Bardeen 267
was reported sacral in natiire in 91 instances, 8.6%, and the 29th, commonly the last sacral, coccygeal in 27 instances, 2.5%. It is possible that variations of this nature were sometimes overlooked by those making up the tables from which the above data were obtained.
Variation other than border variation has been reported most frequently in the cervical region. Eibs have been found not only on the 7th and 6th vertebras but also on those more anterior (Szawlowski, oi).
It seems fair, however, to assume that the primitive vertebrae become differentiated according to the demands of their environment. Thus the factors commonly exerted on the 8th to 19th costo-vertebral fundaments causing them to develop into thoracic vertebrae with free ribs, may be so exerted as to call into similar development the 7th to 18th, the 7th to 19th (20th), the 8th to the 18th, the 8th to the 20th (21st), or the 9th to the 19th (20th). While the thorax may be segmentally extended or reduced at either end, extended at both ends, or extended at one end and reduced at the other, a simultaneous reduction at both ends has not been reported (Eosenberg, 99).
Differentiation in the post- thoracic region depends apparently in the main upon the position of the posterior limb (Bardeen, 00, Ancel and Sencert, 02). When the developing ilium becomes attached to the costal processes of the 25th, 26th (and 27th) vertebrae the conditions of the lumbar, sacral and coccygeal regions are commonly normal. But the developing ilium may become attached further anterior than usual, either directly to the costal process of the 24th vertebra or so far forward that a close ligamentous union is established with it. In such instances the 12th rib is usually either very rudimentary or absent and often the 29th vertebra is of the coccygeal type. In rare instances the thorax may at the same time advance a segment into the cervical region. On the other hand the developing ilium may take a position more posterior than usual, leaving the 25th vertebra either free to develop into the lumbar type or but incompletely united to the sacrum (Paterson, 93). When this occurs the 20th vertebra is very apt to have ribs developed in connection with it and the 30th vertebra usually becomes an integral part of the sacrum.
The coccygeal vertebra, with the exception of the first, which is more directly than the others subjected to the differentiating influences of the developing limb, are relatively more rudimentary in the adult than in the embryo.
Eosenberg, 76, advanced the opinion that the ilium is attached more distally in the embryo than in the adult. I have recently, 1904, shown that this is not the case. On the contrary, as might have been inferred
268 Studies of the Development of the Human Skeleton
from the distribution of the nerves to the posterior limb, the ilium is differentiated in a region anterior to the site of its permanent attachment and the differential activities which it stimulates in the sacral vertebrae are exerted first on the more anterior of these vertebrae.
The two limbs do not always call forth a similar response on each side of the body. Thus Paterson, 93, found asymmetry of the sacrum in 8.3% of the instances he studied.
Assuming the specific differentiation in the lumbar, sacral and coccygeal regions of the spinal column represents a response to stimuli arising in part from the developing limb, we may turn to a consideration of the differentiation thus brought about in each of these regions. Attention will here be directed chiefly to the more salient differences between development in the distal half of the vertebral column and that recently described for the thoracic region.
LUMBAR VERTEBRA.
Eosenberg, 76, seems to have been the first to take up a detailed study of the early development of the lumbar vertebrae in man. He described the costal rudiment of these vertebrae and found in several embryos that this rudiment of the 20th vertebra had given rise to a cartilagenous 13th rib. A careful study of a large number of human embryos has led me, however, to the conclusion (1904) that a 13th rib is no more frequent in the embryo than in the adult and that in the series studied by Eosenberg it must have been unusually frequent. Holl, 82, found no 13th rib in the embryos which he examined. He also came to the conclusion that the transverse processes of the lumbar vertebrae do not represent ribs. Most investigators rightly disagree Avith him on this point.
The development of the external form of the lumbar vertebras in a series of embryos belonging to the Mall collection is shown in Figs. 1-13, Plates I-V.
The bodies of the lumbar vertebrae during the earlier periods of differentiation are essentially like those of the thoracic vertebrae. In embryos over 12 mm. long, however, the former become progressively thinner, broader and longer than the latter. The intervertebral disks and the enveloping ligamentous tissue are similar in both regions. •In the thoracic region the canal of the chorda dorsalis lies nearer the ventral surface of the vertebral column than it does in the lumbo-sacral region. The marked alterations in the curvature of the spinal column which occur during embryonic development seem especially associated with changes in the intervertebral disks.
Charles E. Bardeen 269
The neiiro-cosial processes of the lumbar vertebra are also at first similar in form to those of the thoracic vertebrae. This is the case in Embryo II, length 7 mm.. Kg. 1, Plate I ; CLXIII, length 9 mm., Fig. . 2, Plate II; and CIX, le^igth 11 mm., Figs. 3 and 4, Plate II.
Marked differences in the costal processes are to be seen when chondrofication begins. Thns while the costal process of the 12th thoracic vertebra has early a separate center of chondrofication (Embryo CLXXV, length IS mm., Fig. 14, Plate VI and Embryo CXLIV, length IJf mm.. Fig. 5, Plate III), the processes of the lumbar vertebrae remain for a considerable period dense masses of mesenchyme (Embryo CLXXV, length 13 mm.. Figs. 15 and 16, Plate A^I, and Embryo CCXVI, length 11 mm.. Figs. 18 and 19, Plate VI). Finally, however, they undergo chondrofication at the base (Embryo XXII, length 20 mm., Figs. 21 and 22). I have been unable to determine whether this chondrofication always takes place from a separate center, as it certainly often does, or sometimes represents merely an extension into the costal mesenchyme of cartilage from the -transverse process. I incline to the former view.
Sometimes the costal element of the 1st lumbar vertebra may remain for a considerable period separate from the cartilage of the transverse process. This is true of the right side (left in the figure) of Embryo XLV, length 28 mm.. Fig. 24. But usually at an early period the costal and transverse processes become intimately fused (Embryo XXII, length 20 mm.. Fig. 21; XLV, length 28 mm., Fig. 24, right side of figure; and Fig. 25 ; Embryo LXXXIV, length 50 mm.. Figs. 27 and 28) . The " transverse " process of the adult lumbar vertebra represents in the main an ossification of a membranous, not cartilagenous, extension of the fused costal element (C. Pr., Fig. 28).
At first the neural processes of the lumbar vertebrae are essentially like those of the thoracic (Embryo CXLIV, length IJ/. mm.. Fig. 5, Plate III). Union of the pedicles with the cartilage of the body takes place and the laminae extend out dorsally in a similar manner in each. It is in the transverse and articular processes that the chief characteristic differentiation takes place.
The lumbar transverse processes are broader and much shorter than the thoracic. At an early period, as mentioned above, they become intimately united to the costal processes. In the dense mesenchyme between the region of the transverse process and the costal element there is commonly developed no loose vascular area such as serves to separate the neck of the developing rib from the transverse process in the thoracic region. The occasional appearance of a foramen in a transverse process of a lumbar vertebra has led to the supposition that they may occur
370 Studies of the Development of the Human Skeleton
regularly in the embryo (Szawlowski, 02, Dwight, 02). The differences between the transverse processes of the 12th thoracic and the first two •lumbar vertebras in several embryos are shown in Plates VI and VII, Figs. 14 to 28.
The articular processes in the lumbar, as in the thoracic, region are at first flat plates connected by membranous tissue," Fig. 5, Plate III. But in the lumbar region the superior articular process develops faster than the inferior so that each superior process comes partly to enfold the inferior process of the vertebra next anterior. These conditions may be readily followed in Figs. 9, 12 and 13, Plates IV and V, and in Figs. 20-28, Plates VI and VII. The mammillary and accessory processes of the adult lumbar vertebra probably represent an ossification of muscle tendons attached to the transverse and articular processes.
During the development of the vertebrae in embryos from 30 to 50 mm. in length alterations preliminary to ossification, similar to those in the thoracic, occur in the lumbar vertebra. ISTo actual ossification occurs in any of the centers in the latter in embryos less than 5 cm. long in Prof. Mall's collection. It begins in the bodies of the more anterior of the lumbar vertebrae in embryos between 5 and 7 cm. long, and in those 8 cm. long it has usually extended to the more distal. Meanwhile, ossification of the neural processes has extended from the thoracic into the lumbar region and soon may be seen throughout the latter. See Bade, 00.
SACRAL VERTEBRA.
Although much has been written about the ossification of the sacral vertebra comparatively little attention has been devoted to their early differentiation. Eosenberg, 76, contributed several important facts, ' although the general conclusions which he drew concerning the transformation of lumbar into sacral, and sacral into coccygeal vertebrEe are unw^arranted. Holl, 82, studied more especially the relation of the ilium to the sacrum in adults and embryos and added materially to the knowledge of the sacro-iliac articulation. Petersen, 93, has given an incomplete description of the sacrum in several early human embryos, and Hagen, 00, of one 17 mm. long.
Figs. 1 to 13, Plates I to V, show the general external form of the sacral vertebrae in embryos of the Mall collection. In Embryo II, length 7 mm.. Fig. 1; CLXIII, length 9 mm.. Fig. 2; and CIX, length 11 mm., Figs. 3 and 4, the sacral appear to resemble the lumbar in all essential particulars, although there is a progressive decrease in size from the midlumbar region distally. No line of demarcation can be drawn in these embryos between the sacral and lumbar vcrtebrse on the one side and tlie sacral and coccygeal on the other.
Charles R. Bardeeu 271
Soon after the stage shown in Figs. 3 and 4 the iliac blastema approaches more closely the vertebral column, usually in the region opposite the costal processes of the 25th and 26th vertebrse. These, then, are stimulated to more active growth and extend in their turn out toward the ilium. The costal processes of the 27th, 28th and 29th vertebrse are likewise stimulated into more active growth. Lateral to the ventral branches of the spinal nerves the tissue derived from the costal elements of these five vertebra3 becomes fused into a continuous mass of condensed tissue (Fig. 37, Plate IX; and Figs. 5 and 6, Plate III). Against the anterior and better developed portion of this the iliac blastema comes to rest (Figs. 5 and 37). From the time of the fusion of the costal elements of the sacral vertebra into a continuous lateral mass of tissue these vertebrge may be distinguished from the lumbar and coccygeal. A^ariation in the vertebrae entering into the sacrum occurs in the embryo as in the adult (Bardeen, 04).
At the period when the iliac blastema comes into contact with the costal mass of the sacrum centers of chondrofication have appeared in the bodies of the sacral vertebras. The bodies, compared with the intervertebral disks, are progressively smaller from the first to the fifth CEmbryo CXLIY, Jenf]tli 14 mm.. Fig. 6). Otherwise they present no characteristics of special note. In older embryos this difference becomes less and less marked.
The neuro-costal processes present features of more specific interest. In Embryo CXLIV, length IJf mm., centers of chondrofication may be observed in the neural processes of the first two sacral vertebras. They are not yet united to the bodies of the vertebrae and are simple in form. Xo cartilage has as yet appeared in the neural processes of the other vertebra. In somewhat older embryos, CCXVI, length 17 mm.. Fig. 38, and CLXXXVIII, length 17 mm.. Fig. 39, the neural processes of all the sacral vertebrae have become chondrofied and distinct. Separate centers of chondrofication may be seen in each of the costal elements. At a slightly later stage, Embryo XXII, length 20 mm., Eig. 10, Plate IV, the extremities of the costal elements of the first three sacral vertebrae have fused with one another and have thus given rise to a cartilaginous auricular surface, and each has fused with the neural arch of the vertebra to which it belongs. The costal elements of the 4th and 5th sacral vertebrae are likewise fused to their corresponding neural arches and all of the sacral neural arches are fused to their respective vertebrae.
Cross-sections illustrate well the relations of the neural and costal processes to the vertebrae. Embryo CIX, length 11 mm.. Fig. 29, Plate VIII, shows an early blastemal stage in which the sacral vertebras resem
272 Studies of the Development of the Human Skeleton
ble the thoracic. Figs. 30, 31 and 32 represent cross-sections through tlie 1st, 2d and 3d sacral vertebrae of Embryo X, length 20 mm. The neural and costal processes in this embryo show cartilagenous centers, but these are fused neither with one another nor with the vertebral body. Embryo CCXXVI, length 25 mm., Figs. 33 and 34, shows fusion of neural and costal processes with the body. The costal processes have by this period given rise to a continuous lateral cartilagenous mass, a portion of which is represented in Fig. 40. This shows an oblique section through the 3d and 4th sacral vertebrse of Embryo LXXXVI, length 30 mm. This cartilagenous lateral mass may likewise be seen in the sacra of Embryo CXLV, length S3 mm.. Figs. 11 and 12, and LXXXIV, length 50 mm.. Fig. 13.
From the primitive neural cartilages there develop pediclar, transverse, articular and laminar processes. The pediclar and transverse processes become intimately fused with the costal element as described above. In none of the embryos examined was there seen a separation of costal from transverse process marked by blood-vessels, such as one might perhaps expect to find because of the occasional appearance in the adult of transverse foramina in the lateral processes of the sacral vertebrae (Szawlowski, 02),
The articular processes in the older embryos retain a more primitive condition than do those of the lumbar and thoracic regions. Figs. 33, 34, 35 and 36 show cross-sections through the articulations of the neural processes.
The laminar processes of each side are still separated by a considerable interval in embryos of 50 mm., although at this period the lumbar region is nearly enclosed. Compare Figs. 28 and 36.
Changes in the cartilages preliminary to ossification occur both in the bodies and in the neural processes of the sacral vertebras at a period quickly following their appearance in the lumbar region. Thus iji Embryo LXXlX, length 33 mm., changes of this nature may be followed as far as the 5th sacral vertebra. It is well known, however, that actual ossification in the more distal sacral vertebrae takes place considerably later than in the thoracico-lumbar region. The primary centers of ossification correspond with the centers of chondrofication except that there is a single center in place of two centers for each body, and one center instead of two for each neuro-costal processes of the two more distal sacral vertebrae. Posth, 97, has recently contributed a valuable paper on the subject of sacral ossification.
Charles K. Bardeen 273
COCCYGEAL VERTEBRA.
Since the valuable contributions of Fol, 85, who described 38 vertebrae in the early human embryo, considerable attention has been devoted to the development of the coccygeal vertebrae, especially from the point of view of the number of vertebrse in embryos. The literature on the subject has been summed up by Harrison, 01, and more recently by linger and Brugsch, 03. Tlic later stages in the development of the coccyx have been described by Steinbach, 89, who studied a large number of spinal columns of foetuses, infants and adults. In a recent paper, 1904, I have given a summary of the number of coccygeal vertebrae found in various embryos and of the number of hremal processes found in the embryos belonging to the collection of Prof. Mall.
Without attempting here to enter into a detailed account of the conditions found in these various embryos we shall pass at once to a consideration of the more characteristic features of coccygeal development. The differentiation of the coccj'geal sclerotomes begins at about the end of the fourth week. Embryo II, length 7 mm., Pig, 1, Plate I. As a rule at least six or seven membranous vertebrae are developed. The highest relative differentiation of the coccygeal vertebrae occurs in the fifth and sixth weeks. At this time dorsal processes connected by interdorsal membranes extend as far as the 4th and 5th vertebra. Figs. 3 and 4, Plate III, Fig. 41, Plate X. No distinct costal processes are, as a rule, developed on any except the first coccygeal vertebra, but at the height of development most of these vertebras have distinct haemal processes, first described by Harrison, 01. These processes may also be seen on the more distal sacral vertebrae. Fig. 41, Plate X. They usually disappear before the embryo has reached a length of 20 mm., but the coccyx described by Szawlowski, 02, suggests that occasionally they are retained until adult life.
Usually the bodies of the first five coccygeal vertebrae become chondrofied. The chondrofication of the more distal of these vertebrae is, as pointed out by Rosenberg, 76, often very irregular. There may be separate bilateral areas of cartilage or the two areas may be connected merely anterior to the chorda dorsalis. The bodies of successive vertebrse may be irregularly fused.
As a rule the neural processes of the first coccygeal vertebra alone become chondrofied and fused to the vertebral body. The others, as well as the connecting interdorsal membranes, disappear.
The cartilagenous coccygeal vertebrae are thus relatively less developed than the membranous. It is probable that the osseous are less developed than the cartilagenous. Tluis although Steinbach, 89, has made a strong
374 Studies of the Development of the Human Skeleton
plea for the presence of 5 vertebrae in the adult coccyx, the more commonly accepted number of four seems to be a truer estimate of the definite number of bones usually found present.
The bend of the coccyx which takes place during the third month is an interesting phenomenon. It seems to be associated with the development of pelvic structures.
SUMMARY.
In the earlier stages of development the lumbar, sacral and coccygeal vertebrae resemble the thoracic. The blastemal vertebrae arise each from the contiguous halves of two original segments of the axial mesenchyme. Each vertebra exhibits a body from which neural and costal processes arise. The neural processes are connected by " interdorsal " membranes.
As the blastemal vertebrse become converted into cartilage specific diiferentiation becomes more and more manifest. The cartilagenous vertebral bodies and the intervertebral disks are all formed in a similar manner and except for size manifest comparatively slight differences in form. The more distal coccygeal vertebrae are, however, irregular. But the chief specific differentiation is seen in the costal and neural processes.
In the blastemal neural processes of the thoracic vertebras cartilagenous plates arise from which spring pediclar, transverse, articular and laminar processes.
In the lumbar vertebrae similar processes arise from the neural cartilages. The pediclar processes resemble the thoracic but are thicker; the transverse processes are shorter, much thicker at the base and remain bound up with the costal processes; the superior articular processes develop in such a way as to enfold the inferior ; the laminar processes are broad, grow more directly backward than do the thoracic, and on meeting their fellows in the mid-dorsal line fuse and give rise to the typical lumbar spines. The mammillary and accessory processes are developed in connection with the dorsal musculature.
In the sacral vertebrae the neural cartilages give rise to very thick pediclar processes; to articular processes the most anterior of which develop like the lumbar, while the others long maintain embryonic characteristics; to transverse processes which in development are bound up with the costal processes; and to laminar processes which are very slow to develop and of which the last fail to extend far beyond the articular processes.
In the coccygeal vertebrae the neural processes of the first, and rarely
Charles E. Bardeen 275
the second, alone give rise to cartilagenous plates. From these only pediclar and incomplete articnlar and transverse processes* arise. The cornua of the adult coccyx represent fairly well the form of the early nenral semi-arches. The transverse processes develop in close connection with the costal processes.
In the thoracic vertebrae cartilagenous ribs develop from separate centers in the blastemal costal processes.
In the lumbar vertebrse separate cartilagenous centers probably always arise in these processes, but they are developed later than those of the thoracic vertebrse and quickly become fused with the cartilage of the transverse processes. The transverse processes of the adult lumbar vertebrse represent at the base a fusion of embryonic cartilagenous costal and transverse processes, but in the blade an ossification of membranous costal processes.
In the sacral vertebrse separate cartilagenous costal centers are developed but they soon become fused at the base with the transverse processes of the neural plates. Laterally by fusion of their extremities the costal processes give rise to an auricular plate for articulation with the ilium.
In the coccygeal vertebrse the costal processes of the first become fused with the transverse processes and develop into the transverse processes of the adult coccyx. I have been unable definitely to determine whether a separate costal cartilage is developed in these processes or cartilage extends into them from the neural processes. The costal processes of the other coccygeal vertebrse have merely a very transitory blastemal existence.
For a brief period the more distal sacral and the coccygeal vertebrse have membranous hsemal processes.
Centers of ossification correspond in general with centers of chondrofication, but, as in the case of the vertebral bodies and the more distal sacral neuro-costal processes, a single center of ossification may represent two centers of chondrofication.
B.
THE CURVES AND THE PROPORTIONATE REGIONAL LENGTHS OF
THE SPINAL COLUMN DURING THE FIRST THREE MONTHS
OF EMBRYONIC DEVELOPMENT.
In 1879 Aeby contributed an imoprtant paper dealing with the lengtli of the various regions of the spinal column at different ages, the heigh. t of the constituent vertebrse and the thickness of the intervertebral disks
276 Studies of tlic Development of tlie Human Skeleton
in man. He showed that in young embryos the cervical region is relatively longer than the lumbar region but that as growth proceeds there is a constant proportional increase in length of the latter over the former. Taking the cervical region as 100, for instance, he found that in embryos below 10 mm. in length the lumbar region equals 69, while in the adult it is equivalent to 150. Thus, too, while from infancy to maturity the spinal column increases three and one-half times in length and the thoracic region at about the same relative ratio, the lumbar region increases four times in length and the cervical but three. Other investigators, including Ballantyne, 92, and Moser, 89, have in general confirmed these results. Of those who have studied the proportional length of the various regions in the adult Eavenel, 77, and Tenchini, 94, have made noteworthy contributions.
The post-natal lengthening of the lumbar region is associated with those changes in the lumbo-sacral curve which accompany the assumption of an erect posture during early childhood. Do similar alterations in relative regional length accompany the straightening of the spinal column which takes place during the first three months of embryonic development?
In Fig. 44, Plate X, I have represented by curved lines the vertebral columns of several embryos of this period and an adult column. The cervical, lumbar and coccygeal regions are represented by heavy, the thoracic and sacral regions by light lines. The 5th, 6th and 7th thoracic vertebrae are made to coincide in each instance.
The anterior half of the spinal column is considerably curved in Embryo II, length 7 mm. It gradually becomes straightened in successively older embryos until in Embryo CLXXXIV, length 50 mm., it is nearly straight. The subsequent anterior convexity in the adult is associated with the assumption of an upright position of the head.
It is, however, in the posterior half of the spinal column that the chief alterations in spinal curvature are to be noted. In Embryo II, length 7 mm., the ventral surface of the sacral region faces the mid-thoracic region; in Embryo CIX, length 11 mm., the anterior end of the vertebral column; in Embr3^o CLXXXIV, length 50 mm., almost directly ventrally; and in the adult, in a posterior direction.
The relative lengths of the various regions of the spinal column during the first three months of development may be gathered from the following table, which is based in part upon data obtained from embryos belonging to the Mall collection and in part upon those of the Born and His collections studied by Aeby.
Charles E. Bardeen
277
TABLE A.
The lengths of the various regions of the spinal columns of embryos OF the second and third months, and the proportional length of the
THORACIC compared WITH THE OTHER REGIONS.
Embrj'os.
Regions of the spinal column.
«
o o
Length in mm.
Cervical.
Thoracic.
Lumbar.
Sacral.
Coccygeal
Designation.
fa
is
2
.2 .
Is
J-S
•=3 a
p .
OS3.2
fa
.9
og.2
5 a
o .
og.2
II.
Mall
7
60.6
3.3
1.2
36.4
27.3
CCXXI.
K
13(1)
2
63.5
3.2
1.3
46.1
1.25
39.1
1.0
31.2
1 (Aeby).
His.
10
2.95
76.6
3.85
1.75
45.5
1.95
50. 6 C^)
CIX.
Mall.
11
2.7
67.5
4
2
.50.0
1.7
413.5
1.3
32.5
CXLIV.
II
14
2.3
62.2
3.7
1.7
46.0
1.34
36.2
1.1
29.8
XLIII.
II
16
2.9
61.9
4.34
1.9
43.7
1.55
35.7
1.41
32.5
2 (Aeby).
His.
10
3
65.2
4.6
2.25
48.9
1 88
40.9(2)
3 (Aeby).
II
16
3
64.5
4.65
2.25
48.2
2.65
57.0(2)
XXII.,
Mall.
20
5 5
3
54 5
3.0
36.4
1
35
4 (Aeby).
His.
21.5
3.9
61.9
6.3
3.1
49.2
3.4
53.9rf2)
CVIII.
Mall.
22
4.34
61.9
7.0
3.5
50.0
2.8
40
1.3
16.1
CXLV.
u
33
5.1
59.5
8.55
4
46.8
3.5
35.6
1.75
30
CCXXVII.
30
5.4
60.0
9.0
4
44.4
3
33.3
1.38
15.3
5 (Aeby).
Born.
6.0
54.5
11
5.2
47.3
xcv.
Mall.
46
8.25
59.0
14
7.25
51.8
5.5
39.3
3.75
36.8
CLXXXIV.
11
50
8
61.1
13
6.35
48.8
4.65
35.8
3.65
30.4
6 (Aeby).
Born.
10
58.8
17
8.5
50.0
9.5
55.8(5)
••
1. This is the measurement recorded before the embryo was sectioned. The embryo was cut sagittally. The length of the sections in the median line is 7.5 mm. The general development corresponds with that of an embryo of this length.
2. These figures represent the length of the pelvic portion of the spinal column.
This table discloses considerable individual variation. The length of the cervical region is about 60% of that of the thoracic. In Embryos CIX, 1 and 2, this ratio is much exceeded. The measurements for CIX are calculated from obliquely transverse sections and hence are subject to some error. The data concerning the measurements for 1 and 2 are not given by Aeby.
The lumbar region, at first less than 40% in length of the thoracic, in most embryos approximates 50%. The length of the sacral region varies from 33 to 42.5% of the thoracic. The coccygeal region, with a nearly constantly diminishing comparative length, shows marked variations.
There is no good evidence that the straightening of the spinal column is accompanied by a marked increase in relative length of the lumbar region after the early stages in Embryos II and CIX.
27S Studies of the Development of tlic Human Skeleton
A comparison of the spinal columns of embryos of the second and third months with those of older embryos and of children shows that it is during the latter half of foetal life and early childhood that the chief relative lengthening of the lumbar region takes place.
i\.ccording to Aeby the average length of the cervical, thoracic and lumbar regions in the new-born is respectively 45.1, 83.9 and 47.5 mm. This makes the length of the cervical region 53.5% and that of the lumbar region 5G% of that of the thoracic. Corresponding figures from Ballantyne, 92, for full-term foetuses are: cervical, 33.6 mm. (42.8%) ; thoracic, 78.4 mm. (100%); lumbar, 42.8 mm. (54.3%); and sacrococcygeal, 39.8 mm. (50.8%). Thus Ballantyne finds a greater proportional reduction of the cervical region.
The conditions in the adult, as given by various investigators, are as follows :
TABLE B.
Pbopoktional lengths of the various
REGIONS OF ADULT
SPINAL
COLUMNS.
r
erase lenyth of ■gions in ram.
Ratio of other regions to. the thoracic as 100.
_.
6
t^
1 "^
__.
^
,"3
Investigator and date.
Sex and S.ze.
133
a
2
o
jd H
280
si S
£ be a >,
as a
01 o
o
a
a ®
47.5
1
o >>
03 a coa
a
Ravenel, 1877.
Male.
182
65.0'
Female.
120
260
178
46.1
68.5
Aeby, 1879.
Male.
139.9
273.4
184.1
47.5
67.3
Female.
122.9
265.8
190.3
46.2
71.6
Tenchini.
Short.
98
222
125
151
44.1
56.3
68
Medium.
100
240
137
158
41.7
57.1
65 8
!S
Tall.
104
240
134
168
43.3
55.8
61
Dwight, 1894.
Mule.
133
287
19.9
46.3
69 . 3
Female.
121
265
18.7
45.7
70.6
The chief point of interest in this table is the difference between the results found by the German and American investigators and those of the Italian. Apparently the Italians have proportionately shorter cervical and lumbar regions than the Americans and Germans, but it is possible that different ways of measuring were used. It is a subject worthy of further investigation.
Both Tenchini and Ancel and Sencert, 02, have treated of variations in measured length of individual vertebrae associated with numerical vertebral variation.
Charles \l. Bnrdccii 279
C.
THE DEVELOPMENT OF THE SKELETON OF THE POSTERIOR LIMB.
One of the most studied subjects in morphology has been the development of the vertebrate limbs. Fortunately critical summaries of its immense literature have recently been given by several keen investigators, among whom may be mentioned Wiedersheim, 92, Mollier, 93, 95, 97, Gegenbaur, 98, 01, Klaatsch, 00, Eabl, 01, Fiirbringcr, 02, Kuge, 02, and Braus, 04. Therefore no attempt will here be made to review previous Avork except in so far as it deals directly with the development of the human limb.
During the third week of embryonic life the limb-buds become filled with a vascular mesenchyme (Bardeen and Lewis, 01, p. 17, Figs. 18 and 19). The source of this tissue is uncertain. In part it may come from the primitive body-segments, but it seems probable that in the main it comes from the parietal layer of the unsegmented mesoderm.
During the fourth week the mesenchyme increases in amount and the limb-bud begins to protrude further from the body-wall. Observed structural differentiation does not, however, begin until the early part of the fifth week, at the time when the lumbo-sacral spinal nerves are beginning to form a plexus. At this period the tissue at the center of the base of the limb becomes greatly condensed. Embryo CLXIII, length 9 mm.. Fig. 45, Plate XI. The boundaries of the mass are not perfectly definite, but a wax-plate reconstruction based upon drawings made as definite as possible gives rise to the structure shown in Fig. 2, Plate II. The relations of this tissue mass to other structures are shown in Plate II, Fig. B, and Plate III, Fig. C, of the article by Bardeen and Lewis, 01. The condensation represents the acetabulum and the proximal end of the femur. This is indicated by its relations to the nerve plexus.
Once begun skeletal differentiation proceeds rapidly. In Embryo CIX, length 11 mm.. Figs. 3 and 4, it may be seen that from the original center of skeletal formation the condensation of tissue has extended both distally and proximally, but much more rapidly in the former than in the latter direction. Distally the sclero-blastema shows femur, tibia, fibula, and a foot-plate; proximally, an iliac, a public and an ischial process. A series of sections through the skeletal mass (Figs. 46 to 53) shows that in the femur, tibia and fibula chondrofication has begun. At the centers of the blastema of the ilium, ischium and pubis a still earlier stage of chondrofication has made its appearance. The leg of this embryo, therefore, represents a stage of transition from the blastemal to the chondrogenous stage of development. Fig. 55, Plate XII, shows a longitudinal
280 Studies of the Development of the Hainan Skeleton
section throngh the leg of Embryo CLXXV, length IS mm. The development is slightly more advanced than in Embryo CIX.
The further general development of the skeleton of the limb may be followed in Figs. 8 to 13. For the sake of convenience the development of the several parts of the skeleton will be taken up in turn as follows: (a) pelvis; (b) femur, hip-joint, tibia and fibula, and knee-joint; (c) ankle and foot.
A. PELVIS.
Petersen, 93, has given a good account of the early development of the human pelvis. His Avork was based upon embryos belonging to the His collection. In embryos Eu, length 9.1 mm., Ko, length 10.2 m.m., and IST, length 9.1 mm., the formation of the lumbo-sacral plexus has begun and there is a condensation at the center of the limb-bud. The conditions here resemble those in Embryo CLXIII, length 9 mm., Fig. 2, described above. Petersen believed that the condensation of tissue in embryos Eu and Ko represents the germinal area for the muscles and skeleton of the lower extremity while that of IST shows a further differentiation of the diaphysis of the femur. The last ends anteriorly in a small undifferentiated cell-mass but there is nothing further to indicate the future pelvis. Yet, as I have mentioned above, the relations of this cell-mass to the nerves arising from the plexus indicates that it is the fundament of the future pelvis. The nerves pass about it as they do later about the acetabulum. In Embryo S^, length 12.6 mm., Petersen found what he considers the first traces of a definite pelvic fundament. This embryo is evidently of about the same stage of development as CIX, length 11 mm.. Figs. 3 and 4 and 46 to 53. But CIX is slightly more advanced and shows early stages of chondrofication not seen in S^. The pelvis of S^ has a slightly more anterior position and the iliac blastema extends rather toward the 24th than the 25th vertebra (Fig. 1, Plate I, of Petersen's article) .
The pelvic scleroblastema of embryos of the stage found in CIX undergoes a rapid development. Its iliac portion extends in a dorsal direction toward the vertebrae which are to give it support. The costal processes of the latter at the same time become fused into an auricular plate. With this the iliac scleroblastema comes into close approximation. Figs. 5 and 6, Plate III, although for some time separated by a narrow band of tissue staining less densely than the blastemal. Fig. 37.
Anteriorly the iliac blastema extends toward the abdominal musculature, to which it finally serves to give attachment.
While the blastemal ilium is thus becoming differentiated the pubic
Charles E. Bardeen 381
and ischial processes of the pelvic blastema extend rapidly forward and ventral to the obturator nerve they become joined by a condensation of the tissue lying between them. Thus the obturator foramen of the blastemal pelvis is completed. Figs. 5 and 6. Between the crest of the ilium and the ventral extremity of the pubis dense tissue is formed to give attachment to the oblique abdominal musculature. This represents the embryonic Poupart's ligament and completes a femoral canal, Figs. 5 and 6.
While the blastemal pelvis is being differentiated the formation of cartilage in the ilium, ischium and pubis extends rapidly from the centers indicated in Embryo CIX. In CXLIV, length IJ^ mm., Figs. 5, 6 and 54, the three cartilages are distinct.
The iliac cartilage is a somewhat flattened rod with anterior and posterior surfaces. Fig. 38. The anterior surface of the iliac cartilage at first faces slightly laterally as well as anteriorly. Lubsen, 03, in an interesting paper has shown the importance of this from the standpoint of mammalian phylogeny. He considers a flat plate with median and lateral surfaces to be the probable primitive form of ilium from which the triangular form, on which Flower, 70, laid stress, is derived by a lateral projection serving to divide the lateral surface into an anterior iliac and a posterior gluteal portion. In man and some other mammals the anterior iliac surface, according to Lubsen, comes to be turned medially by a great extension of the lateral projection and a secondary union of the abdominal musculature to this. In man, however, the primitive iliac cartilage is a rounded plate of which the long axis of the cross-section lies nearly at right angles to the median plane of the embryo. On the whole it suggests the prism described by Flower.
The pubic and ischial cartilages when first formed are mere rounded masses of tissue lying in the center of their respective blastemal processes. The acetabulum at this time is composed mainly of blastemal tissue but the iliac and ischial cartilages form a part of its floor. Embryo CXLIV, length 14- mm.. Figs. 5 and 6, Plate III. The pelvis of CR, length 13.6 mm., described by Petersen and pictured in Fig. 2, Plate I, of his article, is of a stage of development similar to that of CXLIV. The cartilages are slightly more advanced in development. The iliac cartilage is broader in an antero-posterior direction and extends to the sacrum. He observed no dense tissue completing the obturator foramen but this tissue is quite plain in the corresponding embryos of the Mall collection, and it is described by Petersen for embryos Wi, length 15.5 mm., and Ob, length 15 mm., which are slightly more advanced than CE.
22
282 Studies of the Development of the II u man Skeleton
While the hnman embryo is growing from 15 to 20 mm. in length, there occnrs a rapid development of the pelvic cartilages. About the head of the femur each gives rise to a plate-like process. The fusion of these processes produces a shallow acetabulum, Figs. 9 and 10, Plate IV. Those from the ilium and ischium are larger than that of the pubis and fuse with one another before the pubic cartilage fuses with them. The proportional areas of the acetabulum to which each pelvic cartilage contributes seem to be essentially the same as those later furnished by the corresponding pelvic bones, % -|- ischium, % — ilium, % pubis. AVhile growing about the hip-joint so as to complete the acetabulum each of the pelvic cartilages has a centrifugal growth within the blastemal pelvis. It is convenient to consider each cartilage in turn.
The iliac cartilage of the stage represented in Embryo CXLIV, Figs. 5 and 6, represents essentially that portion of the ilium which borders the entrance to the true pelvis and which has hence been called the pelvic portion of the ilium. From this cartilage extends dorsally into the sacral area of the blastemal pelvis. Figs. 9 and 10, and there gives rise to the sacral portion of the cartilagenous ilium. At the same time cartilage extends into the blastema which passes anteriorl}^ to give attachment to the abdominal musculature and from this arises the abdominal portion of the cartilagenous ilium. A slight extension of cartilage into the anlage of Ponpart's ligament forms the anterior superior spine, but the blastemal covering of the femoral canal is not converted into cartilage as is the similar covering of the obturator.
While the cartilagenous ilium is being developed the ischial and pubic cartilages extend ventrally into their corresponding blastema. The ischial cartilage rapidly increases in thickness and at the same time gives rise to two processes. One of these, the ischial spine, extends toward the sacrum. This seems to indicate a commencing enclosure by cartilage of the ilio-sciatic notch. The other projects toward the developing hamstring muscles and gives rise to the ischial tuberosity.
The pubis broadens as it extends forwards and beyond the obturator foramen sends down a process which fuses with a longer one extending up from the ischium.
The various stages in the formation of a cartilagenous innominate bone have been followed in detail by Petersen in a series of six embryos from 17.5 to 22 mm. in length. In general what he describes coincides well with the appearances presented in a somewhat more extensive corresponding set of embryos belonging to the Mall collection. The distal position of the ilium, represented in Fig. 12, Plate YII, of Petersen's article, is to be looked upon as an individual variation and not as a
Charles R. Bardeen ■ 283
regular step in the jsrocess of attachment of ilinin to spinal column. This I have previously pointed out (1904). Hagen, oo, has given an account of the pelvis of an embryo of 17.5 mm., wliich corresponds with the description given above.
During the further development of the cartilagenous pelvis the ventral extremities of its two halves, at first widely separated, in embryos of 20 mm. in close proximity, are finally united by a symphysis when the embr3'o reaches a length of 25 mm. In an embryo of this length, CCXXVI, the blastemal tissue of each half is fused in the median line blit the cartilages are separated by % mm., although the width of the pelvis at the rim is only 3 mm. In this embryo the obturator foramen is completely enclosed by cartilage. In embryos of 30 mm. the pubic cartilages are closely approximated in front.
Petersen reconstructed the pelvis of an embryo of 29 mm., Lo^^, and has given an extensive description of it. In essential features it corresponds with the pelvis of Embryo CXLY, length 33 mm.. Figs. 11 and 12. The sacrum of this latter embryo is, however, composed of the 25th 10 29th vertebrse, while Petersen found the 30th vertebra of Lo^ belonging to the sacrum. This variation is common in the adult.
Of the characteristic features common to Lo^ and CXLV may be mentioned the relatively great development of the sacral portion of the ilium, with a large posterior-superior spine, the relatively slight development of the abdominal portion, and the comparatively large part of the pelvic entrance which is bounded by the sacrum. In the adult, according to Engel, the sacrum bounds 26.2% of this. For the new-born female the following figures are given by Fehling: sacrum, 28.9%; ilea, 29.2%; pubes, 42.8% ; for the new-born male, 30.4%, 26.9% and 42.2%. For Loj, the percentages are: 37.0%, 31.7% and 31.3%; for CXLV, 34%, 33% and 33%.
In Loj the rim of the acetabulum is deepened by dense blastemal tissue. In CXLV this has been in part converted into cartilage by extension of processes from the ilium, ischium and pubis. The processes of the ischium and pubis are fused with that of the ilium Init not with one another, so that the cotyloid foramen is well marked.
In both embryos the iliac blades bend more sliarply than in the newborn and resemble in this respect tiie adult. The ischial spines are relatively more developed and project more into the pelvis than do those of the adult.
The pelvis of Lo^ is that of a female ; the pelvis of CXLV that of a male. It is of some interest to determine wliether or not sexual difi'erentiation is apparent. Fehling, 76, showed tliat during foetal life differ
2S-J: Studies of the Develoi)ment of the Human fSkeJcton
ences of this nature, though by no means marked, are none the less to be made out. His conclusions have been confirmed by Veit, 89, Eomiti, 92, Konikow, 94, Thomson, 99, and Merkel, 02. Petersen has made most careful comparisons between the measurements of the pelvis he reconstructed and the structural data furnished by Fehling; The variations due to sex are, however, so slight that they are likely to be obscured in wax reconstructions of early embryos. Allowance must be made for errors of technique and for the difficulty of determining corresponding points between which measurements are to be taken. Thus, for instance, the proportional widths of the entrance to the true pelvis, the pelvic cavity and the pelvic exit I find to be in CXLV as 100 : 75 : 54, while Petersen makes them for Lo^ as 100:74.7:46.1. According to theory the width of the exit should be proportionately less in the male than in the female pelvis. For foetuses of 30 to 34 cm. Fehling gives for females 100 : 88 : 70 ; for males 100 : 87 : 60 ; for new-born females 100 : 84 : 76 ; for new-born males 100 : 82 : 65 ; for adults 100 : 92 : 81. Without the possibility of a direct comparison of the two reconstructed pelves it is therefore scarcely possible to determine accurately to what extent they may show sexual differences. A characteristic on which Merkel, 03, lays especial stress, the more posterior position of the greatest width at the pelvic entrance in the male, does, 1 think, exist in CXLA^ in comparison with Lo^.
These two embryos show that at the beginning of the third month of development the cartilagenous pelvis is well formed. At this time, also ossification begins in the ilium. Preliminary changes in the cartilage may be seen in embryos of 25 mm. in an area corresponding to that in which chondrofication commenced. These changes are further advanced in CXLV, but in this embryo neither deposit of calcium salts nor true ossification has commenced in the ilium although ossification is under way in the clavicle, inferior and superior maxillae, occipital, humerus, radius, ulna, femur, tibia and fibula. Another embryo of the same length, 33 mm., LXXIX, does, however, show a well-marked area of ossification, Fig. 58. In the endochondral region calcium salts are deposited while on each side of this perichondral ossification takes place. In an older embryo, LXXXIV, length 50 mm., this latter process shows well, Fig. 36. It is known that ossification of the ischium and pubis takes place considerably later, that of the ischium beginning in the 4th month and that of the pubis in the 6th to 7th (Bade, 00).
Aside from the ossification of the ilium nothing especially notewortliy seems to take place in the development of the pelvis during the period
Charles R. Bardeen 285
when the embryo is growing from 30 to 50 mm. in length. Fig. 13 shows the form of the pelvis in an embryo of the latter size.
The relations of the pelvis to the sacrum dnring the second and third months of life deserve some attention. I have endeavored to illustrate them in Fig. 44. The curves of the spinal columns of several embryos and an adult arc there shown. A point " a " represents the place where a line joining the centers of the two acetabula would cut the median plane of the embryo. From this point dotted lines are drawn to each extremity of the sacral region and one is projected perpendicularly to a line joining these two extremities. A fourth line from point " a " indicates the direction of the long axis of the femur.
In Embryo II, length 7 mm., the leg skeleton is not differentiated. " a " represents there the approximate position where the pelvic blastema will first become marked, as in Embryo CLXIII, length 9 mm. The perpendicular falls on the body of the 1st sacral vertebra and points toward the mid-thoracic region.
In Embryo CIX, length 11 mm., the perpendicular falls on the 1st sacral vertebra; in CXLIY, length IJ/. mm., about at the junction of the 2d and 3d; in CVIII, length 22 mm., on the 3d; in CXLV, length S3 mm., at the junction of the 2d and 3d; in CLXXXIV, length 50 mm., on the anterior portion of the 3d.
At birth, judging from the figure of Fehling, the perpendicular would strike at about the junction of the 2d and 3d. In the adult the area where it strikes shows much individual variation, but in most of the specimens which I have examined it strikes on the 2d sacral vertebra not far from the junction of this with the 3d. In some specimens it strikes the 3d. The material at my disposal has been chiefly dried specimens from the dissecting room and has been subjected to some warping.
Fig. 44 shows that when first differentiated the pelvis occupies a position anterior to that which it takes when it becomes attached to the vertebral column, but that after this attachment the position of the central area of the acetabulum is altered but slightly with respect to the sacral region of the vertebral column. At the beginning and at the end of the period under consideration it probably occupies a position slightly more anterior than that which it takes during the latter part of the second and first part of the third month of development. The chief alteration of the position of the pelvis with respect to the long axis of the body is due to change in the position of the sacrum in relation to the rest of the spinal column.
Merkel, 02, has contributed an important paper on the growth of the
28G Studies of the Development of the Iluiuaii Skeleton
pelvis and refers to the previous literature on that subject. He shows that the sacrum and the innominate bones exhibit a certain independence in rate of growth.
B. FEMUR AND HIP-JOINT, TIBIA, FIBULA, AND KNEE-JOINT.
The rapid development of the blastemal skeleton of the lower limb has been briefly described above. Soon after the fundament of the femur makes its appearance condensation of tissue marks out the anlage of the tibia and fibula and the skeleton of the foot. This last seems to be at first a somewhat irregular continuous sheet of tissue. It is not clear whether or not the anlage of the tibia and fibula also begins as a continuous tissue sheet which becomes divided, bv' ingrowth of blood-vessels, into tibial and fibular portions. The incomplete development of the interosseous fissure in Embryo CIX, Icngtli 11 mm., Figs. 3 and 4, suggests this. The blastemal anlages of the tibia and fibula are here very incompletely separated.
In Embryo CIX the femoral blastema is continuous at one end with that of the pelvis, at the other with that of the tibia and fibula and that of the last two with the foot-plate.
Within the blastema of the femur, tibia and fibula chondrofication begins as soon as the outlines of the blastemal skeleton are fairly complete (Figs. 3 and -i). The embryonic cartilage appears slightly kneewards from the center of the shaft of each bone and then extends toward the ends. In CIX, Figs. 3 and 4, and 46 to 53, the cartilage of the femur consists of a bar largest at the knee whence it tapers off toward the hip. The cartilages of the lower leg lie nearly in a common plane. That of the tibia is larger than that of the fibula and toward the knee it broadens out considerably. At this stage the joints consist of a solid mass of mesenchyme, Fig. 55. The tissue imiting the femur and tibia has something the appearance of precartilage.
The further development of the thigh and leg may be conveniently studied by taking up at first the development of the femur and hip-joint, and then that of the tibia, fibula and knee-joint.
The cartilagenous femur expands rapidly at the expense of the surrounding blastemal perichondrium and at the same time acquires adult characteristics.
In an embryo of 11^ mm., CXLIV, Figs.' 5 and G, the shaft of the femur extends almost directly into the hip- joint. Here there is a simple rounded head, distal and dorsal to which a slight projection marks the beginning of the great trochanter. There is nothing corresponding to a true
Charles E. Bardoon 287
"neck/' Similar conditions have heen pictured l)v TTason, oo, for the His embryo So, length 17 mm.
In Embryo XXII, Iciu/th' 20 mm.. Figs. 9 and 10, the head of the feinnr is proportionately larger and between it and the great trochanter the cartilage has developed in snch a way as to give rise to a short neck. Blastemal extensions serve to give attachment to the musculature of the hip and indicate the lesser trochanter and the intertrochanteric ridge. In Embryo CXLV, length 33 m.m.. Figs. 11 and 13, the cartilage has extended into these projections and the main characteristics which distinguish the proximal end of the femur have become established. Even at this stage, however, the neck is proportionately very short and thick. In an embryo of 50 mm., LXXXIV, Fig. 13, the neck is relatively more slender and the head of the femur has become more rounded.
The hip-joint is represented at first by a dense mass of scleroblastema, Fig. 55. The development of the acetabulum by ingrowth and fusion of processes from the iliac, ischial and pubic cartilages has already been described. The cartilagenous joint-cavity is at first quite shallow, Fig. 56. But extension of cartilage into the blastemal tissue which passes from the pelvis over the head of the femur serves greatly to deepen it on all sides except in the region of the cotyloid notch.
The joint-cavity is at first completely filled with a dense blastemal tissue. Fig. 56. While the embryo is growing from 20 to 30 mm. in length cavity formation begins in the tissue lying between the cartilagenous floor of the acetabulum and the head of the femur. The first stage in the process is marked by a condensation of the capsular tissue immediately bordering upon the joint and of the perichondral tissue which at this stage covers the cartilages on their articular surfaces as well as elsewhere. In the region of tlie ligamentum teres a fibrous band is likewise differentiated from the blastema of the joint. The rest of the tissue becomes looser in texture and ultimately is absorbed. Fig. 57. Henke and Reyher, 74, gave a good account of the development of the hip-joint. Moser has discussed the ligamentum teres.
The shaft of the femur at the stages of Embryos CIX and CXLIA^, Figs. 3, 4, 5 and 6 is proportionately very short and thick. For a time it then grows so rapidly that it may become distorted and bent from the resistance offered at each end. But soon adjustment takes place between the skeletal and the neighboring parts and the femur becomes straight and slender. Yet in Embryo CXLV, length 33 mm.. Figs. 11 and 12, it is relatively thicker than in the adult.
The linea aspera is marked during the early development of the femur by a thickening of the pericliondrium in the region where the various
288 Studies of the Development of the Human Skeleton ,
muscle tendons and fascia are inserted. But in embryos up to 50 mm. in length there is no extension of cartilage into this area. Since by this period the shaft is ossified it is evident that no cartilagenous linea aspera is formed.
Ossification begins at an early period kneewards from the center of the shaft. Endochondral calcification begins here in embryos about, or slightly less than 20 mm. in length. Perichondral ossification usually begins in embryos about 25 mm. long, although in Embryos LXXXVI and LXXV, length SO mm., the clavicle alone shows actual bone formation. Ossification of the femur takes place at about the same time as that of the humerus, radius and ulna, and very slightly, if at all, precedes that of the tibia. Ossification of the clavicle and the superior and inferior maxillary bones seems always to begin a little earlier, that of the scapula, ilium, occipital, and ribs, slightly later.
The distal extremity of the femur is large at an early period of differentiation, Embryo CIX, Figs. 3 and 4. In Embryo CXLIV, length IJlf mm.. Figs. 5 and 6, it has expanded laterally and each lateral process has extended dorsally so that fairly well-marked condyles are apparent. These are better formed in Embryo XXII, length 20 mm.. Figs. 9 and 10. In CXLV, length 33 mm., Figs. 11 and 12, the form of the distal extremity of the femur resembles the adult.
The tibia and fibula at first lie nearly in the same plane. Embryo CIX, length 11 mm.. Figs. 3 and 4. As the head of the tibia enlarges toward the knee-joint it comes to lie dorsal to the proximal extremity of the fibula. This may be seen in Embryo CXLIV, Figs. 5 and 6, and more marked in Embryo XVII, length 18 mm.. Fig. 59; XXII, length 20 mm.. Figs. 9 and 10; and CXLV, length 33 mm.. Figs. 11 and 12. In the last embryo the relations of the head of the fibula to that of the tibia are nearly like the adult.
In Embryo CIX, Figs. 3 and 4, the fibula points toward the lateral condyle of the femur and the tibia toward the median, but the long axis of the femur much more nearly meets that of the tibia than that of the fibula. As the head of the tibia enlarges the anterior extremity of the long axis of the bone is carried toward the center of the distal end of the femur while the head of the fibula is pushed toward the side, Figs. 5, 6, 59, 9, 10, so that the long axis of the fibula comes to point lateral to the extremity of the femur. The head of the fibula is held in place by ligaments developed from the skeletal blastema.
The development of the knee-joint in man has been studied by a number of competent observers. Bernays, in 1878, gave a good review of the previous work of von Baer, Bruch, Henke and Eeyher, and an
Charles E. Bardeen 289
accurate description of the processes which take place. Of the more recent articles that of Kazzander, 94, deserves special mention.
Until the embryo reaches a length of about 17 mm. the knee-joint is marked by a dense mass of tissue, Fig, 59. The medullary tissue at the knee, like that at the hip and other joints, is less dense than the surrounding cortical substance, so that when the cartilages of the femur, tibia and fibula are first differentiated they seem to be connected by a tissue which, in some respects, resembles the prochondrium of which they are composed. Fig. 55. But as the cartilages become more definite the apparent continuity disappears. As the musculature becomes differentiated a dense tendon for the quadriceps is formed in front of the knee-joint. This is shown well in Fig. 56. In it the patella becomes differentiated.
In embryos of about 20 mm. the tissue immediately surrounding the cartilages becomes greatl}^ condensed into a definite perichondrium. The peripheral blastemal tissue at the joints becomes transformed into a capsular ligament strengthened in front by the tendon of the quadriceps. Within the joint most of the tissue begins to show signs of becoming less dense, Fig. 56, but the semi-lunar disks and the crucial ligaments, like the ligaments of the capsule are differentiated directly from tlie blastema. Figs. 61 to 65. A knee-joint cavity first appears in embryos about 30 mm. long.
The shafts of the tibia and fibula are incompletely separated in the blastemal stage. The cartilages which arise in the scleroblastema are, on the other hand, separated by a distinct interval, Fig. 50, and as the blastemal elements give way to cartilage the interosseous space becomes larger. This is shown in Figs. 3, 4, 5, 6, 9, 10, 11, 12 and 59. At first short and thick the shafts gradually become more slender in proportion to their length. The fibula at all times smaller, becomes increasingly more slender in comparison with the tibia. In embryos of 30 mm., Figs. 11 and 12, both bones, and especially the fibula, are relatively thick compared with the adult bones.
During a period of rapid development, in embryos of 15 to 20 mm., the tibia and fibula, like the femur, may extend so rapidly in length as to become temporarily distorted by resistance at the ends. This is often especially marked in hardened specimens. Holl, 91, Schomburg, 00, and others have called attention to this distortion.
Ossification begins in the tibia at about the same time that it does in the femur and a little earlier than it does in the fibula. It is usually under way in embryos 25 mm. long. In older embryos it is generally well marked. Figs 11 and 12, Plate V. It begins in both bones kneewards from the center of the shaft and from here spreads toward the
290 Studies of the Develoj)nient of the Human Skeleton
ends of the bones (Fig. 13, Plate V). The development of the distal extremities of the tibia and fibula may best be taken up in connection with the development of the foot.
C. ANKLE AND FOOT.
Of the papers dealing with the early development of the skeleton of the human foot the more important are those of Henke and Eeyher, 74, Leboucq, 82, v. Bardeleben, 83, 85, Lazarus, 96, and Schomburg, 00.
Since the work of Schomburg is the most recent of these and is based on a considerable number of well-prepared embryos, I shall discuss his results somewhat at length in connection with the results which I have obtained. He recognizes four periods in the development of skeletal structures, a mesench^mial, a prochondral, a cartilagenous and an osseous. For the sake of ready comparison I shall take up each of these periods in turn. The fourth period falls within the scope of this paper only in so far as it overlaps the third.
Mesenchymal (hlastemal) period. — This commences during the fifth week of embryonic development. The free extremity of the limb-bud becomes flattened and differentiated into the anlage of the foot and its axial blastema becomes' differentiated into a foot-plate, from which later the bones of the foot are derived. Schomburg states that the axial blastema becomes distinct at the end of the fourth week. In Embryos CCXLI, length 6 mm.: II, length 7 mm.; CLXIII, length 9 mm.; and CCXXI, length 13 mm.^ I find no distinct signs of a foot-plate. In each of the following embryos I find a foot-plate which has not distinctly undergone further differentiation: CIX, length 11 mm.; CLXXV, length 13 mm.: and CYI, length 11 mm. The last is a somewhat pathological specimen. In Fig. 3 a reconstruction of the foot-plate of CIX is shown, in Figs. 51 and 52 transverse sections through this are represented, in Fig. 66 is pictured a longitudinal section through the footplate of CLXXV.
Toward the end of the fifth week, in embryos usually 14 to 16 mm. long, the first differentiation of definite bones is manifested by a condensation of tissue in specific areas. Within these areas of condensed tissue precartilage soon makes its appearance. Schomburg says that the first metatarsal is differentiated distinctly later than the other metatarsals. This I find to be the case in none of Prof. Mall's embryos. I do, however, agree with Schomburg that the metatarsal bones become well differentiated before the tarsals. When the metatarsals and phalanges
' See note 1, Table A. p. 277.
C'harU'8 R. BanUrii 291
become differentiated the portions of the foot-plate between them serve for a short time to form a thick web, Fig. 67.
Prochondrium period. — Schomburg gives a detailed account of the early differentiation of the anlages of the bones of the foot and illustrates his belief as to their nature by several diagrams. Unfortunately he docs not picture the wax-plate reconstructions which he reports having made of a number of early embryos. In Prof. Mall's embryos I find no evidence of the archipterygium-like conditions which Schomburg describes. While it may be true that the somewhat slow development of cartilage in the tarsus is owing to the great alterations from primitive conditions which the human foot has undergone during its phylogeny, and to a certain extent has to repeat during its ontogeny, still the development of the bones of the foot is far more direct than Schomburg's diagrams indicate. In the embryos studied I also fail to find the rudimentary tarsal t)ones described by v. Bardeleben, 83, 85. I have examined six embryos between 15 and 20 mm. long without finding a trace of either the OS intermedium tarsi or the triangularis tarsi. In only one instance have I found the I cuneiform distinctly portioned out into dorsal and plantar divisions by a lateral fissure. Study of adult variation statistically, as so admirably carried out by Pfitzner, 96, for the foot, coupled with comparative anatomy, in this, as in so many other fields, throws more light on a possible phylogeny than is gained from ontological investigation.
Embryo CXLIY, length IJ^ mm., is, of those I have studied, the youngest showing definitely tarsal and metatarsal elements. The general form of the skeleton is shown in Figs. and 6. The differentiation of the tarsal elements is difficult to make out, that of the metatarsals is clear. Webs between the latter still persist, Fig. 67. Webbed digits are sometimes found in the adult (Eobertson).
It is to be noted that the elementaiy condition of the foot of CXLIV corresponds with none of the diagrams given by Schomburg. On the whole the cartilagenous anlages have a position much more nearly resembling the adult. Embryo XLIII, length 16 mm., exhibits pedal characteristics almost identical with those of CXLIV.
It may here be mentioned that in none of the embryos I have studied is the fibula so long as the tibia. Schomburg states that at first it is longer.
The metatarsals when first formed are spread wide apart and gradually become approximated. The diagrams of Schomlnirg indicate a different condition.
292 Studies of the Development of the Human Skeleton
Cartilagenous ^cno(?.— This Schomburg distinguishes from the preceding by the fact that cartilage cells at the centers of the areas of chondrofication show definite cell boundaries and become larger than the surrounding prochondral cells. These changes take place in the various skeletal anlages in the order in which the anlages were originally formed. With the active production of cartilage cells the broad surrounding zone of mesenchyme gives way to a narrower, denser perichondrium. At the same time the form of the skeleton becomes more definite, so that, as Schomburg says, the cartilages of the foot of an embryo at the middle of the third month give a good picture of the adult bones of the foot. The articular surfaces acquire more or less their definite form. I quite agree with Schomburg, in opposition to Henke and Eeyher, that the joints of the foot, like the other joints of the body, are laid down at the start in their definite form and are not moulded into shape by use.
The skeleton of the foot at the time when the cartilage cells at the centers in most of the bones are beginning to be distinctly outlined, has the form shown in Figs. 7, 8 and 59. The tibia is much larger than the fibula and extends further distally. The astragalus has somewhat the form of a rhomboid plate which runs dorsally from the fibular side toward the tibial side on the plantar surface. The calcaneus is rather small and is in direct line with the long axis of the fibula but in a plane lying further plantarwards. The navicular is in a direct line with the astragalus. Its tibial edge lies near the lower end of the tibia. The three cuneiform bones are proportionately broader and thicker than in the adult skeleton. The cuboid is in direct line with the calcaneus. The metatarsals lie less spread apart than at an earlier stage, Figs. 5 and 6. The first phalanx has developed in all of the toes, and in the second toe, the second phalanx as well. At the region of the phalangeal joints there is a swelling of the blastemal tissue.
If now these figures be compared with Figs. 9 and 10, which show the foot of an embryo of 20 mm., the most noticeable change will be seen in the astragalus. This has become considerably thicker. It extends further than the calcaneus. Between the til)ia and the navicular it has so increased in size that the foot is bent toward the fibular side. A much greater interval than in Embryo XVII, Figs. 7, 8 and 59, exists between the two bones.
The calcaneus has extended considerably in length both in a proximal and in a distal direction. The cuneiform bones are becoming crowded together. The cuboid is larger than in XVII. The phalanges are at a similar stage of development. The joints between the metatarsals and phalanges are surrounded by a mass of dense tissue, while the tissue of the joints themselves is of a light texture and resembles prochondrium.
Charles E. Bardeen 393
In Embryo CXLV, length 33 mm., Figs. 11 and 12, the process of cartilage formation has given rise to structures which resemble adult bones. The tibia has greatly expanded at its distal extremity and now articulates. directly with the fibula. These two bones in turn articulate with the well-developed superior articular process of the astragalus. The malleolar process of the tibia is larger and extends further distal than that of the fibula. In an embryo of a corresponding age, however, Schomburg shows that the fibula extends further distal than the tibia. Individual variation may exist.
The astragalus exhibits perhaps more marked alterations in form than any other bone of the foot during the period when the embryo is growing from 20 to 30 mm. in length. Toward the tibia and fibula it develops a well-marked articular process. While this resembles closely the similar process in the adult it is less developed on its fibular side than it is in the adult. As Schomburg has shown the definite adult form is not reached before the fourth month. Toward the calcaneus the bone is well developed and against it exhibits the two characteristic articular surfaces. The posterior of these, compared with the adult, is relatively undeveloped. Distally the bone sends forth a rounded process to articulate with the navicular. In the material at my disposal the whole complex astragalus seems to arise from a single primary center.
The calcaneus, like the astragalus, undergoes marked changes in form during the latter part of the second and the first part of the third month of development. Toward the heel a well-marked tuberosity has made its appearance in Embryo CXLV, Figs. 11 and 12. Distally the bone extends to form a joint with the cuboid. Tibially it has developed a sustentaculum tali for articulation with the astragalus. It is still, however, short in proportion to its width as compared to the adult.
The navicular exhibits no marked changes. On its plantar side and tibial edge it shows a distinct tuberosity.
The cuneiform bones are crowded together and have their characteristic wedge shape. The internal cuneiform is the largest and extends farthest distal. The middle is the smallest.
The cuboid shows a tuberosity. The phalanges, all of which are developed, present no points of special interest.
The joint-cavities begin to develop while the embryo is growing from 25 to 30 mm. in length. As in other cases, so here the blastemal tissue in which the cartilages are developed becomes condensed at their articulating ends and about the joint, while in the region of the joint the tissue becomes less dense and finally disappears leaving a joint-cavity. In
294 Studies of the Dcvclopjiiciit of tlie liiuiuui fSkeleton
embryos of about 30 mm. the joint-cavities of the foot are filled with a loose fibrous tissue, in embryos of 50 mm. definite cavities are to be made out. The sesamoid bones develop later than the period to which this investigation extends.
During the prbgress of form difl:erentiation above described the shape of the foot is markedly altered. At the beginning of the development of the foot the tarsal and metatarsal bones lie nearly, though not quite, in the same plane as the bones of the leg, Figs. 7, 8 and 59. They are so arranged, however, that the foot is convex on its dorsal surface and concave on the plantar, and the projections of the calcaneus and astragalus serve to deepen the plantar fossa. The metacarpals spread widely apart. As differentiation proceeds the metacarpals come to lie more nearly parallel to one another and the tarsal elements become compacted in such a way as to give rise to the tarsal arch. The foot at the same time is flexed at the ankle and turned slightly outwards. The toes are flexed. Fig. G8 shows the extent of the tarsal arch in an embryo of 23 mm.
In the further development of the skeleton of the foot the various constituent structures are elaborated and the foot gradually becomes more flexed and turned toward the fibular side. Yet even in the infant the head of the astragalus is directed more inwards than in the adult. Leboucq, 82, pointed out that the first metatarsal is relatively short in the foetus and points more toward the tibial side than later.
Ossification. — This begins in the metatarsals and phalanges during the third month and is perichondral in nature. The tarsals begin to be ossified considerably later. The center for the calcaneus appears in the sixth month, that for tlie astragalus in the seventh month of fcetal life. The ossification of the other bones begins during the first five years of life. Authorities differ as to the exact time at which the process begins in the various bones. In Quain's Anatomy the following dates are given : cuboid, at birth, external cuneiform, 1st year; internal cuneiform, 3d year; middle cuneiform, 4th year; navicular, 5th year.
I have studied the ossification in the third and fourth months of embryonic life. In an embryo about 4 cm. long, cleared according to the Schultze method, I have found centers of ossification in the 2d, 3d and 4th metatarsals, and in the terminal phalanx of the big toe of each foot. In Embryo XCVI, length 4-^ mm., there is a very thin layer of bone being laid down about the center of the shaft of the 2d, 3d and 4th metatarsals. I have been unable definitely to determine whether or not bone has been deposited in the terminal phalanx of the big toe. In Embryo XCY, length JfG mm., ossification has begun in the 2d, 3d and 4th metatarsals and in the terminal phalanges of the 1st and 2d toes; in Embryos
Charles 11. Barcleen 295
LXXXIY and CLXXXIV, length 50 mm., it is apparent in the 2d, 3d and 4tli metatarsals and in the terminal phalanges of the first three toes. In a cleared embryo, 6 cm. long, there are centers of ossification in all of the metatarsals and torininal phalanges; in one, 8 cm. long, in the first two basal phalanges as well; while in one, 10 cm. long, ossification has begun in all of the metatarsals and the basal and terminal phalanges. We may therefore conclude that ossification in the foot begins in the three central metatarsals and in the terminal phalanx of the first toe toward the end of the third month, and that it is thence extended to the other metatarsals and terminal phalanges before beginning in the basal phalanges.
For a consideration of the development of the individual bones of the foot reference may be made to the excellent paper of Schomburg, oo. The chief points in which my observations conflict with what he describes have been pointed out above. Hasselwander, 03, has recently published a good account of the ossification of the bones of the foot ; and Spitzy, 03, of the structure and development of the infant foot.
SUMMARY.
In general the development of the skeleton of the limb in man corresponds closely with that which is known to take place in other digitates and which has been recently admirably summarized by Braus, 04. Three stages may be recognized, a blastemal, a chondrogenous and an osseogenous. During the chondrogenous stage the chief features of form are reached which characterize the adult structure. The centers for chondrofication correspond closely with those for ossification. The development throughout is fairly direct. No distinct evidences of phylogenetic structures discarded during ontogeny were found in the embryos studied.
LITERATURE QUOTED.
Aeby. — Die Alterverschiedenheiten der menschlichen Wirbelsaiile. Archiv. f.
Anatomie und Physiologie, Anat. Abth., 1879, p. 77. Ancel et Sexcert. — Variation numerique de la colonne vertebrale. Comptes
rend. Assoc, des Anat. Lyon, 1901, p. 158-165.
Les variations des segments vertebro-costaux. Bibliographic Anatom.,
X, pp. 214-239, 1902.
Des quelques variations dans le nombre des vertebres chez rhomme.
Journal de I'Anatomie et de la Physiologie, XXXVIII, 217-258, 1902. Bade, P. — Entwickelung des menschlichen Fuss-skelets von der neunte Embryonalwoche bis ziim 18 Jahre nach Rontgenbildern. Verb. d. gesellsch. deutschen Naturf. u. Aerzte 1899-1900, 463-4G6.
Die Entwickelung des menschlichen Skelets bis zum Geburt. Archiv.
f. mikr. Anatomie, LV, 245-290, 1900.
296 Studies of the Development of the Human Skeleton
Ballantyne. — Spinal column in infants. Edinburgh Medical Journal, 1892. Babdeen. — Costo-vertebral variation in man. Anatomischer Anzeiger XVIII, p. 377, 1900.
Vertebral variation in the human adult and embryo. Anatomischer
Anzeiger, XXV, p. 497, 1904.
Development of the thoracic vertebrae in man. American Journal of
Anatomy, IV, p. 163, 1905. Baedeen and Lewis. — Development of the limbs, body-wall and back in man.
American Journal of Anatomy, Vol. I, p. 1, 1901. V. Baedeleben. — Das Intermedium tarsi beim Menschen. Sitzungsber. d.
Jenaische Gesellschaft f. Med. und Naturw., f. d., Jahr 1883.
Zur Entwickelung der Fusswurzel. Sitzungsb. d. Jenaische Gesell schaft f. Med. und Naturw., f. d., Jahr 1885. Suppl. Bd., XIX. • Hand und Fuss, Verhandl. d. anat. Gesellsch. auf der 8 Versammlung,
1894. Bernays, a. — Die Entwickelungsgeschichte des Kniegelenkes des Menschen
mit Bemerkungen iiber die Gelenke im Allgemeinen. Morphol.
Jahrbuch IV, 403, 1878. BoLK. — Ueber eine Wirbelsaiile mit nur 6 Halswirbeln. Morph. Jahrb.,
XXIX, 84-93, 1901. Braus. — Tatsachliches aus der Entwickelung des Extremitaten Skelets bei
den niedersten Formen. Festschrift f. Haekel, 1904.
Die Entwickelung der Form der Extremitaten und des Extremitaten
skelets. Hertwigs Handbuch der Entwickelungsgeschichte der
Wirbelthiere., 1904. Cunningham. — Proportion of bone and cartilage in the lumbar section of the
vertebral column of apes and several races of man. Journal of
Anatomy and Physiology, 1889, p. 117. DwiGHT, Th. — Methods of estimating the height from parts of the skeleton.
Medical Record, 1894.
Description of human spines. Memoirs Boston Society of Natural
History, V, 237-312, 1901.
A transverse foramen in the last lumbar vertebra. Anatomischer
Anzeiger XX, 571-572, 1902. Feeling, H.- — Die Form des Beckens beim Foetus und Neugeborenen und ihre
Beziehung zu der beim Erwachsenen. Archiv. f. Gynsekologie,
X, 1876. Flower. — Osteology of the Mammalia. FoL. — Sur la queue de I'embryon humain. Comptes Rendus de I'academi, C,
p. 1469, 1885. FiJEBRiNGER. — Morphologische Streitfi-agen. Morph. Jahrbuch XXX, 1902. Gegenbaur. — Vergleichende Anatomie der Wirbelthiere mit Beriicksichtigung
der Wirbellosen, 1, 1898. Gbuber. — Ueber die Halsrippen des Menschen mit vergleich. anat. Bemerkungen. Memories de I'Acad. des Sciences de St. Petersbourg, XIII,
1869, No. 2. Hagen. — Die Bildung des Knorpelskelets beim menschlichen Embryo. Archiv.
f. Anatomie und Physiologic. Anat.. Abth.. 1900, p. 1.
Charles E. Bardeen 297
Hakbison, R. G. — On the occurrence of tails in man with a description of the
case reported by Dr. Watson. The Johns Hopkins Bulletin, XII, 121 129, 1901. Hasselwander.— Untersuchungen iiber die ossification des menschlichen
Fuss-skelets. Zeitschrift f. Morphologie und Anthropologie, V, 438 508, 1903. Henke und Reyher. — Studien iiber die Entwickelung der Extremitaten des
Menschen insbes. der Gelenkflaschen. Sitzungsb. d. K. Akad. d.
Wiss. Math.-naturw. Klasse Wien, LXX, 3d Pt, p. 217, 1874. HoLL, M. — Ueber die richtige Deutung der Querfortsatze der Lendenwirbel
und die Entwickelung der Wirbelsaiile des Menschen. Sitzungsb. d.
K. Akad. d. Wiss. Math.-naturw. Klasse. Wien. LXXXV, pp. 181 232, 1882.
Ueber die Entwickelung der Stellung der Gliedemassen des Menschen.
Sitzungsb. d. K. Acad. d. Wiss. Math.-naturw. Klasse. Wien., C, 3d
Ft, p. 12, 1891. Kazzander, G. — Sullo svilluppo dell' articolazione del ginocchio. Monitore
Zoologico Italiano, V, p. 220, 1894. Klaatsch, H. — Die wichtigsten Variationen am Skelet der freien unteren Ex tremitat des Menschen und ihre Bedeutung f. das Abstammungs problem. Ergebnisse d. Anatomie und Entwickl., X, pp. 599-719, 1900. KoNiKOw, M. — Zur Lehre von der Entwickelung des Beckens und seiner
geschlechtlichen Differenzierung. Arch. f. Gynsekologie, XLV, p. 19,
1894. Lazabus.^ — Zur Morphologie des Fuss-skelets. Morph. Jahrbuch, XXIV, 1896. Leboucq. — Le developpement du premier metatarsien et de son articulation
tarsienne chez I'homme. Archives de Biologie III, 335, 1882.
Recherches sur les variations anatomiques de la premiere cote chez
I'homme. Archives de Biologie, XV, p. 125, 1898.
Low. — Description of a specimen in which there is a rudimentary first rib, with thirteen pairs of ribs and twenty-five presacral vertebrae. Journal of Anatomy and Physiology, XXXIV, 451-457, 1901.
LuBSEN, J. — Zur morphologie des Ilium bei Saiigern. Overdruk nit Petrus Camper, Dl. II, Afl. 3.
Mehneet, E. — Untersuchungen iiber die Entwickelung des Beckengiirtels bei einigen Saiigethieren. Morphol. Jahrbuch, XVI, pp. 97-112, 1889.
Mebkel. — Beckenwachstum: Anat. Hefte I, 121-150, 1902.
Mollier. — Die paarigen Extremitaten der Wirbelthiere. Anatomische Hefte, 1893, 1895, 1897.
MosEB. — Das Wachstum der menschlichen Wirbelsaiile, Dissertation Strassburg, 1889.
Ueber das Ligamentum teres des Hiiftgelenkes. Schwalbes Arbeiten,
II, p. 36. Papillault, G. — Variations numeriques des vertebres lumbaires chez I'homme.
Bulletins de la Soc. d. Anthropologie de Paris, IX, 198-222, 1900. Patebson, a. M. — The human sacrum. Scientific transactions of the Royal
Dublin Society, V, p. 123, 1893. Petebsen. — Untersuchungen zur Entwickelung des menschlichen Beckens.
Arch. f. Anatomie und Physiologie, Anat., Abtheilung, 1893, pp.
67-96.
23
298 Studies oi' the Developjnent of the Human Skeleton
PriTZNEB, W. — Die Variationen im Aufbau des Fuss-skelets. Morphol. Ar beiten, VI, 245, 189G. PosTH, M. — Le Sacrum. Thesis, Paris, 1897. Rabl. — Gedanlien und Studien iiber den Ursprung der Extremitafcen.
Zeitschr. f. wiss. Zool. LXX, 474-558, 1901.
Ueber einige Probleme der Morphologie. Anat. Anz. Erganz. Hefte,
XXIII. 1903. Rambaud and Renault. — Origine et developpement des Os. Paris, 1864. Ravenal. — Die Massenverhaltnisse der Wirbelsaiile und des Riickenmarks
beim Menschen. Zeitschrift f. Anatomie und Entwickelungsg., II,
343. 1877. Retteeer. — Ebauche squelettogene des membres et developpement des articulations. Journal de I'Anatomie et Physiologie, XXXVIII, 473-509,
580-623, 1902. Robertson, W. G. — A case of supernumerary and webbed fingers. Edinburgh
Medical Journal, XIV, 535-536. RoMiTi, G. — Sui caratteri sessuali nel bacino del neonato. Atti della society
Toscana di Science naturali, VIII, 1892, Pisa. Rosenberg, E. — Ueber die Entwickelung der Wirbelsaiile und das centrale
carpi des Menschen. Morphol. Jahrbuch, I, p. 83, 1876.
Ueber eine primitive Form der Wirbelsaiile des Menschen. Morphol.
Jahrb., XXVII, 1-118, 1899. RucKEET. — Ossif, des menschl. Fussskelts. Sitzungsb. d. Koenig. Bay. Akad,
Miinchen, Mat. Nat. Kl. 1901, 65-72. RuGE. — Die Entwickelung des Skelets der vordern Extr. von Spinax niger.
" Morphol. Jahrb., XXX, 1-27, 1892. ScHOMBUEG, H. — Untersuchungen der Entwickelung der Muskeln und
Knocken des menschlichen Fusses. Dissertation, Gottingen, 1900. Spitzy, H. — Ueber Bau und Entwickelung des kindlichen Fusses. Jahrb. f.
Kinderheil, 1903. Steinbach. — Die Zahl der Caudalwirbel beim Menschen. Dissertation. Berlin, 1889. SzAWLOwsKi. — Ueber einige Seltene Variationen an der Wirbelsaiile beim
Menschen. Anatomischer Anzeiger, XX, 305, 1901. Tenchini. — Die una nuova maniera di compenso nelle anomalie numeriche
vertebrali dell' uomo. Archivio per I'Anthropologia, XXIV, Firenze,
1894. Thilenius. — Untersuchungen iiber die morphologische Bedeutung accesso rischer Elemente am menschlichen Carpus (und Tarsus). Morphol.
Arbeiten. V. 1895. Thomson, A. — The sexual differences of the foetal pelvis. Journal of Anatomy and Physiology, XXXIII, pp. 3 and 359-380, 1899. TopiNARD, P. — Anomalies de nombre de la colonne vertebrate chez I'homme.
Revue d' Anthropologie, VI. 577, 1877. Unger and Brugsch. — Zur Kenntniss der Fovea und Fistula sacro-coccygea s.
caudalis, etc. Archiv. f. mikr. Anatomie, LXI, 151-219, 1903. Veit. — Die Entstehung der Form des Beckens. Zeitschr. f. Geburtsh. und
Gynfekologie, IX, 347, 1889. WiEDERSHEiM. — Das Gliedmassenskelet der Wirbelthiere, Jena, 1892.
Charles R. Bardeen
299
LIST
A. A. Pr Ca-l.—
Chd Co: C. Pr Cu. C. V. Der. Disk D.L. D.M. F. D. M. Fi. F.N. F. Pl F. V. E. H. Pr. Ids. M. Idr. M II. Bl. Is. Is. A. L Ls. Pl. L. T. Myo
OF ABBREVIATIONS USED IN LETTERING THE FIGURES. -Anterior articular process. M. D. R. — Membrana reuniens dorsalis.
Ccelom.
-Cliorda dorsalis.
-Coccygeal.
-Costal process.
-Cuboid.
-Cardinal vein.
-Dermis.
-Intervertebral disk.
-Dorsal ligament.
-Dorsal musculature.
-Fascia of dorsal musculature.
-Fibula.
-Femoral nerve.
-Foot-plate.
-Fissure of v. Ebner.
-Haemal process.
-Interdiscal membrane.
-Interdorsal membrane.
-Iliac blastema.
-Ischium.
-Intersegmental artery.
-Lumbar.
-Lumbo-sacral plexis.
-Ligamentum teres.
-Myotome.
N. Pr. — Neural process. 0. F. — Obturator foramen. 0. N. — Obturator nerve. P(Z.— Pedicle. Pch. 8. — Perichordal sheath. P. L. — Poupart's ligament. P. A. Pr. — Posterior articular process. P. — Pubis. Rib. — Rib.
S. — Sacral vertebra. S. Bl. — Scleroblastema. S.N. — Sciatic nerve Sptm. — Perichordal septum. 8p. C. — Spinal chord. Sp.G. — Spinal ganglion. Sp.N. — Spinal nerve. Sp. Pr. — Spinous process. T. R. — Tendon of r. abd. muscle. T. — Thoracic. Ti.— Tibia. Trap. — Trapezius muscle. Tr. Pr. — Transverse process, y. L. — Ventral ligament, y. B. — Vertebral body.
Figs. 1-12 wax-plate method, glycerine method.
DESCRIPTION OF PLATES. Plates I-V. A series of figures drawn from models made by the Born
Fig. 13 from an embryo cleared by the Schultze alkaline,
Plate I.
Fig. 1. Skeleton of Embryo II, length 7 mm. About 20 diam. the reconstruction was made free-hand from drawings.
In part
Plate II.
Fig. 2. Right half of the distal portion of the skeleton of Embryo CLXIII, length 9 mm. 25 diam.
Figs. 3 and 4. Right half of the distal portion of Embryo CIX, length 11 mm. 25 diam. (4) lateral, (5) median, view. The prochondrium of the pubis, ilium. Ischium, femur, tibia and fibula are represented by stippling.
Plate III.
Figs 5 and 6. Distal portion of the right half-skeleton of Embryo CXLIV, length Hi mm. 25 diam. The prochondrium of the neural arches, the
300 Studies of the Development of the Huiiiaii Skeleton
vertebral bodies, the ilium, ischium, femur, tibia, fibula and of the bones of the foot is represented by stippling. The last are but slightly differentiated at this period.
Plate IV.
Figs. 7 and 8. Dorsal and plantar views of the cartilages of the left leg and foot of Embryo XVII, length 18 mm. 20 cliam.
Figs. 9 and 10. Lateral and median views of the distal portion of the right half of the cartilagenous skeleton of Embryo XXII, length 20 mm. 20 diam.
Plate V.
Figs. 11 and 12. Median and lateral views of the distal portion of the right half of the cartilagenous skeleton of Embryo CXLV, length 33 mm. 10 diam. The centres of ossification of the femur, tibia and fibula are shown.
Fig. 13. Lateral view of the left leg of an embryo 5 cm. long. 5 diam. For the sake of facilitating comparison, a mirror picture has been drawn and a technique has been used similar to that employed for illustrating the models. The centers of ossification of the ilium, femur, tibia, fibula, the three middle metatarsals and the terminal digits are shown. The position of the various structures has probably been somewhat distorted during the preparation of the specimen.
Plates VI and VII.
Figs. 14-28. Transverse sections through the twelfth thoracic and first two lumbar vertebrae of a series of embryos. IJf diameters. Figs. 14-16, Embryo CLXXV, length 13 mm.; Figs. 17-19, Embryo CCXVI, length 17 mm.; Figs. 20-22 Embryo XXII, length 20 mm.; Figs. 23-25, Embryo XLV, length 28 mm.; Figs. 26-28, Embryo LXXXIV, length 50 mm.
Plate VIII.
Figs. 29-36. Transverse sections somewhat oblique through several vertebrae of various embryos. 14 diam. Fig. 29, 4th sacral vertebra of Embryo CIX, length 11 mm.; Figs. 30-32, 1st, 2d, and 3d sacral vertebrae of Embryo X, length 20 mm.; Figs. 33 and 34, 1st and 2d sacral vertebrae of Embryo CCXXVI, length 25 mm.; Fig. 35, 2d sacral vertebra of Embryo XLV, length 28 mm.; Fig. 36, 2d sacral vertebra of Embryo LXXXIV, length 50 mm.
Plate IX.
Figs. 37-40. Obliquely cut frontal sections through the sacral region of several embryos. I4 diam. Fig. 37, Embryo CLXXV, length 13 mm.; Fig. 38, Embryo CCXVI, length 11 mm.; Fig. 39, Embryo CLXXXVIII, length 11 mm.; Fig. 40, Embryo LXXXVI, length 30 mm.
Plate X.
Figs. 41-43. Sections through the coccygeal region of several embryos. IJf diam. Fig. 41, frontal section of Embryo CLXXV, length IS mm.; Fig. 42, sagittal section of Embryo CXLV, length 33 mm.; Fig. 43, frontal section of Embryo LXXXIV, length 50 mm.
Charles R. Bardeen 301
Fig. 44. Diagram to show the curvature of the spinal column, the proportional lengths of the various regions, the relation of the acetabula to the sacral region and the direction of the long axis of the femur in a series of embryos 7 to 50 mm. in length, and in an adult. Each curved line represents the chorda dorsalis of an individual. The cervical, lumbar and coccygeal regions of this are represented by the heavy, the thoracic and sacral by the light portions of the line. The approximate position where a line joining the centers of the two acetabula would cut the median plane is represented at "a." For Embryo II, In which the skeleton of the leg is not yet differentiated the position of the future acetabula is deduced from Embryo CLXIII, length 9 mm. (See Fig. 2.)
The line passing in each instance from "a" and terminating in an arrow point represents the long axis of the femur. For Embryo II, this line is pointed toward the centre of the tip of the limb-bud. From " a " in each instance a perpendicular is dropped to a line connecting the two extremities of the sacral region. The numbers refer to the following embryos:
2, II Length 7 mm.
109, CIX " 11 "
144, CXLIV " 14 "
108, CVIII " 20 "
145, CXLV " 33 "
184, CLXXXIV " 50 "
Ad. Adult.
Plate XI.
Fig. 45. Longitudinal section through the center of the limb-bud of Embryo CLXIII. i// diam. Compare with Fig. 2.
Figs. 46-52. A series of cross-sections through the right leg of Embryo CIX, length 11 vim.
Fig. 53. Outline of the blastemal skeleton with the regions marked through which the sections 46-52 pass. 1^ diam. Compare with Figs. 3 and 4.
Plate XII.
Fig. 54. Section from Embryo CXLIV, length 14 mm., showing the pubic, iliac and ischial cartilages. 14 diam.
Fig. 55. Section passing longitudinally through the femur and tibia of Embryo CLXXV, length 13 mm. A portion of the foot-plate is shown cut obliquely. 14 diam.
Fig. 56. Longitudinal section through the ilium, femur, and tibia of Embryo XXII, length 20 mm. 14 diam.
Fig. 57. Section through the pubis, ilium, ischium and head of the femur of Embryo CCXXVII, length 30 mm. The hip-joint cavity shows well. It does not extend into the region of the ligamentum teres. 14 diam.
Fig. 58. Section through the ilium, ischium and head of the femur of Embryo LXXIX, length 33 mm. Calcification is beginning in the ilium.
Plate XIII.
Fig. 59. Section through the leg and foot of Embryo XVII, length IS mm. The section does not pass through the cartilage of the 1st metatarsal.
302 Studies of the Development ol the Human Skeleton
Fig. 60. Section through the pubis, ischium, femur, fibula, calcaneus, cuboid and the 4th metatarsal cartilages of Embryo LXXIV, length IG mm. Iff diameters.
Figs. 61-65. Sections through the knee-joints of several embryos. i-J diam; 61, CCXXIX, length about 20 mm.; 62, LXXXVI, length 30 mm.; 63, LXXV, length SO mm.; 64 and 65, CXLV, length 33 mm.
Fig. 66. Longitudinal section through the knee-joint, tibia and foot-plate of Embryo CLXXV, length 13 mm.
Fig. 67. Section through the foot of Embryo CXLIV, length IJt mm.
Fig. 68. Section through the foot of Embryo LVII, length 23 mm.
The models from ivhich tlie illustrations in this article were drawn have been reproduced hy Dr. B. E. Dahlgren at the American Museum of Natural History, New Yorh, N. Y., and arrangements may he made for securing copies hy applying to the Director of the Museum.
DEVELOPMENT CF THE HUMAN SKELETON
C. R. BARDEEN
PLATE I
II, LENGTH 7 MM.
AMERICAN JOURNAL OF ANATOMY— VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE II
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CIX, LENGTH 11 MM.
Anlages of cartilege.
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CIX, LENGTH 11 MM.
AMERICAN JOURNAL OF AN ATOM Y--VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BAROEEN
PLATE 111
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AMERICAN JOURNAL OF AMATOMY- VOL. IV
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C. R. BARDEEN
PLATE IV
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FIs.lO
XXII, LENGTH 20 MM
AMERICAN JOURNAL OF ANATOMY—VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE V
LXXXIV, LENGTH 50 MM.
AMERICAN JOURNAL OF ANATOMY—VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE VI
fiS-22
Fig. 2 5
AMERICAN JOURNAL OF ANATOMY— VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE VII
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12 rib
Fig. 2 6
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AMERICAN JOURNAL OF ANATOMY—VOL. I\
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE VIII
AMERiCAN JOURNAL OF ANATOMY—VOL. IV
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C. R. BARDEEN
PLATE IX
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AMERICAN JOURNAL OF ANATOMY— VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE X
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AMERICAN JOURNAL OF AN ATOMY--VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE XI
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AMERrCAN JOURNAL OF ANATOMY--VOL. IV
24
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE XII
Fig-. 58
AMERICAN JOURNAL OF AN ATOM Y--VOL. IV
DEVELOPMENT OF THE HUMAN SKELETON
C. R. BARDEEN
PLATE XIII
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Fig.n
AMERICAN JOURNAL OF ANATOMY — VOL. IV
A COMPOSITE STUDY OF THE SUBCLAVIAN AETERY IN
MAN.
BY
ROBERT BENNETT BEAN, M. D.
Assistatit in Anatomy, Johns Hopkins Medical School, Baltimore, Md.
With 7 Figures and 18 Tables.
Several years ago Hitzrot' made a study of the axillary artery based upon records made in the Anatomical Laboratory of the Johns Hopkins University. To supplement this, the following study of the subclavian artery was made at the suggestion of Dr. Harrison. The clinical features relating to the artery are given in another article."
That there is need for further data concerning the ramifications of this artery is apparent when the accompanying figures, taken from a number of universally recognized authorities, are compared. From them it is seen, that, while certain branches such as the vertebral and internal mammary are represented in the same manner by all, there is the widest divergence with regard to the other branches.
The records which underlie the present study were made by myself, from the dissections by students of anatomy, upon Bardeen's charts.' Dissections from 129 subjects are recorded, 60 from the left side of the body and 69 from the right side. Some of these records are complete to the minutest detail; nearly all give the origin of the main branches; while a few are incomplete, giving only the subclavian artery and some of its branches, or only a few branches without the subclavian artery. The distribution of the vertebral artery inside the skull was not worked out, because many of the cadavers were not obtained .until after the brain had been removed. The distribution of the internal mammary artery was worked out completely in but 28 cases because of the removal of the sternum at the autopsy in the others.
^Hitzrot, Johns Hopkins Hospital Bulletin, Vol. XII, 1901. Bean, Johns Hopkins Hospital Bulletin, Vol. XV, 1904. 'Bardeen, Outline Record Charts, Johns Hopkins Press, Baltimore, 1900. American Journal of Anatomy. — Vol. IV.
A.
-^sj.T.e.
AI.S
AMJ^
Fig. 1. Branches of the subclavian artery according to dilTerent authors. A, according to Quain, Testut and Gray; B, according to Henle; C, according to Tiedemann; D, according to Spalteholz and Toldt (B. N. A) ; £, according to Gegenbaur; I'\ according to Sappey.
The lettering on all the figures is alike and as follows: I, II and III, the three parts of the subclavian artery; A. V., arteria vertebralis; A. M. I., arteria mammaria interna; T. T. C, truncus thyreo-cervicalis; A. T. 7., arteria thyroidea inferior; A. T. 5'., arteria transversa scapula; A. T. C, arteria transversa colli; E. A. T. C, ramus ascendens transversa colli; S. D. T. C, ramus descendens transversa colli; A. 0. S., arteria cervicalis superficialis ; A. C. A., arteria cervicalis ascendens; T. 0. C, truncus costo-cervicalis; A. I. S., arteria intercostalis suprema; A. C. P.y arteria cervicalis profunda; G. T., common trunk.
Robert Beuuett Bean
305
While numerous variations in the origin and distribution of the branches of the artery are observed in my study, it is nevertheless possible to classify the cases, for they are found to fall naturally into a number of distinct types. In section A of this work it is proposed to describe these types. This will be followed in section B by a description of the origin and distribution of the individual branches, while in section C the results of the present study will be discussed in their relation to the previous work upon the subject, and illustrative tables will be appended.
AC.R
RD.TjC.
tp
FiG. 2. Type I, occurring in S0% of the specimens, 22^ on the right side, and S% on the left side of the body. For index to lettering see Fig. 1.
The three divisions of the subclavian artery referred to throughout this work are: Part I, that portion medial to the scalenus anticus muscle; Part II, posterior to it; and Part III, lateral to this muscle.
The records given are from 74 male Negroes, 16 female ISTegroes, 21 male Caucasians and 3 female Caucasians. The race and sex are not determined in 15 subjects. The Negroes are the American variety, and possibly all of them have a trace of the Caucasian mixed with the Negro, the proportion in an}^ case being uncertain.
30G
A Composite Study of the Subclavian Artery in Man
Section A. — Types of Eamification,
The mode of ramification of the subclavian artery is found to be divided into five types, depending upon the origin of the large branches. The distribution of these branches is practically the same in all cases.
Type I (Fig. 3) occurs in 30% of the cases classified, 22% being on the right side of the body and 8% on the left side. In this type the vertebral and internal mammary arteries rise from Part I ; the inferior thyroid and suprascapular arteries rise from a common trunk which comes from Part I, and between these two arteries rises the superficial
ACR
RATC
R.D.T.C.
Fig. 3. Type II, occurring in 27% of the specimens, 22fo on the left side, and 5% on the right side of the body. For index to lettering see Fig. 1.
cervical artery ; the ascending cervical artery rises ' from the inferior thyroid; and the transverse cervical artery and the costo-cervical trunk rise from Part II. Each of the branches often has a separate origin. There are in this type 19 male negro subjects, 2 female negro subjects, 5 male white subjects, 2 female white subjects, and 4 subjects in which the sex and race are not determined.
Type II (Fig. 3) is found in 27% of the cases classified, 22% being on the left side of the body and 5% on the right side. The vertebral
Eobert Bennett Bean
307
and internal mannnary arteries rise from I'art I ; the inferior thyroid, suprascapular and transverse cervical arteries rise from a common trunk which comes from Part I, and is known as the tliyroid axis; the superficial cervical artery is absent, its place being taken by small branches from the transverse cervical artery; the ascending cervical artery rises from the inferior thyroid artery, as it does in practically all the cases of all the types; and the costo-cervical trunk rises from Part II. The internal mammary artery rises from the thyroid axis five times in this type — four times in infants — showing a bunching of the branches.
ACP
C.T. KKTt
RD.T.C.
ATS.
Fig. 4. Type III, occurring in 22^ of the specimens. For index to lettering see Fig. 1.
There are in this type 18 male negro subjects, 2 female negro subjects, 3 male white subjects, 1 female white subject, and 1 subject in which the sex and race are not determined. Types I andll are the representative types for the right and left sides of the body respectively. Cf. Fig. 7, A and B, pp. 314 and 315.
Type III (Fig. 4) with slight variations occurs in 22% of the cases classified, 25 times in all, 13 on the right side of the body and 12 on the left side. The vertebral and internal mammary arteries, and the costocervical trunk rise from Part I in this type and in the two remaining
308 A Composite Study of the Subclavian Artery in Man
types. Tlie inferior thyroid artery rises from Part I, the transverse cervical artery rises from Part II, and the suprascapular artery rises from Part III, or from the axillary artery (9 times). This type may be considered a subtype of the first, Type I, showing the extreme separation of the origin of the branches and no bunching. There are in this type 11 male negro subjects, 4 female negro subjects, 7 male white subjects, and 3 subjects in which the sex and race are not determined.
Type IV (Fig. 5) is found in 12% of the cases classified, 14 times in all, present in equal number on each side of the body. The inferior thy
AT..C. T.C.C. ~^-^„
ATS
RDTC.
Fig. 5. Type IV, occurring in 12% of the specimens. Fig. 1.
For index to lettering see
roid artery rises with a common trunk from Part I. From the common trunk rise the suprascapular and transverse cervical arteries. This type may be considered as a subtype of the second. Type II, in which the branches are often bunched. There are in this type 4 male negro subjects, 3 female negro subjects, 3 male white subjects, and 4 subjects in which the sex and race are not determined.
Type V (Fig. 6) occurs in 10% of the cases classified. The inferior thyroid and superficial cervical arteries rise by a common trunk from
Eobert Bennett Bean
309
Part I; the suprascapular artery rises from the internal mammary artery. The type is of interest from this fact and because of its frequent occurrence in the cases studied.
Section B. — Desckiption of the Individual Branches.
In its origin the vertebral artery is the most constant of all the branches of the subclavian artery. It arises in every case, with three exceptions, from the posterior and superior aspect of Part I, and is the first and largest branch. It is associated with other arteries in its origin
Fig. 6. Type V, occurring in 10% of the specimens. For index to lettering see Fig. 1.
from a common trunk but four times, with the inferior thyroid three times, and the thyroid axis once. It comes from the arch of the aorta between the origin of the left common carotid and the left subclavian arteries three times. In one case on the right side the vertebral artery is double, two small arteries arising from Part I and entering the 6th vertebral foramen together. The artery enters the 4th foramen once; the 5th, 4 times; the 6th, 88 times; and the 7th, 4 times. Tiedemann states that this artery enters any one of the vertebral foramina from the
310 A Composite Study of the Subclavian Artery in Man
1st to the 7th, most frequently the (ith, and most infrequently the 7th. He also mentions a double vertebral artery, one arising from the inferior thyroid artery, the other from the subclavian, uniting at the 4th cervical vertebra. Quain gives a chart of a similar double vertebral artery.
The internal mammary artery arises alone from Part I in 80% of the cases, and is associated with other arteries by origin in a common trunk in 20% of the cases, arising with the thyroid axis in 10% of the latter, with the suprascapular in 10% of them, and with tlic transverse cervical and suprascapular once. The distribution of the artery is worked out in minute detail only 28 times. A lateral tlioracic artery is found five times in the 28. It is as large as the internal mammary, is derived from the latter close to its origin from the subclavian, and passes between the parietal pleura and the ribs along the anterior axillary line, sending branches into the intercostal spaces from the 1st to the 9th, and losing itself in one of these spaces or in the diaphragm. A lateral thoracic artery is mentioned by Quain, Tiedemann, Henle, and other anatomists, but is given as a very rare anomaly. Intercostal branches come from the internal mammary as single arteries posterior to the intercostal spaces, sending one branch to the superior part and another to the inferior part of the spaces; or they arise posterior to the costal cartilages, sending a branch above and one below the adjoining rib ; or there are two intercostal branches to each space, one below the rib above it, the other above the rib below it. Any two or all three of these arrangements may be found on one side of a subject. In 54% of the subjects there are two branches to each intercostal space, in 46% only one.
The thyroid axis' is found as shown in Type I, Fig. 2, in 30% of the cases, 22% of these being on the right side of the body, and 8% on the left side. It is present as shown in Type II, Fig. 3, in 27% of the cases, 22% of these being on the left side of the body, and 5% on the right side. Quain and Gray give Type II as normal. Tiedemann, Henle, Gegenbaur, Sappey, Testut and other French and Grcrman anatomists give Type I as the most frequent.
The inferior thyroid artery^ arises as shown in Type I in 35% of the subjects; it arises from Part I as a single branch in 33% of the subjects, and as shown in Type II, in 32% of the subjects.
The suprascapular artery" arises as shown in Type I in 3G% of the subjects; in Type II in 34%, and from the subclavian alone as a single branch in 30% of them.
This artery is absent 4 times, double 3 times, and very small 4 times. The long thoracic artery arises from it once.
Table 2, p. 318. = Table 3, p. 318. "Table 5, p. 319.
Robert Bennett Bean 311
The transverse cervical artery' arises from Part II in 39% of the subjects, from Part I in 36% of the subjects (alone or with the thyroid axis), and from Part III,' or from the axillary artery in 25% of them. Quain gives the most frequent origin of the transverse cervical artery from the thyroid axis, dividing into the jjosterior scapular and superficial cervical; tlie next in frequency being the posterior scapular from Part III and the superficial cervical from the thyroid axis; the least frequent mode of origin being from Part III, and dividing into posterior scapular and superficial cervical arteries. We found the following approximately :
The transverse cervical artery arises on the right side from Part II, dividing into ascending [superficial cervical (?)] and descending (posterior scapular) rami, and on the left side from the thyroid axis, dividing into ascending and descending rami, having previously given off the superficial cervical artery. The ascending ramus of the transverse cervical artery arises lateral to the levator scapulae muscle, and, dividing almost immediately, sends one branch parallel to the superior lateral border of the trapezius and beneath it to the occiput. The other branch passes parallel to the inferior lateral border of the same muscle and beneath it to the level of the seventh thoracic vertebra, sending a large branch to the rhomboid muscles. The descending ramus follws the prescribed course of the posterior scapular artery as given in English and American text-books. The relation of the two sides of the body with reference to the origin of the transverse cervical artery shows the two sides alike in 29 subjects, unlike in 13. In 10 of the latter the artery arises from Part II on the right side, and from the thyroid axis on the left side.
The superficial cervical artery ' is considered to be a branch that passes from the transverse cervical artery in 60% of the subjects, from the inferior thyroid artery in 22% of the subjects, and from the suprascapular artery in 18% of the subjects, terminating just beneath the lateral border of the trapezius muscle. The artery is more commonly a number of small branches arising along the transverse cervical artery as it traverses the neck. The ascending ramus of the transverse cervical artery is described by some anatomists as the superficial cervical artery (Quain).
The casto-cervical trunl" a small short artery, arises from Part I in 90% of the subjects; from Part II in 9% of the subjects, and from
^Tables 6, 7, and 8, p. 319.
« Table 9, p. 320.
"Tables 10 and 11, p. 320.
312 A Composite Study of the Subclavian Artery in Man
Part 111 in 1% of them, dividing almost immediately into the superior intercostal and the deep cervical arteries. The origin from Parts II and III is on the right side of the body in all cases.
The supenor intercostal artery '" arises on the right side of the body from the costo-cervical trunk in 41% of the subjects; from Part II in 10% of the subjects, and from Part I in 3% of them. It arises on the left side of the body from the costo-cervical trunk in 38% of the subjects, and from Part I in 8% of them.
The deep cervical artery "^ arises from the costo-cervical trunk in 83% of the subjects; from the subclavian artery in 13% of them, and from the inferior thyroid in 4% of them. It passes above the first rib in 82%. of the subjects, and below it in 18% of them. The distribution of the deep cervical artery varies in inverse proportion to that of the ascending cervical and the superior intercostal arteries.
SECTioisr C. — Discussion.
First. — We have demonstrated that the branches are arranged in a different manner on the two sides of the body. Fig. 7 shows this.
This figure represents the most usual arrangement of the branches of the subclavian artery as found on each side of the body, the difference between the two sides of the body being chiefly in the origin of the transverse cervical artery." The type shown on the right side of the body occurred in 51% of all the cases classified on that side. The type shown on the left side of the body occurred in 55% of all the cases classified on that side. The distribution of the anterior branches is put on the right side of the body, and that of the posterior branches on the left side of the body in this figure.
Second. — The number of branches arising from Part II on the right side is more than double those from the same part on the left side, counting all cases. This is due to the origin of the transverse cervical artery and occasionally (11 times) the superior intercostal artery from Part II on the right side."
Third. — The relation of the branches to age discloses the apparent abnormality of infantile subclavian arteries. There are 23 infant subjects worked out, 17 male negro, 4 female negro, and 2 male white. No two subjects show the same arrangement, all being irregular.
" Table 10, p. 320.
"Table 11, p. 320.
^= Tables 12, 13, 14, 15, and 16, pp. 320, 321, 322, and 323.
"Tables 5. 10, 13, and 14, pp. 319, 320, and 321.
Robert Bennett Beau 313
Two striking features are noticed. In the first place there seems to be a tendency for the branches to be bunched from Part I. The internal mammary artery arises 4 times with the thyroid axis, and the suprascapular artery arises twice from the internal mammary artery. In the second place the suprascapular artery is small in five cases, and does not extend beyond the suprascapular notch in these cases, its place being taken by the dorsal scapular artery. There are 2 other cases with inosculation around the neck of the scapular between these two arteries, the suprascapular being like a continuation of the dorsal scapular artery. Knowledge of the previous condition of the subject as to age, habits, and family history, and dissection of subjects that had died at the ages of 1, 5, 10, 15, 20, and 25 years, etc., would be of value in studies similar to this one.
Foiirih. — There are 74 male negro and 16 female negro subjects, and 21 male white and 3 female white subjects from which records were made. In 15 subjects the race and sex are not determined. In view of the small number of female and white subjects, the relation of sex and race will hardly admit of discussion. Many of the subjects are mulattoes, or mixed bloods. The number of anomalies, variations, and queer types is uncommonly large.
May we not explain the occurrence of this large number of abnormalities by the well-known biological law that hybrids tend toward variation ? The question is an open and an interesting one.
Fifth. — Free anastomoses by a definite arterial trunk were found in connection with the suprascapular, deep cervical and superior intercostal arteries. The suprascapular artery inosculates with the dorsal scapular artery posterior to the neck of the scapula, 17 times, or in 16% of all cases. The trunk was from 2 to 5 mm. in diameter. The superior intercostal artery anastomoses with the superior aortic intercostal artery 31 times, in every case where it is looked for. The anastomosis is found to take place :
At the second intercostal space IG times
At the third intercostal space 10 times
At the fourth intercostal space 5 times
The trunk is very small, only a minute tube in some cases. The deep cervical, " profunda cervicis," anastomoses with the " princeps cervicis " from the occipital in 11 cases, 10% of all. The trunk is of good size, frequently about 5 mm. in diameter.
Sixt]i. — Anomalies when present are found as a rule on each side of the same subject. Tlie most frequent anomaly met with in the dissec25
RDIC^
Fig. 7-A. The right subclavian artery. See Fig. 1 for index to lettering.
A.e.A
Rnie.
D.C.P
Fig. T-B. The left subclavian artery of the same body as Fig. 7-A. See Fig. 1 for index to letterintr
316 A Composite Study of tlie Subcliiviau Arti-ry in Man
tions is the suprascapular artery arising from the internal mammary artery (see Fig. G). This occurs fi times in 104 cases (practically 12%). Quain " found the same anomaly 4 times in 264 dissections of the subclavian artery (about 1%). Arthur Thomson" found it 9 times in 544 cases (less than 2%). Another anomaly is found in connection with the internal mammary artery. The latter divides into two branches a few cm. from its origin, one of which takes the normal course of the internal mammary artery, while the other follows the anterior axillary line between the ribs and pleura, terminating at the diaphragm in two cases, at the fourth rib in three other cases. This branch is as large as the ordinary internal mammary artery, and. sends branches into the intercostal spaces just as that artery does. This " lateral thoracic artery" is present 5 times in 28 cases (18%) that are carefully worked out. Anatomists mention this anomaly, but consider its occurrence much rarer than our findings indicate. Another important anomaly is observed twice. The anomaly is in the trunks arising from the arch of the aorta. Tb.e first trunk divides immediately at the aorta into the two common carotid arteries. The second trunk is the left subclavian artery. The third trunk is the right subclavian artery. This arises from the distal part of the aortic arch on a level with the fourth thoracic vertebra, and passes posteriorly between the oesophagus and the vertebral column to its usual place on the right side. The right recurrent laryngeal nerve passes directly to its distribution, without looping around tlie subclavian artery. The pneumogastric and phrenic nerves occupy their usual places and relations. This anomaly has been reviewed by Gotthold Holzapfel,*" who collected 200 cases from the literature, including 4 of his own (1 in an animal). He concludes that this anomaly occurs 6 times in every 1000 cases. Quain and other anatomists fixed the ratio at 4:1000. Tiedemann gives the ratio 8:1000, nearly 1%. The middle thyroid artery, " Thyroidea Ima," another anomaly, is found three times. It arises from the innominate artery, and, passing to the median line, supplies the lower lobes of the thyroid gland and the isthmus. Wenzel Gruber " records 125 anomalies of this kind, and concludes that the artery rises most frequently from the innominate artery, Imt also not infrequently comes from the aorta and the common carotid artery. He found it 16 times in 100 consecutive dissections.
" Quain, Commentaries on the Arteries, London, 1844.
" Thomson, Second Report of the Collective Investigation of the Anatomical Society of Great Britain and Ireland. Journal of Anatomy and Physiology, London, Vol. XXVI, p. 78.
"Holzapfel, Anatomische Hefte, XII, I part, p. 373 (1S97).
" Gruber, Virchow's Archiv, Vol. 54, p. 445.
Robert Bennett Bean 317
SUMMARY.
I. The branches of the subclavian artery differ in their origin on the two sides of the body, the most frequent arrangement being similar to Type I on the right side, and Type II on the left side.
(a). The thyroid axis, dividing into the suprascapular, transverse cervical, and inferior thyroid arteries, is not normal, except on the left side.
(b). The transverse cervical artery and the costo-cervical trunk arise from the second part of the subclavian artery more frequently on the right side than on the left side.
(c) The superficial cervical artery is of infrequent occurrence, and is found more often on the right side. See Type I.
(d). The transverse cervical artery terminates by dividing into ascending and descending rami, the latter being commonly called the posterior scapular artery. The former divides underneath the trapezius muscle and supplies the upper and middle part of the back.
(e). There is a tendency in the branches of the subclavian artery to bunch themselves in their origin on the left side, whereas on the right side there is a tendency in each branch to arise directly from the subclavian artery.
II. There are five important, and not infrequent, anomalies to which the attention is directed :
(a) The origin of the right subclavian artery from the descending part of the arch of the aorta. This occurs 4-6-8 times in 1000 cases (0.5% to 1% of all persons).
(b). Variableness in the o]-igin of the transverse cervical artery, especially on the right side.
(c). The presence of a middle thyroid artery (Thyroidea Ima).
(d). The suprascapular artery arising from the internal mammary artery.
(e). The lateral thoracic artery arising from the internal mammary artery.
III. Eighty per cent of the dissections were made in negro subjects, a large number of whom may have been mulattoes or inixed bloods. That hybrids tend toward variation is a recognized biological law. This may explain the unusually large number of abnormalities encountered.
IV. Twenty-three infants were dissected and many of these show irregularities, particularly in the distribution of the suprascapular artery, wliich is frequently deficient, its place being taken by the dorsal scapular arterv.
318 A ('(iiiiposito Study of the Sul)clavi;in Ai'lcrv in ]\lan
V. Tlir liraiulu's of the siil)clavian artery may Ijc inore numerous in
adults than in infants. The l)ranehes rise from all parts of the artery
in adults, whereas in infants the branches frequently rise in a bunch from Part I.
TABLE 1.1
The Orioin of the Arteria IMammaria Interna (Internal Mammary Artery).
Origin. Quain. Bean.
From I'art I 93.3 .806
From Part II ^. 003 .000
From Part III *. 020 .000
From the truncns thyreo-cervicaHs 050 .097
From a common trunk with the A. trans, scap. and the A. trans, colli. .015 .007
From a common trunk with the A. transversa scapuliB 012 .090
TABLE 2.
Showing the Arterie.s that Compo.se the Truncu.s Thyreo-cervicalis (Thyroid Axis) in the Different Types.
Trunous thwen-oprvicaliscnmnnspr! of Type I Type II Type III Type IV Xot iiuncus tnjieo cerMcaiiscomposeaot pig-. 2. Fig-. 3. Fijf. 4 Fig. 5. Classifleil.
A. thyroidea inferior 1 1 1 1
A. transversa colli 1 )
A. transversa scapulae 1 1 j
T. t. c. gives off A. mammaria interna. .0 1
Frequency of each type — Thomson 417 .413 .060 .064 ..044
Frequency of each type — Bean 273 .257 .273 .120 .077
TABLE 3.
The Origin and Anomalies of the A. Thyroidea Inferior (Inferior Thyroid
Artery).
Orig-in. Thomson. Quain. Bean.
As shown in Type I 432 . . . .296
As shown in Type II 430 .900 .277
As shown in Type IV .036 • ... .129
From Part I (alone), as a single branch 095 .101 .287
From the A. carotis communis 001 .003 .000
From the A. thyroidea ima 001 .011 .009
With the A. transversa colli 038 .005 .065
With the A. mammaria interna , ... .046
With the A. vertebralis 005 .001 .027
With the A. occipitalis .018 .009
With the A. cervicalis superflcialis 053 .025 .074
With the A. cervicalis profunda ... .027
Anomalies.
Absent .022 .018
Very large — larger than the A. suhclavia .011 .027
Very small — not supplying the gland .014 .065
One branch to the gland ... .046
Two branches to the gland ... .954
Forming both the A. occipitalis and the A. vertebralis ... .009
1 The figures in the tables are all given in percentages or may be considered as the number of times per thousand by removing the decimal i)oiut.
Eobert Bennett Bean
319
TABLE 4.
The Origin of the A. Cervioalis Ascexdens (Ascending Cervical Artery).
Oiig-iii. Thomsou. Bean.
From the A. tliyroldea inferior 002 .656
Fi'oni the truncus thyreo-cerviealis 030 .099
From the A. transversa colli 022 .091
From the A. cervicalis siiperticialis 038 .077
From Tart I 004 .054
From the A. tranversa scapulae 002 .015
TABLE 5.
The Origin of the A. Transver.sa Scapul.?: (Suprascapular Artery).
Origin. Thomson. Quain. Bean.
From Part I. with other arteries or alone 776 .885 .813
From Part 11. with other arteries or alone 024 .015 .042
From Part III, with other arteries or alone 074 .088 .101
From the A. axillaris 015 .015 .042
From the A. subclavia alone (as a single trunk i 057 .167 .219
With the A. transversa colli . . . .' 080 .080 .118
With the A. mammaria interna 016 .020 .101
With the A. subscapularis .005 .017
Double . 015 . . . .025
TABLE 6.
The Origin of the A. Transversa Colli (Transverse Cervical Artery).
Origin. Thomson. Quain. Bean.
From I'art I, with other arteries or alone 508 .429 .365
From Part IL with other arteries or alone 014 .191 .390
From Part III, with other arteries or alone 477 .380 .245
With the A. transversa scapulae 079 .048 .145
With the A. thyroidea inferior 036 . . . .072
With the A. thoracalis lateralis ... .012
Double 005 . . . .012
TABLE 7.
The Origin of the Ramus Descendens (Posterior Scapular Artery).*
Origin, Deaver. i Thomson. Quain.
From Part I ... .003
From Part II 005 .008 .150
From Part III 023 .508 .353
From the A. transversa colli 968 .484 .480
From the A. axillaris 001
Bean.
.046 .918 .009
TABLE 8.
The Origin of Ramus Ascendens (not Given by Thomson or Quain).
Origin. Bean.
From I'art I 030
From Part II 010
From Part III 030
From the A. transversa colli 730
From the truncus thyreo-cerviealis or its branches 200
' Deaver, Anomalies of the Posterior Scapular Artery, University Medical Magazine, Phila.. Vol. II. p. 151, 1889.
320 A Composite Stmlv of the Subclavian Artery in Man
TABLE 9.
The Origin of the A. Cervicalis Superficialis (Superficial Cervical Artery).
Orig-in. Thomson. Quain. Ucan.
From the A. trausvorsa colli 589 .9G3 .590
From the A. thyroidea inferior 312 .004 .220
From the A. transversa scapulsE 092 .026 .190
From the A. subelavia 002 .008
TABLE 10. The Origin of the A. Intercostalis Suprema (Superior Intercostal Artery*.
OHo-in Quain. Bean.
'^"^"^- Right. Left. Right. Left.
From Part I 086 .220 .030 .075
From Part II 482 .194 .105
From the truncus costo-cervlcalis ... .400 .370
From the A. vertebralis .007 .020
From the A. thyroidea inferior .004
TABLE 11.
The Origin of the A. Cervicalis Profunda (Deep Cervical Artery).
Origin. Quain. Bean.
From the truucus costo-cervicalis .820
From the A. intercostalis suprema 932
From the A. subelavia 049 .130
From the A. thyroidea inferior .040
From the ramus descendens 018 .010
The artery passes :
Above the first rib 936 .820
Below the first rib 064 .180
TABLE 12.
A Comparison of the Most Frequent Origin of the Branches on the Two Sides
OF THE Body.
A rtery.
Right Side.
Origin.
From :
Vertebralis Part I 97
Mammaria interna Part I 95
Truncus thyreo-cervicalis . . . Part I (5 times) 11
Thyroidea inferior Part I 74
Left Side.
Origin.
Transversa scapula? ] Part I
Transversa colli Part II
Ramus asc. A. tr. colli . Ramus desc. A. tr. colli Cervicalis superficialis Cervicalis ascendens Truncus costo-cervicalis Intercostalis suprema . . Cervicalis profunda . . . ,
Part II 66
A. tr. colli 97
A. tr. colli 45
A. thyroidea inferior. . . 70
Part I 78
Tr. costo-cervicalis. ... 86
Tr. costo-cervicalis .... 82
From :
Part I 88
Part I 82
Part I (25 times) 45
Truncus thyreo-cervicalis 45
Truncus thyreo-cervicalis 45
Truncus thyreo-cervicalis 49
Truncus thyreo-cervicalis 80
A. transversa colli 90
A. transversa colli 76
A. thyroidea inferior. . . 70
Part I 100
Tr. costo-cervicalis .... 80
Tr. costo-cervicalis .... 77
Kobcrt Bennett Bean 321
TABLE 13.
compahison of the number of branches from each part of the subclavian Artery on the Two Sides of the Body.
Right. Left.
Part I 80% 83%
Part II 11% 5%
Part III 8% 9%
A. axillaris 2% 3%,
TABLE 14.
The Percentage of Branches fro.m Parts II and III of the Subclavian Arteisv.
Part II. Part III.
Quain. Bean. Quain. Bean.
None 19% 67% 54% 66%
One 67%, > 24% 46% ^ 24%
Two 12% 8% 3% 4%;
Three 9% 7%; 8% 8%
' Quain counted a muscular twig which was not counted in this work.
322 A Composite Study of the Subclavian Artery in Man
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TADLI-: 18. McscLES Slpi-lied by the subclavian Auteuy, with the Branches Supplying Them.
Almost constant.
M . plati/siiKi : f A. cervicalis superficialis. 1 A. cervicalis asceudens.
A. thyroidea inferior.
Frequent ^ ^- transversa scapulae.
A. transversa colli.
Occasional .
Constant J
Frequent.
Occasional.
A. subclavia. Part I. Twigs. 1 Truucus tliyreo-cervicalis. Twigs.
M. trapezius :
R. ascendens transversa colli. Two or more large branches passing between trapezius and rhomboids.
R. descendens transversa colli. Several small branches. Some twigs after passing rhomboids.
A. cervicalis superficialis. Several small branches.
A. transversa scapulae. One large branch just at bend to drop over scapula.
A. cervicalis ascendens. Small branches. A. suliclavia. Small branches.
Constant.
M. rhomboids, and scrratus posienor:
Tr. descendens transversa colli. One large branch under
\ rhomboids (anterior), and several smaller ones into
the muscles. Frequent Jk. ascendens transversa colli from inferior branch be i tween rhomlwids and trapezius.
f^A. cervicalis superficialis. Small branch or branches.
Occasional J A. cervicalis profunda. Small branch or branches.
I A. subclavia. Small branch or branches.
M. levator scapuhv:
{R. ascendens transversa colli. Small branches. R. descendens transversa colli. Small branches. A. cervicalis superficialis. Small branches.
Frequent A. cervicalis ascendens. One large, several small branches.
Occasional A. transversa scapula;. Small branch.
j^are A. cervicalis profunda. Small branch.
M. ser)-atus anterior:
Constant R- descendens transversa colli. Small branches.
Frequent R. ascendens transversa colli. Small branches.
Occasional A. transversa scapulae. Small branches.
M. siipraspinatus:
J A. transversa scapulae. One large branch. \_R. descendens transversa colli. Several small branches.
Occasional A. circumflesa scapulae. One large branch.
Constant.
326 A Composite Study of the Subelavian Artery in ]\laii
AI. infraspinatus:
p (a. transversa scapulii\ One lar;;e branch.
^R. descendeus transversa colli. Several medium branches.
Frequent A. circumflexa scapulae. One large branch.
M. latissimus dorsi:
r^ ^ J. ' fli. descendens transversa colli.
Constant < , , , .
I A. subscapularis.
If. subscaiiularis:
Constant R. descendens transversa colli. ^
Frequent A. transversa scapulae.
M. sternocleido-jnastoidcus:
\ A. transversa scapulae. Small and medium branches.
Constant ^ ji^_ cervicalls superficialis. Small and medium branches.
A. cervicalis ascendens. Small and medium branches.
j Truncus thyreo-cervicalis. Small and medium branches. 1 A. thyroidea inferior. Small and medium branches.
Rare R. descendens transversa colli.
M. omohyoidcus:
^ ^ ^ Ta. cervicalis superficialis, or branches from.
Constant < . ^ ...
[_A. transversa colli.
Frequent A transversa scapulae.
A. thyroidea inferior.
Occasional ^ . . ,. ,
A. cervicalis ascendens.
Rare A. subclavia. Three times.
11. stcrno-hijoidcus, and stcrno-thyroideus :
Constant or frequent A. thyroidea inferior.
Occasional A. transversa scapulae.
Rare A. subclavia.
II. scalenus anterior, nicdius, and posterior:
ex. cervicalis ascendens. Many branches.
Constant J 'i'l'i^ncus costo-cervicalis, or its branches.
A. intercostalis suprema (R. dorsalis). ^A. cervicalis profunda.
„ ,'a. cervicalis superficialis, or branches from.
Frequent. '
I;
A. transversa colli.
Occasional R. ascendens and descendens transversa colli.
Rare A. subclavia.
M. longiis colli: fA. cervicalis ascendens.
Constant. . '. j 'i'l'^'icus costo-cervicalis, or its branches.
I A. intercostalis suprema. La. cervicalis profunda.
Frequent. . A. thyroidea inferior.
Rare .A. sul^clavia.
Robert Bennett Bean
327
CoDstant.
M. hiit!/us capitis: A. cervicalis ascendeus.
Ta. cervicalis profu Constant -j _^ princeps cervici
Frciivient .
Occasional .
Rare.
.1/. siilcniua capitis, and crrricis:
ofunda. Through complexus M. s. Many small hranches.
[n. ascendens transversa colli. Several medium branches i between M. splenii and trapezius.
A. cervicalis superflcialis. Several medium branches between M. splenii and trapezius.
A. cervicalis ascendens. Branch through above fifth vertebra takes the place of A. cervicalis profunda.
J/, semispinalis capitis and lonyissimus capitis {complexus, and trachcio mastoid):
A. cervicalis profunda. Many medium branches beneath
the muscles. A. princeps cervicis. Many medium branches beneath the
muscles. A. vertebralis. Many medium branches Ijeneat'.i the
muscles. R. ascendens transversa colli. Around edge of splenii, or through them. ^A. cervicalis superflcialis. Around edge of splenii, or "^ through them.
A. cervicalis ascendens. Branch through above fifth vertebra takes the place of A. cervicalis profunda.
Constant. ,
Frequent. Occasional Rare
J/, semispinalis cervicis, and longissimus cervicis:
A. cervicalis profunda. Small branches.
Constant -S ^ intercostalis suprema (R. dorsalis).
Frequent R. ascendens transversa colli. Small branches.
Tr. descendens transversa colli. Small branches.
Occasional J A. cervicalis superflcialis. Small branches.
I A. cervicalis ascendens. Small branches.
J/, spinalis cervicis, and iliocostalis cervicis: Constant A. intercostalis suprema (R. dorsalis).
[ R. descendens transversa colli. Small branches. Occasional -| A. cervicalis superflcialis. Small branches.
I A. cervicalis ascendens. Small branches.
J/, mitlti/idtis spina, interspinw, and intertransversw :
Constant.
A. mammaria interna.
A. vertebralis.
.\. cervicalis iirofiinda.
jy. diaphraijnta :
A. mammaria interna.
M. rectus ahdniiiinis:
328 A Composite Study of the SulH-laviaii Artery in Man
Shoulder joint:
[a. transversa scapulae. Constant -j^^^ circumflexa scapulce.
fA. transverfsa colli. Frequent -|^^^ cervicalLs superficialis.
Clavicula: A. transversa scapula?.
Processus acromialis: A. transversa scapulae. A. cervicalis superficialis, or transversa colli.
Stern urn: A. mammaria interna. A. transversa scapulae.
Glandula thijroidea: A. thyroidea inferior.
Glandula mammaria: A. mammaria interna.
ox THE OCCUEliEXCE OF SHEATH CELLS AND THE XATUEE OF THE AXO^^E SHEATHS IX THE CEXTBAL XEEVOUS SYSTEM.
IRVING HARDESTY. {From the Hearst Anatomical Laboratory of the University of California.)
In a previous paper dealing with the development of the neuroglia tissue, a brief note was made of the occasional observance of certain halfmoon or seal-ring cells encircling the medullated nerve fibers of the developing spinal cord of the foetal pig. ^ It was stated that these cells appeared more numerous in the spinal cords of pigs between 16 and 25 centimeters, the period of most active medullation, and that in transverse sections they appear as seal-rings or crescents encircling the medullating axones and that they closely resemble the " nerve corpuscles " or " Schwann's corpuscles " which have been described clasping the medullated fibers of the peripheral nervous system. It was also suggested that, while in the light of recent investigations these cells have probably little or nothing to do with the formation of the myelin of the medullary sheath, they may have to do with the development of the supporting framework of that sheath.
Adamkiewicz, who first described the cells upon the fibers of the developing peripheral nerves, referred to them as " nerve-corpuscles," and -by way of distinction I have referred to the similar cells observed upon the fibers of the central system as " seal-ring cells." This name only applies to their appearance in transverse section and is non-commital as to their particular function.
The purpose of this paper is to give a further description of these sealring cells based upon a more extended study of their occurrence and variations, and to offer a suggestion as to their relation to the medullary sheath. Some attention has necessarily been given to the nature of the supporting framework of the medullar}- sheath.
Material axd Methods.
Pig material has been used almost exclusively in the observations in that the different ages could be easily obtained. All the study has been
American- Journal of Axatomy. — Vol. IV. 26
330 Sheath Cells and A.xoiie Sheaths in the Central Xervous System
made upon the spinal coi'd alone, and usually u\)nn pieces taken from the cervical region. Preparations from the adult liog were compared with similar preparations from the adult human. After some study of younger stages, it appeared that only pigs of about IG centimeters in length and above were necessarily concerned in the study of the structures involved. Prior to this all the fibers of the spinal cord are non-medullated or in the very early stages of medullation and none of the nuclei and their surrounding protoplasm show evidences of the differentiation in mind. The study, therefore, has chiefly involved fcetal pigs of 16, 19, 21 and 28 centimeters, suckling pigs of about two weeks, and the adult.
Both transverse and longitudinal sections were used, supplemented by teased prejsarations. Some of the sections from each specimen were prepared by the Benda neuroglia method as employed by Huber. Others were made from pieces fixed either in Zenker's fluid or Van Gehuchten's mixture and stained lightly with hematoxylin and counterstained -with Congo red. The latter method was employed in that, with other tissues, Congo red is efficient for bringing out cell outlines. Also sections from certain of the stages after medullation has begun and sections from the adult were stained by Mallory's method for wdiite fibrous tissue. Other sections of the adult spinal cord were subjected to the action of pancreatin by the method of " digestion on the slide " described by Flint.
The pieces of spinal cord of different ages from which the teased preparations were made were first split with a sharp razor into thin longitudinal strips about one centimeter long and these were fixed in a mixture of equal parts of saturated aqueous corrosive sublimate and 1 per cent osmic acid. In order to fix the strips straight and extended, they were at first merely immersed in the fluid and then placed in adherence to the walls of the vials containing the fluid with the lower end of each strip alone in the fluid. Corking the vials and allowing the fluid to act for 10 or 15 minutes was found sufficient to stiffen the strips so that they would remain straight and extended when shaken down into the fluid. After doing this they w-ere allowed to remain in the fluid for 12 to 21: hours. The strips were then washed for several hours in water frequently changed.
Especially in the younger stages the closely bundled nerve fibers of the spinal cord are so friable that it was found impossible to satisfactorily dissociate them with even the finest teasing needles. Even after dehydration and while in clearing oil (in wdiich condition nerve fibers usually tease more easily on the slide than when in water and may be mounted in balsam immediately without disturbing their separated positions) but few pieces of isolated fibers could be obtained of sufficient length for satisfactory study. Teasing in glycerine witli needles gave no better
Irving Hardesty 331
results and g]3'cerine mounts aro very inconvenient for work with high power objectives.
After considerable trial, teasing with a lino stream of water was found to give much the best results with the material. The following simple arrangement proved very etlicient: A strip of the fixed tissue was pinned by one end to the middle of a small piece of thin, carefully smoothed wooden board 4 or 5 inches long by 1 inch wide. With the free end of the specimen downward, the board was held in the left hand with its lower end resting at a slight angle upon the bottom of a slender dish of suitable dimensions, while with the right hand a stream of water the size of a fine needle was directed upon the specimen. The bits of dissociated tissue wash down into the stender dish, and a wooden board seems to give less spattering and rebounding of the water than a strip of glass, especially a glass slide with a cell or groove in it. A piece of 8-millimeter glass tubing drawn out to the required capillary dimensions and broken off squarely and the large end thickened and bound securely into a piece of rubber tubing was used in obtaining the sufficiently fine stream of water. This was securely attached either to the tap direct, and the tap water used, or attached to a Woulfe bottle containing distilled water under pressure, the pressure being obtained by attaching the reverse side of the Woulfe apparatus to an air force pump.
With sufficient pressure, a strip of tissue is washed down to a shred in a few minutes. The stream is best directed against it with a slight up and down, brushing motion. After two or three strips have been teased, or until the stender dish is nearly full of water, the dish is set aside and another taken if recpiired. The nerve fibers being stained black by the osraic acid, the stender dish is placed upon a white surface. The material soon settles to the bottom of the stender and the water may be practically all withdrawn. Then the material from several stenders may be all transferred to one smaller stender and again allowed to settle. Then more water may be withdrawn and the material counterstained if desired.
For counterstaining I used 1 per cent aqueous acid fuchsin, which is known to stain osmic material readily and can be easily controlled. It was only desired in the teased preparations to demonstrate the shape and position of the sheath cells. iVfter being in the fuchsin the required time, the material was washed first in 50 jDer cent and then in 70 per cent alcohol. It settles in alcohol more quickly than in water and the alcohol may be drawn off more completely.
Dehydration was completed with 95 per cent alcohol and finally with two changes of absolute. Tlien the absolute was replaced with a clearing
332 Sheath Cells and A\-ono Slioat+is in the fVntrnl Xervons System
oil composed of vqw.xl parts of carbolic acid crystals, xylol and oil of ber<iamot. Xylol alone will clear the material, but it acts more slowly and dries too quickly on the slide where it is necessary to spread out the material before mounting.
To mount, the greater part of the clearing oil was removed from the material settled on the bottom of the dish, and then with the points of fine forceps or with a teasing needle, a sufficient mass of the dissociated fibers were lifted out and placed upon the slide and the surplus oil then drained off or taken up by holding a bit of blotting paper near the mass. A drop of balsam was then added and the fibers gently spread through it. The cover glass placed squarely down upon the mount tends to further spread the fibers out. Thus a preparation is obtained which is permanent and upon which the oil immersion may be used with convenience.
Examination of the preparations shows that teasing with the stream of water results in three advantages not obtained by teasing spinal cord bv the ordinary methods: (1) Bits of nerve fiber are obtained of considerably greater length than could be obtained with needles an,d the fibers are nearly all isolated instead of in compact, broken clumps as often results from needles. (2) The preparation is cleaner. The fibers are washed out, leaving most of the plexuses of blood-vessels and the coarser masses of connective tissue behind in the shred remaining pinned to the wooden board. (3) The fibers themselves are clean. The neu- , roglia fibers and nuclei and the general protoplasmic syncytium otherwise surrounding and adhering to the fibers is washed off, especially from those having acquired a medullary sheath. This adds greatly to the value of the method for the purpose herein, in that almost every nucleus to he seen is adhering closely to a nerve fiber and usually can be considered to represent one of the sheath cells in question.
Of the stains employed upon the sections, the Benda method proved best for the seal-ring cells. The toluidin blue of this method seems to especially differentiate these cells, staining their granular cytoplasm a deeper blue than the general syncytial protoplasm and rendering the cells more easily found than is the case after the more ordinary staining methods. Most of the syncytium is stained light brownish-red by the alizarin of the method, thus giving a background of good contrast. The nuclei and the adult neuroglia fibers when present are, of course, stained a dee|) blue.
In all the figures the camera lucida was used in outlining the drawings and the magnification in each was that obtained with ocular 4 and objective T2 (oil immersion, Zeiss).
Irving Hardesty 333
The Appearance of the Medullary Sheath in the Spinal Cord AND THE Occurrence of the Seal-ring Cells.
Most of the observations upon the origin, development and structure of the sheaths of the nerve fibers have been made upon the fibers of the peripheral nerves. This is perhaps due to the greater ease with which peripheral fibers ma}' be studied. Satisfactory fixation is easily obtained with bits of peripheral Jier-ves, their fibers are more easily isolated, being supported and separated by abundant connective tissue, and they have thicker and stronger supporting sheaths than the fibers of the central system. Indeed, the fibers of the central nervous system are described as having no primitive sheaths, or sheaths of Schwann, at all.
Notwithstanding various conflicting theories, the general concensus with regard to the origin of the nerve axones and their medullary sheaths may be summed up in the following:
1. All axones arise as outgrowths or processes of " nerve cells." *
2. Developing axones become invested by special cells which give rise to the sheath of Schwann but probably have nothing to do with the formation of the myelin of the medullary sheaths.
3. In development, the axone precedes, secondarily the sheath of Schwann appears upon it, and lastly, or simultaneously with the beginning of the sheath of Schwann, the myelin sheath begins to appear.
4. Xo sheath of Schwann and therefore no sheath cells are described for the nerve fibers of the central nervous system. In the peripheral system the sheath cells and therefore the sheaths of Schwann are of mesodermal origin.
5. In the order in which they have been advanced, the theories of the origin of the myelin sheath are: (a) that the myelin is formed through the agency of the sheath cells by a process something like that by which fat is formed by the fat cells (Ranvier) ; (b) that the m5'elin is formed at the expense of the outermost portion of the nerve axone (Kolliker) ; (c) that the myelin is of exogenous origin, formed in the blood and distributed from the blood-vessels to the axones (Wlassak) ; (d) that the myelin arises as the result of influences exerted by the axone upon the surrounding stroma (Bardeen). By "stroma" Bardeen refers to an apparent fluid substance enclosed about the axone by the already formed sheath of Schwann. The theory of Eanvier (supported by Vignal and others) is invalidated by the statement that there are no sheaths of Schwann in the central nervous system, wliile there are medullary
' See Kolliker: Ueber die Entwickelung der Nervenfasern. Anat. Anz., July, 1904, page 7.
334 Sheath Cells and Axoiic Sheaths in the Central Nervous System
sheaths present, and further, hy the conclusion of Gurwitch that for the peripheral nerve fibers the sheath of Schwann has nothing in common with the medullary sheath. It has also been shown by Kolster and Bardeen that the myelin may begin to appear about the axone before the sheath of Schwann is evident, though, as a rule, the axone of the peripheral fiber is enclosed by the sheath of Schwann before the formation cf the myelin is apparent.
6. The medullary sheath is composed of at least two parts, first, the myelin (lecithin, etc.), and second, its su})porting framework. As early as 1862 Mauthner roughly depicted this framework for certain giant fibers of the trout and the coarser portions of it were observed in 1876 by Ewald and Kiihne. who gave it the name " neurol-craiin suggesting it to resemble horn in that they found it to resist the action of certain digestive ferments. Since then it has been studied in greater anatomical detail by various investigators, more recently by Wynn and Ilatai, whose observations were also made upon peripheral nerve fibers.
The seal-ring cells which I have observed in the spinal cord of the pig are somewhat puzzling both as to their origin and their function. In the first place, they appear to have a period of maximum abundance. In the spinal cord of pigs of about 21 centimeters they are more easily found than at any other stage I have examined. In transverse sections stained by the Benda neuroglia method, I have seen as many as three evident in a single field of the oil immersion. While often a field contains none at all, it usually requires but little search to find one, though the nucleus, situated in the thicker side of the ring, may not always be contained in the section. In the older fcetus they seem less abundant, and in the suckling pig it becomes difficult to find them in sections, while in sections of the adult spinal cord satisfactory examples of them are even more seldom found. Their protoplasm seems to have been used up and a free nucleus clasping the side of a nerve fiber nuiy possibly be a neuroglia nucleus instead.
There are no direct indications of seal-ring cells prior to medullation. Xone have been observed upon fibers in the earliest stages of medullation. The conditions before the accumulation of myelin has liegun are represented in Fig. 1, which is taken from the frayed end of a longitudinal section of the future white substance of the cord of a pig of 11 centimeters. The axones (a) appear as well-defined threads much smaller than in the older stages and separated by or imbedded in the general protoplasmic syncytium (.9) which is the early form of the neuroglia tissue, no masses of Avhich show diiferential blue staining l)y the Benda method, nor anv definite outlines indicatinu' individual cells. The
Irvino- Hardestv
535
nuclei at this stage all appear nearly similar and are simply imbedded in the common proto])]asm of the syncytium, the amount about a nucleus depending upon its position.
This study has not involved the spinal cord of the very young stages and. perhaps for that reason, by none of the stains I have employed does the growing axone, Iwfore medullation or at any stage in my preparations, appear as a " group of fibrils," or fibril l)undles, as described by Bardeen for the periplieral nerves and by others cited hy him. The axone of the young spinal cord, at least froui G centimeters np, appears as a nearly homogeneous strand of even calil>er which increases appreciably in size with the growth of the speciuien. At best its structure shows nothing more than a fine, elongated reticulum, the threads of which become heavier and more evident as the fil)er approaches maturity. Though Bardeen's observations were confined to the developing peripheral nerves, my failure to note the filiril-gronp form of the young axone must
Fig. 1. From longitudinal section of white substance of spinal cord of pig of 11 centimeters. Benda method. «= nerve axones; s = syncytium. X 550.
be due to unsuitable methods, or to the fact that I have not examined the very young stages, for it is hardly probable that tlie axone in the central system is essentially difi'erent from the peripheral axone. Also Bardeen states that as early as 2 centimeters, most of the peripheral (intercostal) nerve fil;)ers of the pig are covered with embryonic myelin. This indicates that myelination occurs very much earlier in the peripheral than in the central nervous system of pigs, for not till about IG centimeters have I observed any appearances at all suggestive of the illustrations he gives as representing embryonic myelin.
Fig. 2 represents the frayed end of a clump of axones from the white substance of the spinal cord of a pig of 16 centimeters teased by the water '«*. method. This material was fixed in the corrosive sublimate and osmic acid mixture and the teased fragments stained with acid fuchsin. The appearance of the interaxone substance was verified from sections of the same stage stained by other methods. The teased preparation is
336 Sheath Cells and Axoiie Sheaths in the Central Nervous System
preferable in that the axones, uncut, may be followed a considerable distance and being often washed clean of the interaxonic syncytium, they may be studied more closely. It is seen that even in the pig of 16 centimeters, a stage when the medullation of the peripheral nerves is well advanced, most of the axones of the spinal cord show no signs of medullation, being but slender threads (a) of more or less even contour, with the substance of the syncytium (s) adhering to them.
The fibers indicated by b in Fig. 2 show the appearance of the first stages of the accumulation of myelin, or at least the first stages to be observed after the technic here employed. The myelin begins as small globules of various shapes and sizes adhering to the axone, giving it a beaded appearance. The globules are but very slightly blackened by the osmic acid at this stage and then upon their surface only, making them appear as small blisters which resist the action of the water in teasing. When washed clean of other adherent substance they may be observed minutely and there is no sign whatever of the presence of any other sheath. Between adjacent blisters and connecting them there is usually discerned a thin film on the axone but not always. Usually the globule appears adhering to one side of the axone rather than evenly surrounding it. This form of the first appearance of the myelin upon the axone is similar to that described by Yignal, Westphal, Wlassak, Kolster, Bardeen and others.
Those of the observers who take into consideration the sheath of Schwann of the peripheral fibers, give varying accounts of the time of the appearance of the myelin. After examining the great amount of literature upon the subject, it seems that the sheath of Schwann usually appears upon the peripheral axone before the myelin begins to be deposited, but often simultaneously with its appearance, and sometimes after the appearance of the myelin. The latter sequence indicates that the sheath of Schwann is not concerned in the origin of the m^-elin.
The fiber indicated by c in Fig. 2 is an example of the most advanced stages of myelination to be found in the spinal cord of pigs of 16 centimeters. It is the only fiber found after considerable search through the preparations of this stage which apparently possesses a sheath cell, though the protoplasm of this cell is not distinctly differentiated. There is positively nothing indicating such cells upon fibers of earlier stages of inedullation. In sections of specimens of this age stained by the Benda method I have found no cells distinctly clasping the medullating axone, and showing the definite outline and differential staining of those found in the later stages, and especially in pigs of 21 centimeters. Occasionally a nucleus may be seen upon the side of an axone with protoplasm sur
Irving Hardesty 337
rounding it wliicli is apparently more compact and which stains a deeper blue than the protoplasm of the general syncytium, but instead of having a definite outline the protoplasm seems to grade off into that of the syncytium. This condition is apparent in iiber c of Fig. 2. In general, the nuclei of this stage are merely imbedded in the syncytial protoplasm and show the various types of the neuroglia nuclei.
The appearance of definitely formed seal-ring cells is shown in Fig. 3. In this figure are represented two small areas from transverse sections of the spinal cord of a pig of 21 centimeters stained by the Benda neuroglia method. The cells (c) here show the form suggesting the name given them. Their finely granular protoplasm stains a decidedly deeper blue than that of the now more sparse protoplasm of the general syncyt
FiG. 2. From the spinal cord of a pig of 16 centimeters. Osmic acid and fuchsin. Teased by water. rt = axones before medullation; 6=:axones showing beginning medullation; c= fiber in more advanced stage of medullation and with probable sheath cell; s = syncytial protoplasm. X 550.
ium and their boundaries are definite. The fields were chosen because of each having two cells near together, three of the cells containing nuclei in the section. With the nucleus in the thicker side, the cells usually in this stage completely enclasp the fiber as a ring, but sometimes the protoplasm on the side away from the nucleus is either absent or so thin as to give the appearance of a crescent. Frequently a cell is found of the shape presented in d, where the protoplasm seems mostly extended from one side. In sections, the cells seldom seem to produce a depression in the medullary sheath for tbe fiber usually appears circular. Very probably none of the fibers possessing these cells are full grown, for the cells are found more abundant at about this age and the average diameter of the medullated axones here is much less than that of the adult. At
338 Sheath Cells and Axone Sheaths in tlie Central Nervous System
21 centimeters there are still many fibers in the spinal cord which have not ac(iuired a myelin sheath {a). The syncytial protoplasm is less abundant probably because it is being transformed into neuroglia fibers (n) which begin to appear at this stage.
After birth cells of the seal-ring type are less numerous than in the pig foetus. Fig. 4, c, shows one as found in the suckling pig of two weeks. It is upon a larger fiber than those in Fig. 3 and the protoplasm of the cell is relatively less in amount and merely forms a crescent about the medullary sheath. The nucleus represented by e of this figure is probably a nucleus of a seal-ring cell which has no blue staining protoplasm about it. This is only inferred from its position, resting upon and here slightly indenting the medullary sheath. It may possibly be
c n
p©^
'H •
He
Fig. ;5. Fig. 4.
Fig. 3. Areas from transverse sections of spinal cord of pig of 21 centimeters. Benda method, c and d^ seal-ring cells; a = axones before medullation; n = beginning neuroglia fibers; n« = neuroglia nuclei. X 550.
Fig. 4. From spinal cord of suckling pig of two weeks. Showing stage more advanced than Fig. 2. Otherwise same as Fig. 2. c^ seal-ring cell; e = probably nucleus of former seal-ring cell (taken from a different field); nz= neuroglia fiber; «C:= neuroglia cell. X 550.
one of the larger " free " neuroglia nuclei which has acquired this position. At this stage neuroglia nuclei are sometimes observed which have an area of more compact protoplasm about them and which stains darker than the, now scarce, granular protoplasm of the syncytium. One of these " neuroglia cells " is shown in the figure (nc) and such are described in many of the papers dealing with the neuroglia. Both this and the condition represented in the nucleus e are found in the adult material (see Fig. 7, sc).
In Fig. 5 are arranged some types of fibers selected from teased preparations of the spinal cord of the 31-centimeter pig fixed in the osmic acid mixture and counterstained with fuchsin. Three of these pieces of
Irving Hardesty
339
fiber possess sheath cells and it will be noted that all three are fibers upon which the processes of medullation are well advanced. In the group indicated hy a arc three fibers not separated bv the teasing and there is still present al)out them the syncytial protoplasm and some of the nuclei belonging to it (5). One of the axoncs of this group as yet shows no evidence of myelin, a condition which is quite frequent in pigs of this age. The fibers h and c were selected as showing the next stages in the acquirement of myelin. The medullated fiber with group a was included as illustrating the corrugated or ruffled outline of the growing sheath, an appearance frequently found and which suggests that it is an earlier stage than either of the fibers indicated by c. l)eing a further develop
FiG. 5. Types of nerve fibers selected from teased preparations of spinal cord of a pig of 21 centimeters, showing stages of medullation and nature of seal-ring cells. Osmic acid and corrosive sublimate. Fuchsin. s = syncytium; /"?•=: framework of sheath washed out in teasing; 5C^ seal-ring cells. X 550.
ment of the smaller Idistcrcd or lieadcd form {h and c). The filler d is perhaps in about the same stage, but it is doubtful whether either of the nuclei adhering to it represents sheath cells. The fiber f, showing an even contour of its sheath, is considered as illustrating the type of the most advanced stage in the growth of the medullary sheath found in pigs of 21 centimeters. This type is fairly numerous and often sheath cells are found upon it. The myelin of this type stains more darkly than that of the others, especially that of h and c, where it is much lighter and corresponds with certain of the descriptions of so-called " eml)ryonic myelin."
In the late foetus and in the new-l)orn (suckling pig of two weeks) the conditions more nearlv resemble those of the ailult. j\redullation
340 Sheath Cells and Axoiie Sheaths in the Central Xervous System
has proceeded till there are much fewer fibers of types b and c, Fig. 5. At birth there may be found in the white substance, but very rarely indeed, fibers totally void of myelin such as one of those shown in group a. Sheath cells of the form of the seal-ring cells of the 31-centimeter pig are also more difficult to find in the later stages. This is apparently due to their being relatively less numerous and to the fact that when found they show relatively less protoplasm about their nuclei and about the fibers they clasp.
In the adult especially are unquestionable examples of these cells difficult to find. Usually the protoplasm has apparently been used up or so
Fig. 6. Types of fibers selected from teased preparations ot spinal cord of adult hog. Fixation, etc., same as in Fig. 4. e and ^7 = types of small, thinly medullated fibers from white substance; fr = framework of sheath from which myelin has been washed in teasing; sc = sheath cells (sheath nuclei); p = peripheral sheath, x 5-50.
dispersed that little more than the nucleus remains and the only suggestion that such nuclei do not belong to the general class of the neuroglia nuclei present throughout the inter-axone spaces, is their flattened shape and their position upon the nerve fibers, and, when observed in the teased preparations, the fact that they are not washed off in the process of teasing. It is possible, of course, that during growth neuroglia nuclei proper may be flattened against the medullary sheaths.
In Fig. 6 are presented some of the types of fibers to be found in the
Irving Hardest}' 341
!>pinal cord of the adult hog. They are all selected from teased preparations of the same specimen. Three of these pieces of fiber (a, h and c) possess what may be reasonably considered sheath cells. They were found after considerable search. Sometimes cells could be found adhering to the fibers in the manner similar to that shown upon the fiber d, but these were not considered as examples of the type sought. Cells situated in indentations of the sheath and with a more or less even outer contour were sought as more probable examples of the cell in mind.
There are many fibers in the adult cord relatively larger than the type d, but so far I have found no cells upon their sheaths, which latter are always deeply blackened by the osmic acid. Of the smallest medullated fibers in the adult cord, the types indicated by e and g are interesting. In the peculiar bulbous enlargements of their sheaths and in their relative size, they are identical with certain of the fibers described by Ranvier in the spinal cord of the dog. Ranvier pictured a nucleus with protoplasm about it adhering to what appears to be one of the larger of this type of fibers. So lar I have not found examples of sheath cells upon any of them in the adult hog, but this may be due to the fact that such fibers are much less numerous in the cord than fibers of the larger type and that therefore a much less number of them was examined. Their peculiar appearance can hardly be considered wholly artifact, for the type is quite constant and often one of them may be followed unbroken for several millimeters and throughout shows the same form. It would be difficult to determine whether or not they are younger fibers in the process of mecluUation. They resemble certain of the Remak fibers. The few undoubted collateral branches I have seen in the preparations were of this general type of fiber.
The relation the sheath cells bear to the medullary sheaths of the central nervous system is as much of a question as it is in the peripheral nerves. When, in the study of this question, one examines into the nature of the medullary sheath in the spinal cord, it is immediately evident that it differs from that of the peripheral nerve fibers in several particulars.
While the fiber of the spinal cord is, of course, devoid of any structure similar to the capsule or sheath of Henle possessed by certain peripheral medullated fibers, it also lacks a distinct sheath of Schwann. Many deny that the nerve fiber of the central system possesses anything similar to the sheath of Schwann found on the peripheral filier. Under certain conditions when the myelin is crushed or shrunken away, there may be seen occasionally evidences of a very delicate sheath al^out the periphery of the medullary sheath (/). Fig. 6). jNEore usually, however, such must
'o4'i .Shoalh Cells and A.xono Sheaths in the Central Nervous System
adhere so closely to the myelin as to he invisihle and to break with the breaking- of the myelin sheatb. This thin membrane-like appearant'e was first noted Iiy l\anvier in the cord of the dog and be referred to it as a membrane. It bas since been discussed by Schiefferdccker and others and its existence has been repeatedly denied.
The nerve corpuscles or Schwann's corpuscles of the peripheral nerve fibers are descrilied as lying under the sheath of Schwann — between it and the myelin sheath. The cells here observed upon the fibers of the spinal cord seemingly lie upon the medullary sheath, being attached or in some way in close relation to it, without being enclosed upon it by a perceptible membrane. Sometimes in the teased preparations the protoplasm of the cells seems to blend into the blackened myelin (e, Fig. 5), but in the stained sections the protoplasm appears distinctly outlined from the myelin. The latter is perhaps the true condition, for whatever the function of the cells, the granular, more deeply staining portion probably only represents ' the unti'ansformed endoplasm of the cell. In Fig. 7, sc, is shown one of the seal-ring cells as found in transverse sections of the spinal cord of the adult hog when stained by the Benda method. It is merely a nucleus practically free of endoplasm and its shape and position are the only features which suggest its being one of the cells in question.
I am as yet unable to reach a definite solution of the exact significance of these cells. If one follows them through the preparations with the idea that they are a distinct type of cell, having probably to do with the development of some part of the medullary sheath, the following observations may be made in support of this idea :
1. They do not appear ditferentiated till after the acquisition of myelin has begun.
2. When first indicated they do not appear as definitely outlined and differentiated cells, but rather their more deeply staining protoplasm seems to grade off into that of the general syncytium and to be continuous with it. This, and their being attached to a medullating fiber suggests that they are derived from nuclei and protoplasm formerly a part of the syncytium, and that their differentiation may be due to influences exerted upon it by the developing myelin.
3. During the period in which the process of myelination is at its height, they appear as distinctly differentiated cells with considerable protoplasm (or probably endoj)lasm) about their nuclei, often sulficient to completely encircle the growing sheath at the level of the nucleus.
-i. With the further growth of the medullary sheath, the protoplasm or endoplasm of the cells is apparently used up gradually, till as the sheath
Irving Hardesty 343
nears completion only the nucleus appears adhering to the periphery of the sheath. The fact that even such nuclei are rare in the adult suggests that they also may disappear.
5. In the relative abundance of their protoplasm at the different periods, these cells resemble the nerve corpuscles described for the peripheral nerve fibers and which are interpreted as having to do with the structures of the sheath.
Ox THE Framework of the Medullary Sheaths of the Spinal
Cord.
In none of my preparations of the spinal cord of the hog is there evident any arrangement in the medullary sheaths producing the appearance of the Schmidt-Lantermann clefts and segments described in the sheaths of the peripheral libers. Especially is there no evidence of the heavy, separate interfitting cones described by Wynn. Hatai, who used a method much superior for the purpose to that used by Wynn, describes the structure of the peripheral medullary sheath as consisting of a network which contains the myelin. This " neurokeratin " network consists, he says, first, of two thin layers, one beneath the sheath of Schwann, and the other around the axone, the two being continuous at the nodes of Eanvier ; and second, of a chain of cone-like formations, the bases of the cones being attached to the peripheral layer and the apices to the axone layer. Both the cones and the layers are highly reticular, exhibiting meshes of various sizes and shapes. He thinks the Schmidt-Lantermann clefts are produced artificially.
Hatai found formalin the best fixing agent in his study of this framework. Formalin is the fixing agent required in the Benda method and the alizarin used in the staining procedure of this method apparently brings out the framework of the medullary sheath in greater delicacy of detail than the stain used by Hatai. The toluidin blue of the Benda method stains the axone a dense blue as it does the developed neuroglia fibers, while the white fibrous connective tissue and the framework of the medullary sheaths is stained a light brownish-purple even to the finest fibrillai. After formalin, as after many other fixing agents, the axone shrinks to considerable density and decrease in its normal diameter, but on the other hand, formalin seems to produce a slight swelling of the medullary sheath. In this process the framework of the sheath remains attached to the axone and is thus drawn or distended into a more open condition which renders the study of its detailed structure less difficult.
On comparing sections of peripheral nerve fibers with sections of the
3-i-l: Shoatli Cells nnd Axoiio Sheaths in the (\^ntrnl Xervous System
white suhstanco of the spinal cord, from both of which the myelin has been removed, it is evident at once that, whatever the detailed structure of the sheaths of the two, the framework of the peripheral medullary sheaths is somewhat stronger and heavier than that of the sheaths of the central fiber. This is true for human material and is especially true for the hog. The comparison may usually be made very readily with sections of the spinal cord, for nearly always portions of the ventral and dorsal roots have remained attached to the cord and, involved in the sections, are subjected to the identical technique in staining,' etc., as the cord itself. In the peripheral nerve proper the framework of the medullary sheath is slightly heavier than in the nerve roots close to the pia mater. The nerve roots also do not possess the heavy connective tissue investments of the nerve outside the dura mater. Furthermore, in the hog the framework of the medullary sheath, both in the peripheral and central system, is apparently heavier than in man and the other vertebrates more usually studied. This is coincident with the well-known fact that in the hog the fibrous tissue framework of the organs, especially white fibrous and reticular tissue, is peculiarly abundant.
Under higher magnification the framework of the medullary sheaths of the hog shows a structure and arrangement capable of an interpretation somewhat different from that usually given. The structure certainly differs considerably from that pictured by Wynn. Wynn, however, used the Weigert staining method for medullated fibers and many of the appearances to be obtained by this method suggest that it is somewhat precipitative in its action upon the medullary sheath or that it may be classed among the impregnation methods. Its tendency certainly is to clog the finer structures rather than merely to dye them. Wlassak in his study of the origin of the myelin claims that the Weigert method stains only one substance of the medullary sheath. This substance he calls " cerehriii" and states that it is one of the constituents of the myelin. In this case, as Hatai points out, Wynn pr-obably did not study the real framework of the sheath, the neurokeratin network of Hatai, but rather obtained pictures indicating the distribution of the cerebrin.
As stained by the Benda neuroglia method, the framework of the medullary sheath of the hog spinal cord appears as represented in Fig. 7. This figure contains fibers from both transverse and longitudinal sections of the cord. Each group was taken from an area near the periphery of the section or in the neighborhood of the pia, for the reason that near the periphery the framework appears heavier than toward the center and is always less collapsed and shrunken, due perhaps to better or earlier fixation near the surface of the specimen. It is seen that in transverse
Irving Hardesty 345
sections stained by this method the framework supporting the myelin appears arranged in the form of concentric lamella}. The different lamellae, however, cannot be followed as distinct and individual membranes, for they apparently anastomose with each other and are further connected by still finer threads or branches. The structure is better described as a lamellated reticulum in the meshes of which the myelin is contained. Were it fibrillar in structure, lamellation could not appear in both transverse and longitudinal section. In longitudinal section the meshes of the reticulum appear considerably elongated in the direction of the long axis of the nerve fiber.
At the periphery of the fiber there is a slight condensation of this lamellated reticulum, giving under certain conditions the appearance of a membrane (jj. Figs. G and 7), but close examination of the uncollapsed sections shows this membrane continuous with the more open network further in. This explains the difficulty with which the membrane is seen and the disputes concerning its existence, for consisting of but a condensed peripheral portion of the reticulated framework, the meshes of which are intimately occupied by the myelin throughout, the membrane is really continuous with the framework and therefore necessarily seems to adhere closely to the myelin. The breaking of the medullary sheaths in the fixed preparations consists, of course, of a breaking of the framework, and in the usual osmic "acid and Weigert preparations especially, one could hardly expect to see the apparent membrane except in fortunate cases where the myelin is crushed or shrunken away from the periphery in such a way as to expose it. Quite frequently in the teased corrosive-osmic preparations the broken end of a fiber showed frayed portions of the framework of the sheath as indicated in Figs. 5 and 6, fr. These appearances are due to the myelin having l^een washed out of the meshes of a short extent of the framework by the action of the water in teasing and are prol)al)ly not to be seen except in preparations teased by water.
The lamellated reticulum also usually shows a slight condensation about and upon the axone of tlie medullated fiber. This corresponds to the second thin layer of neurokeratin as described by Hatai. It probably corresponds to the axolemma frequently mentioned in the books. Being of the same nature and formed in the same way as the peripheral membrane, the usual difficulty with which it is seen is perhaps due to the same reason as that given to explain the difficulty with which the peripheral membrane is seen.
In the longitudinal sections of the fibers of the spinal cord it is seen that even the heavier lamella? of the framework do not run uniformly
346 Sheath Colls and Axone Sheaths in the Central Xervous System
parallel with the contour of the liber. At least after the manipulation in making the preparations, lines of adjacent lamellas often appear collapsed upon each other, giving a resemblance of heavier lines running obliquely in the sheath. Often this collapse may be so great as to give openings in the framework, and sometimes, especially nearer the center of my sections of the cord, where fixation is perhaps less perfect, almost the whole framework may appear clotted against the axone or massed, axone and all, at one side of the section of the fiber. A partial collapse of this kind often occurs near the periphery also and gives rise to the
Fig. 7. Small areas from the outer portion of a transverse and of a longitudinal section of the spinal cord of an adult hog. Benda neuroglia method, a ^ axone; aZ = axolemma; p = peripheral membrane; n = neuroglia nucleus; nf ^ neuroglia fibers; sc = seal-ring cell as seen in adult; d=: sheath with collapsed framework. Detail of figure may be better observed with hand lens, x 550.
appearance indicated in fiber d, Fig. 7. Again, in the less collapsed condition, one of the lines of collapse may appear in the longitudinal section to run slantingly from the axone to the periphery of the fiber (c. Fig. 7) suggesting one of the Schmidt-Lantermann clefts of the usual osmic preparations of peripheral fibers.
The framework of the medullary sheaths of the peripheral nerve fibers appears not only somewhat heavier than that of the fibers in the spinal cord, but also its arrangement is more varied and generally more complex. The form of the reticulated framework may be said to consist of
Irving HarJesty 347
two general types with, however, all gradations between the two. In Fig. 8, A and B, there are represented examples of the extremes of the two types. They are chosen from among the dorsal root fibers of the adult specimen and show the nature of the framework as brought out by the Benda stain. The majority of the fibers in both the nerve roots show an arrangement of the framework conforming in various degrees to type A. The framework of type B, though somewhat heavier in structure, conforms quite closely with the general type found in the spinal cord. To illustrate type B, a piece of fiber involving a node of Ranvier (nR) was chosen to show the interesting fact that the lamellated reticulum of the sheath framework is not interrupted at the node. Not only are both
J5
c ai
-iC^^S.
Fig. 8. Transverse and longitudinal sections of dorsal root (peripheral) nerve fibers from same preparations as Fig. 7. Showing extremes (A and B) of the two general types of framework of medullary sheaths, sch = sheath of Schwann; «^ nerve corpuscle; ni^^node of Ranvier; c = cone arrangements of framework; other letters =: same as in Fig. 7. Use hand lens to observe details cited, x 550.
the outer and inner " membranes " continuous through the node, as pointed out by Hatai, but also some of the intermediate lamella) pass from one internode to the other. From the fact that but slight condensation is apparent at the nodal constriction, it is probable that the framework is less abundant at that point. Close examination shows that the reticulum suddenly narrows clown by both a diminution in the number of its lamellae and a diminution in the size of its meshes. The same general behavior is also apparent at the nodes in fibers of type A.
Sheath frameworks of the type B seem less frequent in the peripheral nerves proper than in the nerve roots within the dura mater. So far, however, I have examined sections of only one piece of peripheral nerve
348 fShcatli (V'lls and Axouu Slicaths in tlie Central Xervous System
stained by the Bend a method. The root fibers were chosen for the illustrations because, being on the same slides as the sections of the spinal cord, they were subjected to the identical fixation, treatment and decolorization as the fibers in the cord, and were therefore deemed better for comparison with the conditions found in the cord.
The form of sheath framework shown in A, Fig. 8, is no doubt the form to which attention has been usually given in the literature. In this the reticulated framework is more or less condensed into interfitting conical partitions between masses of less intimately supported myelin. In this condensation the outer and inner " membranes " (p and cil) are maintained and rendered even more evident. The partitions when in the form of cones are so arranged that the bases of the cones are continuous with the peripheral membrane and the apices with the axolemma. This is necessarily the case. Otherwise they would not be conical. When a sheath shows the decided conical arrangement for any considerable distance, which it very seldom does, the cones are not necessarily arranged ])arallel and interfitting throughout the distance. For a short extent tliey may be parallel, then irregular cones may be interposed or cones with their apices pointing in opposite directions. The most perfectly formed cones themselves contain openings of the same optical properties as the spaces between the cones. As stained here the cones appear to consist of a fibrillated reticulum with the meshes greatly elongated in the direction occupied by the cone between the axone and the periphe^3^ In A, a fiber was found through which the knife passed obliquely at a region of more or less perfectly formed cones. This allows a certain amount of perspective. Luckily the region also possessed a sheath nucleus. It is here especially evident that the cones do not fit cleanly upon the axone but are continuous witli the axolemma both above and below by a more irregularly dispersed portion of the reticulum in such a way as to give an appearan-ce resembling an open umbrella, the rib-braces of which often extend to the apex of the adjacent cone (c. Fig. 8). The appearance shown in the transverse section indicated by A is frequently seen in the sections of peripheral fibers and is interpreted as a section involving the base of one cone and the apex of another. The heavier fibrillse show a peculiar whirled arrangement which is probably due to the lamellae of both cones being cut at levels where they are curving upon the axone in the one case and the periphery in the other.
Though frec[uently cones are to be found in the hog material somewhat longer than the example chosen in .1^ I have as yet seen none as long as certain of the cones pictured by Hatai and Wynn for the peripheral nerves of the animals thev studied. The finelv fibrillated reticular nature of
Irving Hardesty 349
the framework suggests tliat the heavy cones pictnred by Wynn may after all refer to the arrangement pictured here. His pictures probably represent the conical arrangement of the reticulated framework, the fine meshes of which had been clogged by the precipitate of the Weigert method.
The Schmidt-Lanterinann clefts seen in the usual osmic preparations of the peripheral nerves are interpreted as representing the cones in longitudinal section. The cones, being condensed portions of the framework, W'hich for that reason contain less myelin than other portions of the sheath, are therefore less blackened by the osmic acid. Light passing through them more readily results in the familiar appearances.
As is well known, in the ordinarily fixed material, every peripheral fiber does not show the clefts, and when they are shown they seldom appear in straight, even course slanting from the axone to the periphery. Further, the clefts never appear parallel along a considerable extent of a fiber, indicating that the cones do not all lie in the same direction. Again, it is invariably claimed that the clefts are not present in the fresh condition of the medullary sheath; that after death the sheath soon undergoes changes resulting in their appearance.
i\.ll the statements concerning cones and clefts in the medullary sheaths have been made with reference to the peripheral nerve fibers alone. I have found neither in the fibers of the spinal cord. In the peripheral fibers it seems to me that a partial explanation of the cones is suggested in the many varieties of arrangement of the framework of sheath to be found in the fixed and stained material. Considering types A and B of Fig. 8 as the two extremes, a study and arrangement in series of the intermediate forms may be made which will suggest that the intermediate forms are gradations from type B into type A; in other words, that the form of framework shown in type B, though less frequent in the preparations, may represent more nearly the normal arrangement and that type A is probably derived from type B through a procession of post-mortem changes. In the intermediate forms may be noted: (1) those in which the lamellated reticulum of type B, arranged more or less parallel with the axone, contains occasional small, oval or globular spaces interrupting the parallel arrangement; (2) tliose in which the spaces are more numerous, some of them much larger than others and so shaped and situated with reference to each other as to suggest that the larger spaces arise from a coalescence of the smaller; (3) those sheaths in wliich the larger spaces predominate, giving the framework a marked blistered or honeycombed appearance with the smaller spaces in the partitions between the larger; and finally, those which conform in
350 Sheath Cells and Axoiie Sheaths in the Central Xervous System
general to type A of Fig. 8. Here a continued coalescence of the spaces has resulted in some so large that they more or less completely encircle the axone and are hounded by necessarily condensed portions of the reticulated framework which, at the periphery of the sheath and about the axone, amount to little more than the outer and inner layers of Hatai. The partitions between adjacent large spaces themselves often contain numerous smaller spaces. These larger spaces encircling the axone may be often so shaped and arranged that in longitudinal section, either optically or by the microtome, the resulting partitions of the framework between them may easily appear in the more or less conical form. In the left-hand end of the bit of fiber indicated by A, the cones are less apparent than further to the right. Many of the fibers with numerous larger spaces do not show the conical arrangement of the framework, even as distinctly as is indicated in .^4.
The spaces are interpreted as occupied by globules of myelin, the larger resulting from a coalescence or fusion of the smaller globules. In the normal fresh condition the myelin is probably not in the form of globules at all but as a more finely divided emulsion evenly distributed throughout the framework supporting it. Globulation, beginning as very small globules which later coalesce into the larger, apparently results in a distortion of the natural arrangement of the framework of the myelin sheath. The beginnings of such may be noted even in B of Fig. 8 and in all fibers of its type. In accordance with this view the conical arrangement of the framework and all the intermediate forms may be looked upon as artifacts. The material of my preparations was taken at the slaughter house shortly after death and immediately placed into the fixing fluid. That the peripheral nerves were more exposed to the atmosphere and to handling probably explains why globulation is so marked in their fibers and not in those of the spinal cord. However, the material of my Brenda preparations of the human cord was taken 48 hours after death and in this also the sheaths of the central fibers do not show the conical arrangement of the framework. But it also was placed into the fixing fluid immediately upon removal from the body.
That the medullated sheaths of the peripheral nerve fillers after fixation in weak solutions of osmic acid or after poor osmic fixation usually present the appearance of a coarse network, is a matter of frequent observation. Lantermann himself noted such an appearance. Ewald and Kiihne named it neurol'eratin. The appearance is consider(3d due to the myelin being in the form of imperfectly blackened globules, the interstices between the globules giving a merely optical impression of a network. Pertik, however, interpreted it as indicating the presence
Irving Ilardesty 351
of a substance between the globules which colored differently by the osmic acid. Boveri and Kupft'er thought the appearance of the network to result from a stage of the decomposition of the myelin, while on the other hand, Gedoelst affirmed the preformation and preexistence of the network, agreeing with Pertik that it indicated the presence of two substances in the myelin sheath. i\Iore recently (1904) Chio, experimenting with different solutions of osmic acid upon the peripheral fibers of the frog and guinea-pig, reached the conclusion that the globules are a constant form of the myelin. He finds globules present not only after the action of the osmic acid but after various other reagents as well, both isotonic and anisotonic. His illustrations, all of them after the action of osmic acid, present the appearances usually found in imperfectly blackened medullated fibers. By removing the blackened portions, the globules of myelin, from his pictures, all of them may be homologized with the form here indicated by A in Fig. 8 and with the gradation forms between A and type B.
Without doubt myelin exists normally in a finely divided form — an emulsion. For this reason the nerves possessing it appear white by reflected light. In the fresh condition, however, the individual droplets are much smaller than after post-mortem exposure and treatment with reagents. The larger globules, arising after death by a continual coalescence of the smaller, perhaps bear a similar relation to the condition in the fresh nerve as do the globules of cream bear to those of fresh milk. In the finely divided condition the myelin is distributed evenly throughout the sheath framework supporting it ; in the coarser globular form the normal arrangement of the framework is distorted in the characteristic manner by the continued coalescence of the smaller into the larger globules, the conical appearances resulting from the necessary shape of the large globules within the confines of the cylindrical sheath.
In the central system there is no sheath of Schwann conforming to the distinctly formed membrane investing the fibers of the peripheral system. In my sections the sheath of Schwann of the peripheral fibers is well differentiated by the Benda stain. It seems everywhere to be com]:)letely separate and distinct from the framework of the sheath, as is shown in Fig. 8, sch. The sheath nuclei, usually pictured as adhering to the sheath of Schwann, by no means necessarily do so. Usually surrounded by a small amount of protoplasm, they may as often be found adhering to the surface of the medullary sheath as to the inner surface of the sheath of Schwann. The sheath of Schwann closely investing the medullary sheath, the nuclei are usually in contact with both.
The sheath of Schwann in both structure and staining properties resembles the ordinary basement membranes of the epithelia of the body.
353 Sheath Colls and Axoue Sheaths in the Central Xervous System
Basement membranes are of connective tissue origin and are not cellular. The sheath nuclei may represent certain of the cells having to do with the development of the sheath of Schwann which were enclosed within the sheath and therefore separated from the similar nuclei distributed in the endoneurium outside the sheath. It is well known that, while an internode of the medullated peripheral fiber usually has a sheath nucleus, one is not present in every case, and further, a single internode may sometimes show two or more sheath nuclei.
On the other hand the sheath nuclei may have to do with the development of the framework of the myelin sheath as well as with the sheath of Schwann. The framework, both of the central and peripheral fibers, stains like the sheath of Schwann. It is suggested that the seal-ring cells of the foetus and the sheath nuclei of the adult spinal cord represent " cells " derived from the syncytium and whose activities result in the reticulated framework of the medullary sheath ; that, wherever found, the protoplasm about the nucleus represents only the endoplasm which is being transformed into exoplasm, which in its turn is transformed into the lamellated reticulum by a process similar to that described by Mall in the development of the fibrous connective tissues ; and finally, that the origin of the framework and the origin of the sheath of Schwann of the peripheral fibers may be similar.
The framework of the medullary sheath in the spinal cord resists the digestive action of pancreatin as first noted by Ewald and Kiihne for that of the peripheral fiber. However, in the digested sections it does not appear so abundant as after the Benda neuroglia stain. After fixation in other fluids it does not appear as abundant as it does after fixation with formalin and also it stains very lightly or not at all by the ordinary staining methods. IMallory's method for white fibrous connective tissue stains it but lightly. The digested sections of the spinai cord stained by this method or with strong fuchsin solutions show more or less collapsed circles representing the transversely cut nerve fibers. These circles contain remnants of the framework usually so collapsed and washed together that little semblance of the original arrangement can be made out. Occasionally there is a small inner ring showing the opening from which the axone has been digested and representing the inner layer of the framework or axolemma with certain other portions of the framework collapsed upon it. The outer ring, representing the periphery of the fiber, is better maintained, due probably to the presence of the inter* stitial framework of the white fibrous connective tissue of the spinal cord.
Irving Hardesty 353
Summary.
1. There are present upon the medullated fibers of the spinal cord cells similar to the nerve corpuscles or sheath cells of the peripheral nerve fibers.
2. These cells are more abundant and possess more protoplasm during the period of the most active formation of the myelin sheath than during the later stages.
3. They do not appear upon the fibers till after the fibers have begun to acquire myelin.
4. They are apparently derived from the nuclei and protoplasm of the syncytium of the developing spinal cord and are perhaps difi:erentiated through some influence exerted upon the syncytium by the developing myelin upon the axones.
5. These cells occur much more rarely upon the adult fibers and when found possess little or no protoplasm.
6. The framework of the medullary sheaths of the spinal cord occurs in the form of a lamellated reticulum in the meshes of which the myelin is supported.
7. This framework difl'ers from that of the medullary sheaths of the peripheral nerve fibers in that it is not quite so heavy and always shows an arrangement parallel with the axone of the fiber.
8. The more or less parallel arrangement of the reticulum Is probably the normal condition of the framework in the peripheral nerves also, the post-mortem appearance of the usually described coarse " neurokeratin network " being but a distortion of the normal arrangement produced by a continued coalescence of the much finer globules of the original myelin emulsion, the occasional conical arrangement of the framework representing the final result of the further coalescence of the globules.
9. The framework of the medullary sheaths of the spinal cord resists digestion as does that of the medullary sheaths of the peripheral nerves.
10. While there is a supporting contingent of white fibrous tissue among the nerve fibers of the spinal cord, the statement is confirmed that there is no distinct, separate membrane investing the fibers of the central system corresponding to the sheath of Schwann investing the medullated fibers of the peripheral nerves.
11. The sheath cells of the spinal cord are probably concerned in the development of the framework of the medullary sheath and probably in a manner similar to that in which the other fibrous supporting tissues of the body are developed.
354 Sheath Cells and Axone Sheaths in the Central Nervous System
AUTHORS CITED. Adamkiewicz, Albert. — Die Nervenkorperchen. Ein neuer, bisher unbekannt er morphologischer Bestandtheil der peripherischen Nerven. Sitzb.
der Kais. Akad. der Wiss. (Wien), Bd. XCI, Abth. Ill, I6s5. Bardeex, C. R. — The Growth and Histogenesis of the Cerebro-spinal nerves
in mammals. Am. Jour. Anat., Vol. II, No. 2, 1903. BovERi und KuPFFER. — Ueber die Ban der Nervenfasern. Sitzungsbr. der Ge sellsch. fur Morphol. und Physiol. (Munich), Bd. I, 1885. Chio, M. — Sur quelques particularites de structure de la fibre nerveuse
myelinique soumise a Taction de I'acide osmique. Arch. Ital. de Biol.,
T. XLI, Fasc. 2, 1904. EwALD und KIJHNE. — Ueber einen neuen Bestandtheil des Nervensystem.
Verhand. des naturh. med. Vereins zu Heidelberg, Vol. I, Heft. 5,
1876. Flixt, J. M. — A New Method for the Demonstration of the Framework of
Organs. The Johns Hopkins Bulletin, Vol. XII, 1902. Gedoelst. — Etude sur le constitution cellulaire de la fibre nerveuse. La
Cellule, T. Ill, Fasc. 1, 1886. GuRWiTSCH, A. — Die Histogenese der Schwannischen Scheide. Arch, fiir Anat.
und Physiol., Anat. Abthl., 1900. Hardesty, I. — On the Development and Nature of the Neuroglia. Am. Jour.
Anat., Vol. Ill, No. 3, 1904. Hatai, S. — The Neurokeratin in the Medullary Sheaths of the Peripheral
Nerves of Mammals. Jour. Comp. Neurology, Vol. XIII, No. 2, 1903. HuBER, G. C. — Studies on the Neuroglia. Am. Jour. Anat., Vol. I, No. 1, 1901. KoLSTER, R. — Beitrage zur Kenntniss der Histogenese der peripherischen
Nerven, etc. Beitrage zur path. Anat., XXVI, 1899. KoLLiKER, A. vox. — Ueber die Entwickelung der Nervenfasern. Anat. Anz.
Bd. XXV, 1904. Lantermanx, a. J. — Ueber den feineren Bau der Markhaltigen Nervenfasern.
Arch, fiir Mikros. Anat., Bd. XIII, 1877. Mall, F. P. — On the Development of the Connective Tissues from the Connective Tissue Syncytium. Am. Jour. Anat., Vol. I, No. 3, 1902. Mauthner, L. — Beitrage zur naheren Kenntniss der morphologischen Ele mente des Nervensystems. Kais.-Konigl. Hof- und Staats-druckerei,
1862. Pertik, O. — Untersuchungen iiber Nervenfasern. Arch, fiir Mikros. Anat.
Bd. XIX, 1881. Raxvier, L. — Traite Technique D'Histologie, 1889, p. 814. Schiefferdecker, p. — Beitrage zur Kenntniss der Nervenfasern. Arch, fiir
Mikros. Anat., Bd. XXX, 1887. Westphal, a. — Ueber die Markscheidenbildung der Gehirnnerven des Men schen. Arch, fiir Psychiatrie., Bd. XXIX, 1898. Wlassak, R. — Die Herkunft des Myelins. Arch, fiir Entwickl.-mech., Bd. VI,
1898. Wynn, W. H. — The Minute Structure of the Medullary Sheath of Nerve Fibers.
Jour. Anat. and Physiol., Vol. XIV (N. S.), 1900. ViGXAL, W. — Memoire sur le developpement des tubes nerveux chex les
embryons des Mammiferes. Archives de Physiologie, XV, 1883.
The Development Of The Lymphatic Nodes In The Pig And Their Relation To The Lymph Hearts
Sabin FR. On the Development of Lymphatic Nodes in the Pig and their relation to the Lymph Hearts. (1905) Amer. J Anat. 4: 355-390.
By
Florence R. Sabin. From the Anatomical Laboratory, Johns Hopkins University.
With 17 Text Figures.
Notwithstanding the numerous investigations on the lymphatic nodes, there are many points in regard to their structure and development in which our knowledge is not yet clear.' For example, such a fundamental question as the relation of the nodes to the lymphatic system as a whole and to the vascular system, in other words, the prohlem of general morphology: or, more special questions in regard to the nodes themselves; primarily the existence of a structural unit; and secondarily the relations of the endothelium of the channels to the reticulum within the node, whether the channels are open or closed, and the origin of the lymphocytes.
In regard to the problem of general morphology, we have previously shown " that the lymphatics are modified veins. They develop as bloodvessels do, by the budding of endothelial cells, and the direction of their growth is determined by the arteries and veins. In the lymphatic system there develop four lymph hearts which pulsate in the amphibia; but in the mammalian forms, at least in pig and human embryos, have no muscle in their walls. These lymph hearts drain the body, that is to say all the lymph passes through them before entering the veins. It will be shown in the present paper that the first lymph nodes in the body develop from the lymph hearts. That is, the organ which was a pulsat ^ During the past eleven years, there have been four extensive researches on the development of lymph nodes by Gulland, Saxer, Retterer, and Kling. Each of these authors has reviewed the literature. Gulland, Journal of Pathology and Bacteriology, Vol. 2, 1894; Saxer, Anatomische Hefte, Bd. VI, 1896 Retterer, Journal de L' Anatomie et de La Physiologie, 1901 Kling, Upsala Lakareforenings Forhandlinger, 1903, and Archiv f. mik. Anat. u. Entwicklungsgeschichte, Bd. 63, 1904.
^Sabin: American Journal of Anatomy, Vol. I, 1902. American" .Tocrnal of Anatomy. — Vol. IV.
356 Developiiiont of tlie Lyniphatie Xoilos in the Pig
ing heart in the aniphil)ia becomes transformed into a node in the higlier forms. The lym])li heart is the point from which ducts radiate in development to drain a large area, generally speaking a quarter of the surface of the body, and here the primary lymph node develops. Subsequently there are secondary points, from which ducts growing from the Ivmph heart radiate to drain lesser areas, and here other nodes are formed. These are subcenters through which lymph passes before reaching the primary node.
As to the nodes themselves, the study of their development Ijrings out that they are made of two fundamental structural elements. First, a lymphoid or adenoid tissue, consisting of lymphocytes in a reticulum around the blood-vessels making the lymph cords and germ centers; and secondly a lymphatic tissue, or sinus, made of large numbers of lymph ducts closely packed together. In brief, an ordinary lymph node is a blood vascular organ, made in part of structures derived from the bloodvessels and in part of structures derived from the lymphatics. The vascular unit of the node is the terminal artery and its capillary plexus, the artery being bordered by the cord and the capillary tuft surrounded by the germ center. These two elements, the vascular and the lymphatic, are found in varying proportions in the ordinary node. However, both in the embryo and in the adult, either element may be found alone. In the emliryo and probably in the adult pig, there are small lymph follicles consisting of a tuft of blood papillaries surrounded by lymphocytes and entirely without a sinus. In the hfemolymph node and in the spleen the same type of lymphoid tissue is found, but here the sinuses are made, not of lymph ducts, but of veins. Thus in the blood vascular organs the lymphoid element consisting of lymphocytes in the adventitia of an artery is constant, while the sinus element varies, being absent, or made of veins, or of the modified veins wdiich are called lymphatics.
Throughout the paper certain terms have been adopted. Lymph node is used as a general name to cover all lymphatic glands; the term follicle is used to represent a simple node consisting of the structures that go with a single artery. The simplest node consists of one follicle; other nodes are groups of follicles. The follicle is the anatomical or structural, unit; it is also the vascular unit. The follicle may be without a sinus, or surrounded by a lymphatic sinus or surrounded by a venous sinus.
The term lymph heart has been retained notwithstanding that in the pig there is no muscle in its wall at any stage. It is, however, a sac from which all the ducts for the skin radiate and in that sense is homologous with the lymph heart of the amphibia.
Florence E. Sabin 357
Material and methods. — The material for the present study has been embryo pigs of all stages. In studying the development of the nodes, just as in studying the development of the ducts, it is essential to employ injections, both lymphatic and arterial, and these injections have been made in every stage. The lymphatics have been injected by means of a hypodermic syringe, with either saturated aqueous Prussian blue or with India ink. The material has been preserved for the most part by the injection of a saturated solution of bichloride of mercury, either into the aorta or into the umbilical vein. The blood-vessels are usually first washed out with warm salt solution, then the bichloride introduced and continued until the embryo is hard and white. The injection is made slowly with a pressure of about 100 mm. of mercury and the bichloride allowed to stay in the vessels from one-half to two hours. It is then washed out thoroughly by injecting 70 per cent alcohol through the same canula. The embryo is then placed in 80 per cent alcohol over night and the next day transferred to 95 per cent alcohol. This method involves the least possible shrinkage, indeed it may be made to produce a slight distension of the tissues, which is an especial aid in studying lymphatic nodes.^
In studying the developing nodes in fresh tissue, it is readily noticed that they ^are sometimes found distended with fluid and sometimes collapsed. It is just as easy to tell with the unaided eye when a node is thus distended with lymph as to distinguish between the mesenteric lymph nodes distended with chyle or collapsed and empty. This method of injection produces the same distension of the spaces that occurs normally when the node is in active function; that is to say, it makes the lymphatic ducts rounded rather than collapsed. This explains the especial value of the method as applied to lymphatic tissue.
A valuable aid in the localization of the nodes, and especially in studying the relations of the lymph hearts to the developing nodes, is found bv making injected embryos transparent.' The lymphatics are first injected with India ink and then the entire embryo is placed in 95 per cent alcohol. They are left in the alcohol until they are shrivelled. This takes at least two weeks. The embryos are then cleared in a dilute solution of potash from 1 to 2 per cent, taking from 1 to 4 hours. The specimens are preserved in glycerine, at first 20 per cent and later in pure glycerine.
^ McFarland : Jour, of App. Microscopy, Vol. II, No. 10, and Myers, Ibid., Vol. VI, No. 12, and J. H. Bull., 1905.
■* Mall: American Journal of Anatomy, Vol. IV, 1905, p. 6.
358
Developineut of the Lymphatic Nodes in the Pig
The hjmpli heart. — The present paper is a continuation of two papers previously presented in this journal, the first in Vol. I, 1901, and the second in Vol. Ill, 190-1. It has been shown ^ that the lymphatics bud off from the veins at the root of the neck, grow along the internal jugular vein on either side, and expand into a sac in the neck. This sac or lymph heart is shown in Fig. 1 as it appears in the neck of a pig 2.7 cm. long.
hecn-t
Fig. 1. Embryo pig, 2.7 cm. long, showing the anterior lymph heart injected. X about 41/1-. E, extravasation at the point of injection; Id, lymph ducts leading from the extravasation to the lymph heart.
The lymphatics were injected with India ink by a hypodermic needle introduced into the ducts over the shoulder at the point marked by the extravasation in the figure. The relation of this sac to the veins is shown in the accompanying diagram. Fig. 2. One duct of the sac liesalong the course of the internal jugular vein. Just below the ear, under cover of the sterno-cleido-mastoid muscle, this duct widens into a sac which makes an arch in the neck. The sac curves outward and down
Ibid., Vol. I.
Florence E. Sabin 359
ward with the apex, marked a in the diagram, near the surface, adjacent to a superficial vein over the shoukler. This apex is to be found in the triangle between the sterno-cleido-mastoid muscle and the trapezius. From the apex of the sac, a duct follows along the vein of the shoulder and empties into the duct along the internal jugular vein. This duct becomes the main duct of the sac.
Figure 3 is a section of the base of the sac at about the level marked b in Fig. 2. The section is cut transversely through the neck of a pig 2 cm. long and passes through the larynx. It shows the relation of the lymph heart both to the internal jugular vein and to the sterno-cleidomastoid muscle. The lining of the sac consists of a single layer of endothelium.
Fig. 1, which shows the lymph heart and its ducts in a pig 2.7 cm. long, is to be compared with Figs. 1 and 3 in this journal, Vol. Ill, 1904, pp. 184 and 185, which show the superficial lymphatics in pigs 2.5 cm. and 3 cm. long.
From these three figures it can be seen that the lymph ducts or capillaries grow
J, ,, " J, ,, n , , ii 1 • I'lG- 2. Diagram showing- the
irom the apex Ot the sac first to the Skm relation of the lymph heart, of
of the shoulder and back of the head. Then hea'rt'is in soiid^bfacii. '!i,^apex
-, , „ -, p ., „ ,, of the lymph heart: b, base of
ducts grow forward from the apex ot the sac the lymph heart; ejv, external
, , .. I? , 1 , 1 ■ T . • 1 jugular vein : /i\ facial vein ;
over the surface of the sterno-cleido-mastoid O'l', internal jugular vein, muscle, and form a long plexus around the
external jugular vein parallel to the anterior border of the muscle. This plexus is shown in a little later stage in Fig. 6, and in section in Fig. 5. From this long plexus ducts first grow to the face as is shown in Fig. 2, Vol. Ill, p. 185. Later on it will be shown that at this stage, namely, when the pig is 3 cm. long, the apex of the sac begins to be transforined into a lymph node.
The condition of the lymphatic system in the neck of a pig 3 cm. long is as follows: There is first the lymph heart with its efterent ducts connected with the veins; then ducts have grown from the apex of the sac first to the skin of the shoulder and back of the head, and secondly to the face. The sac shows also the first rudiments of a lymph gland.
The maximum size of the lymph heart is attained when the pig is 3.6 cm. long, and in Fig. 4 is given a flat reconstruction of the sac at this stage. It was made from a set of serial sections and gives the size more accurately than the potash specimens. Fig. 5 is a section from the
360
Development of the Lymphatic Nodes in the Pig
same series taken at the level marked h on Fig. 4. Tt corresponds with Fig. 3, and shows a similar relation to the internal jugular vein and the sterno-cleido-nuistoid muscle. It shows that the sac comes nearest the surface between that muscle and the trapezius. It also shows the external jugular vein at the anterior border of the sterno-cleido-mastoid muscle and the neighboring plexus of lymph ducts. A section about half way between the letters a and h on Fig. 4 shows the heart near the surface and the duct adjacent to the vein as two distinct cavities.
\ K^^^h'W^W^
>::iP^
t o
Keart
scm
d/
L snvn
/
Fig. 3. Transverse section through the neck of an embryo pig, 2 cm. long, showing the anterior lymph hearts, x 15. Ijv. internal jugular vein; I, larynx; p. pharynx; son, storno-cleido-mastoid muscle; sh, sympathetic nerve; rn. vagus nerve.
Fig. G is aiiotlier specimen made transparent in potash. It is from a pig 6 cm. ](Mig and is to 1)0 compared with Fig. 5, Vol. Ill, p. 188, which is from a pig 5.5 cm. long. The former shows the lymjDhatics in the depth and tlie latter those of the surface at al)0ut the same stage. The injection for this specimen was made in two places: one just back of the fore leg as marked by the extravasation ; from this injection the ducts over the shoulder, the lymph sac, and two lapge ducts running to the long plexus were filled. The second injection was made l)etween the eye
Florence E. Sabin
361
. and ear, by which the capiHaries over the face and the long plexus in the neck were filled.
In Fig'. G the lymph heart is still plain, showing as a triangle in the depth. It has modified somewhat in shape, inasmuch as lymph nodes are forming at the apex and base, making the angles of the triangle appear as knobs. The apex of the sac is now labeled primary lymph node, and the base is lettered h. The actual size of the triangle as a whole is not greater than when the embryo was 3.6 cm. long. That is to say, the distance from the apex to the base is about 4 mm. in either case.
The ducts over the shoulder from the apex of the sac are well injected, these being the first set to develop. The set of ducts which grows forward from the apex of the sac over the surface of the sterno-cleidomastoid muscle to make the long plexus in the neck shows somewhat, but is not as well injected in this specimen as in Fig. 7. They are present at this stage but the injection from the region near the eye was not pushed quite far enough to bring them out well. This set of ducts develops into the long and abundant plexus which follows the course of the external jugular vein as it lies parallel to the sterno-cleido-mastoid muscle. From this long plexus, the entire face, front of the neck, fore leg, and thorax are supplied with lymphatics, and these different sets can be seen in Fig. 6. All of these sets of ducts anastomose in the skin, as can be seen in Fig. 5, Vol. Ill, p. 188.
In brief, the ducts for the shoulder and back of the head grow directly from the lymph heart; those for the face, neck, and fore leg grow from the lymph sac, but form a long plexus along tlie external jugular vein before reaching the skin. As has just been said, both sets of ducts, distinct in the depth, anastomose in the surface. The line of growth of the lymphatics has been tested by a large number of injections in every stage from the time tlie lymphatics first appear up to the time of birth. Every injection made into the ducts of the skin of the anterior part of the body will run to the lymph sac or the gland derived from it, if pushed far enough. The different systems of ducts of the neck can be brought out by injecting in four different places. When the needle is entered over the shoulder the injection mass invariably runs to the apex of the 28
Fio. 4. Diagrara of the anterior lymph heart in an embryo \ng, 3.6 cm. long. X 10. A, apex of the heart ; h, base of the heart and level of Fig. 5; ijv, internal jugular vein.
362
Dt>velo])iiu'iit of tli(> TAiiii)liatic Xoiles in tlie Pig
lymph sac; occasionally it enters tlie surface duets that anastomose with the long plexus. When the needle is introduced into the layer of the lymphatics between tlie eye and ear, or over the lower jaw and front of the neck, or into the pads of tlie fore feet, the injection mass runs into
Fig. 5. Transverse section through the neck of an embryo pig, 3.6 cm. long. X about 11. The shape of the entire heart of which this figure shows a section is given in Fig. 4, in which the line b is the level of Fig. 5. Ca, carotid artery; ejv, external jugular vein; ijv. internal jugular vein; Z, larynx; Ih, lymph heart; Ip, lymph plexus along the external jugular vein; nv, vagus nerve; oe, oesophagus; scm, sterno-cleido-mastoid muscle; sn, sympathetic nerve.
the long- plexus and across the sterno-cleido-mastoid muscle to the apex of the lymph sac. This general relation is not only true in the stages already pictured, but in the later stages when the apex of the lymph heart is a lymph node and the long plexus has been replaced by a chain of lymph nodes.
Florence 1». Sal)in
563
As is seen in Fig. (!, the duets which connect the lynipli sac and the loiiii' plexus, join the ])lexus half way between the ear and the fore leg. Once or twice, out of many injections in which the needle w^as introduced between the eye and I'ar. tlie injection mass lias reached the veins in two ways: one the usual course through the lymph heart, and secondly, through ducts that follow the course of the external jugular vein to its junction with the internal jugular, showing that the ducts along the two veins anastomose.
Fig. 6. Lymphatics in the neck of an embryo pig, 6 cm. long, showing the modified lymph heart in the depth and the plexus of lymphatics along the external jugular vein, x about 3. B. lymph node developing in the base of the lymph heart; e, extravasation at the point of injection; Ip, long plexus of lymphatics along the course of the external jugular vein; pin, primary lymph node developing in the apex of the lymph heart.
Fig. 7 is from a pig 11 cm. long and shows an injection of the lymphatics made from two points : one between the eye and the ear, and the other into the foot pad. The injection mass, both from the ducts of the face and from the fore leg, has entered the long plexus and then
364
Development of the Lympliatic Nodes in the Pig
passed through ducts that lie over the sterno-chleido-mastoid muscle into the node representing the l3anph heart (pin). At this stage there are two lymph nodes at the angle of the jaw, nf, one deeper, receiving the ducts around the eye and cheek, the other more superficial, receiving the ducts just in front of the ear. The rest of the long plexus is also being modified into lymph nodes, one of which is in the middle of the plexus where the ducts join with the lymph sac, the other is at the posterior end of the plexus and drains the fore leg (nfl).
Fig. 7. Lymphatics in the neck of an embryo pig, 11 cm. long, x 1%. Lp, lymph plexus which lies parallel to the external jugular vein; nf, nodes developing in the long plexus draining the face; nfl, node developing in the long plexus and draining the fore leg; pin, primary lymph node between the trapezius and sterno-cleido-mastoid muscles.
Since the spread of the superficial lymphatic capillaries in the skin of the pig is practically complete when the embryo is 6.5 cm, long, it may be well to sum up the superficial lymphatic system at that stage. In the neck there is, in the depth, the lymph heart now considerably modified by the formation of lymph nodes. It has one large efferent duct along the internal jugular vein and one along the main superficial vein of the shoulder. Secondly, there is a plexus of ducts along the external jugular vein; this plexus connects freely with the lymph heart. Lymphatic nodes in the neck are to be found developing first from the lymph sac, secondly in the long plexus on the course of the external jug
Florence E. Sabin 365
ular vein, and thirdly in the depth along the internal jugular vein. In the surface the capillaries have grown from the apex of the l3-mph heart to the shoulder and back of the head and from the long plexus to the face, neck, thorax, and fore leg. The capillaries of all these sets of ducts anastomose freel}^ in the skin and there are no valves to check the spreading of an injection mass. The lymphatics of the axilla belong to the deep set which grow along the arteries rather than the veins.
The spreading of the lymphatics for the lower part of the body can be constructed from Fig. 5, Vol. Ill, p. 188. The position of the posterior lymph heart is just caudal to the kidney, and at this point a h'mpli node develops. The superficial lymphatics for the lower part of the body grow in two directions, one set following the vein to a point over the crest of the ileum, where a node is formed which drains the skin of the back and hip; the other set coming to the surface in the inguinal region where a long node is formed which drains the abdominal wall and the hind legs. These three nodes with the abundant chain of nodes along the aorta represent the distribution of the glands which drain the skin of the lower part of the body. In following the histogenesis of the lymph nodes all of these different nodes have been studied, but most of the figures presented are from different stages of one node, namely, the first one to develop in the body.
Histogenesis of the primary lymph node. — We turn now to the histogenesis of the lymph node, which will involve determining the structural unit, and tracing the two elements, the vascular element with the adenoid tissue, and the lymphatic element or sinus.
The first lymph node in the body develops from the apex of the lymph heart and will be referred to as the primary lymph node. This node will be traced in its development until its condition, is practically adult.
The first evidence of the formation of lymphatic nodes occurs when the embryo is 3 cm. long. At this stage the lymph heart, which has been a smooth walled sac, as shown in Figs. 3 and 5, lined with a single layer of endothelial cells, begins to show a slight modification at the apex in that bands of connective tissue begin to push into the lumen Avithout destroying the lining. The apex of the lymph sac is pictured in Fig. 8 from a pig 3.6 cm. long. The section is taken from the same series as Fig. 5, by which the transverse plane of the section can be noted. The figure shows the character of the surrounding tissue consisting of a syncytium of protoplasm with nuclei in the nodes. The wall of the sac consists of a single layer of endothelial cells, and in the left hand side there is no perceptible modification of the connective tissue. On the right
366
Dcvelo])nK'nt of the Lvinphalic Nodes in the Pig
side, however, bands of connective tissue project into the sac without destroying its endothelial lining at any point. The connective tissue in these bands and on tlie right border of the sac appears different from the surrounding tissue.
Studied with the oil immersion lens, the surrounding connective tissue appears as described by J\[all " to be a network of granular protoplasm in
Fig. 8. Primary lymph node from a transverse section of the neclv of an embryo pig, 3.6 cm. long, x about 60. The left side of the figure is the mesial side of the heart, the right side is toward the skin and shows the afferent ducts. The top of the figure is the position of the hilum of the node. Ld, lymph duct (afferent) ; lU. lymph heart; v, vein.
which are distinct anastomosing fibrils. The nuclei lie in the nodes of the network and each one has around it a drop of clearer protoplasm which he calls endoplasm, distinct from the rest or exoplasm. Xear the lymph sac, on the right hand side in the figure, are numerous blood capillaries and around each one are clumps of from 8 to 20 nuclei. These
"Mall: American .Journal of Anatomy, Vol. I, 1902.
Florence R. ^^al)in 367
nuclei lie definitely within tlie tiyncytiuni and belong to the connective tissue. They are only to be distinguished l)y the fact that they are in clumps and that some show karyokinetic figures while others are smaller and take the deep stain of a newly divided nucleus. In short, cell proliferation takes place around the capillaries.
Passing now to the bands or bridges of connective tissue, the first point to be noted is that there are numerous blood capillaries filled Avith red blood cells, many of them nucleated. The same sort of protoplasmic network is present as in the surrounding tissue, but the network is denser and the meshes finer. The increase seems to be in the granular protoplasm rather than in the fibrils. In this dense network of protoplasm are crowded many connective tissue nuclei ; the mature ones are oval in shape and take the stain faintly. Many of the nuclei are dividing, and there are numerous small, round, deeply staining, young nuclei. These round nuclei belong, however, to the connective tissue and there are no true wandering cells outside of the blood-vessels. Thus the modification of the tissue around the sac consists merely of an increase in the blood capillaries, and in the connective tissue protoplasm and nuclei. The cell increase does not take place independently of the blood capillaries. There is no muscle in the wall of the sac at any time. By the time the embryo is 3.6 cm. long a second node is Just beginning at the other end of the sac. This second node from the lymph sac develops in the same manner as the first, but slightly later.
We pass now to the primary lymph node when the embryo is 4.9 cm. long, as shown in Fig. 9. The section is taken in the same plane as Fig. 8, that is, it is from a set of transverse sections. The efferent ducts are on the right and the hilum at the top of the section. There are no striking changes between this and the preceding stage. The node as a whole has increased considerably in size. The lymph heart is about the same actual size as in Fig. 8, but the lymphatic plexus is greater. From Fig. 1 it can be seen that when the ducts first start out from the sac they grow directly to the skin, but in Fig. 9 there has been an anastomosis or plexus formation of the ducts on the border of the sac. This greatly extends the area of the node. On the left side of the sac there are a few blood capillaries with clumps of dividing nuclei around them. The bands of connective tissues shoAv the same abundance of blood capillaries and increase in the protoplasm and nuclei. Young and dividing nuclei are abundant, Init no true wandering cells are present.
A more important stage is met with when the embryo is 7 cm. long. From this stage on, the development of the primary lymph node is shown
368
Develo])nu'nt of the Lviiiplialie Xodcs in the Pig
in a series of five diagrams. Each diagrain is made from a single section traced with the aid of the camera lucida. The blood-vessels are put in freehand from the study of the complete set of serial sections from which each diagram was made. All the figures are of the same magnification.
Fig. 9. Primary lymph node from a transverse section of the neclv of an .embryo pig 4.9 cm. long, x about 44. The section is placed similar to Fig. 8. Ld, afferent lymph duct; Ih. lymph heart; v, vein.
about 33 diameters. The lymphatic vessels are shown in solid black as if injected, while the connective tissue of the hanph cords and follicles is dotted. In the later stages the increased number of the dots represents the increase in lymphocytes and the lines show the beginning capsule and trabecule.
Florence E. Sabin
369
In the first diagram, Fig. 10, tlie step in advance beyond the stage of Fig. 9 is in the proliferation of the lymphatic capillaries. The sac has been completely cut up into ducts. The entire node consists of a plexus of lymphatics which differs in no way from the plexus in the skin pictured in my first paper. There are the same swollen bulbs, the same blind sprouts and slender channels. The connective tissue bridges are similar to those of the preceding stages. They contain many dividing cells but no true wandering cells. In the bridges is an abundant plexus of blood capillaries which are not shown in the diagram. This diagram might also represent any lymph node which develops in a plexus.
To sum up, the figure marks the culmination of the first stage of the development of the lymphatic nodes in early embryos, namely, the stage in which the node consists of a plexus of lymphatic capillaries separated by bauds of connective tissue which is denser than the surrounding tissue. This stage is shown in Kling's ' models. Fig. 1. The connective tissue is embryonic in type, consisting of a net work of granular protoplasm with a few fibrils and with many nuclei. The bands or bridges have blood capillaries and the increase in connective tissue does not take place independently of them. There are no true wandering cells outside of the blood capillaries. It is the stage of lymphatic ducts and pure connective tissue bridges. All of the nodes of the early embryos, the primary nodes in the sense of Gulland pass through this stage. That is to say, the nodes which develop in the long plexus in the neck from which ducts radiate to the face, neck, fore legs and thorax (Fig. 6) ; or the node which comes in the inguinal region at the point where tlie ducts radiate over the abdominal wall and hind legs; or in the node over the crest of the ileum where they radiate over the back (see Fig. 5, Vol. Ill, p. 188). All of these nodes come in places, where plexuses are formed because ducts radiate over a wide area, which is shown well in the figure just quoted. They are primary nodes in the sense of Gulland because they develop early and drain large capillary areas. It will be shown subsequently that lymphatic
Fio. 10. Diagram of the primary lymph node in an embryo pig- 7 cm. lonjr. X about 53. The lymphatics are in solid black and the connective tissue bridges are dotted.
Ibid
Development of the Lvniphatic Xodes in the Pig
nodes which develop later in the life of the embryo, after lymphocytes occur, hurry through the prinuiry process, and show a considerable modification of it.
Up to this time the node has had none of the structures characteristic of the adult node; there are no lymph cords, nor germ centers, no lymphocytes, and no sinuses.
The next stage, pictured in Fig. 11, shows the beginning of some of these structures. The diagram is made from a section of the primary lymph node in a pig 8 cm. long. In the center of the node the blood capillaries have proliferated, giving a tuft of capillaries surrounded by
Fig. 11. Diagram of the primary lymph node in an embryo pig, 8 cm. long. X about 33. This represents the primordial follicle. The hilum is marked by the artery. A. artery; aid. afferent lymph duct; eld, efferent lymph ducts; f. follicle.
connective tissue. The artery is shown leading up to the node but reduced to capillaries on entering it. The vein is not shown in the diagram, but the artery and vein lie parallel, up to the point where the node or follicle is entered, where they separate. This is an important ancT characteristic point in the relation of the blood-vessels. At this stage there are only capillaries within the node.
Here for the first time we can speak of the lymph follicle, wliich is the vascular unit and consists of the structures that go with a single artery. At this stage the entire node is one follicle. Here also for the first time two elements are differentiated, a lymphoid element connected with the artery and a lymphatic element made of lymph ducts.
Florence 11. Sabin 371
The point of entry of the artery determines the hihim of the node. The position of tlie hiiuni is determined from the lieginning of the formation of the node hy the lines of growth. Hh^od-vessels and lymphatics grow from the center of the body to the periphery, so that the proximal surface of the gland has from the start the entering blood-vessels and the efferent lymphatic ducts, while the peripheral surface of the node is the place from which the efferent lymphatic ducts radiate to the area they are to drain. In the central core of connective tissue the lymphatic capillaries are reduced in number and size; they are never quite absent but do not appear except in well-injected specimens. The presence of these ducts within the connective tissue core may have some liearing on the pathology of lymph nodes. The disappearance of the lymph capillaries in the center of the node involves the retrogression and absorption which is characteristic of developing tissues. Throughout the evolution of the lymph node there is continnal building up and tearing down. This will be evident in later stages where there is a continual change in the proportion of the lymphoid structures or cords and the lymphatic structures or sinuses.
Beside being the stage which marks the beginning of the adult structures of the node, that is to say, of the follicle, this stage also shows fundamental changes in cell differentiation. It marks the beginning of the wandering cell in lymph nodes. Up to this time the connective tissue part of the node has consisted of a network of granular protoplasm with many nuclei, young, dividing, and old. At this time three types of wandering cells appear, the lymphocyte, the polymorphonuclear form, and the eosinophile.
Lymphocytes are present in the thymus at a much earlier stage, they are abundant there in the sections from the enil)ryo 3.6 cm. long. In the sections of the lymph node at 8 cm., there are a few lymphocytes in the connective tissue core of the node, and in little clumps in the connective tissue just without the node. These little clumps of cells are found near the capillaries. The differences between the connective tissue cell and the lymphocyte are as follows: The nucleus of the former is large, faintly staining, and oval in shape, and the protoplasm belongs definitely to the network, while the latter has a small, round, deeply staining nucleus, with a more distinct nuclear membrane. The nuclear network and the chromatin granules are coarser, and there are one or more nucleoli. Moreover, the protoplasm makes a narrow but definite rim around the nucleus. Between the connective tissue cell, especially the _young forms, and the lymphocyte one can see every possible transition.
3T2 Development of the Lviiipliatic Xodes in the Pig
Often the connective tissue nuclei appear as if being extended from the protoplasmic network of exoplasm, the irregular endoplasm still clinging to the nucleus.
This form of observation cannot be considered as proof of the origin of the lymphocyte from connective tissue — it is obvious that the position of a wandering cell cannot give evidence of its origin. With the same t3'pe of tissue to examine, Gulland, noting the occurrence of the lymphocytes in clumps around the capillaries, concluded that they were filtered from the blood stream. The evidence does not suffice to prove either that the lymphocyte develops from the connective tissue in the lymph node, nor that it reaches the node through the blood stream. "We must await some new method of attacking this problem. One point is, however, definite in my specimens — that cell division in the connective tissue takes place in little clumps around the blood capillaries, and, as will be shown later, the division of the lymphocytes takes place also around tufts of capillaries.
Besides the lymphocytes there are a few polymorphonuclear cells at this stage, perhaps not more than twenty or thirty in each section. They are quite typical, having irregular nuclei and finely granular protoplasm. They occur within the follicle. Eosinophiles appear also for the first time. Within the follicle there are numerous red blood cells outside of the capillaries, showing signs of degeneration, that is, a vacuolization and a breaking up of the protoplasm into granules. These granules are all of the same size and cannot be distinguished from the granules of the eosinophilic cell. This is the same evidence that has led Weidenreich to the conclusion that the eosinophilic granule comes from the red blood cell. It is suggestive, but not conclusive.
To sum up the stage represented by Fig. 11, it marks the beginning of the dift'erentiation of the node into its two elements, lymphoid and lymphatic. It shows the beginning of the follicle and of the wandering cell. There is a marked proliferation of the blood capillaries and a consequent increase in the connective tissue in the center of the node. This involves a retrogression or destruction of some of the lymph ducts. At the same time wandering cells appear, lymphocytes in greatest numbers and also polymorphonuclear leucocytes and eosinophiles. There is also evidence of degeneration of the red blood cells.
The next stage is shown in Fig. 12. It was made from the primary lymph node of a pig 13 cm. long. The first point to be noted is the development of the artery. Without the limits of the node, the artery has divided into two branches. These two branches enter the node and
Florence E. Sabin 373
divide into five main branches and two mnch smaller ones. Consequently there are five definite primordial follicles, and two small ones. Both of the small ones and two of the large ones show in the section. At this stage there is no definite capsule, the limits of the node being determined by the lympliatic vessels. The nodes increase in size by invading the surrounding tissue, for example, the artery which here branches without the node is subsequently included in the gland. This stage marks several important changes. Tlie first has already been noted as being the division of the artery and the corresponding multiplication of the fol
FiG. 12. Diagram of the primary lymph node in an embryo pig, 13 cm. long. X about 33. The section shows two large follicles and two small ones. A, artery; aid, afferent lymph ducts; bf, beginning follicle; ehl, efferent lymph duct; f, follicle; gc, germ center.
licles. The vein, which is not shown in the diagram, runs parallel to each branch of the artery up to the point where the artery enters the follicle. On entering the follicle artery and vein separate and both break up into plexuses. At this stage the artery without the follicle can be distinguished by a thickening of the connective tissue around, there being no media, and by its smaller caliber. The vein has only a lining of endothelium and there is as yet no thickening of the adventitia. Within the follicle, the vessels are all capillaries, but the plexus which connects directly with the artery is made of smaller vessels than the plexus which connects with the vein.
374 l)(>V(.'Ki)iiiK'nt of the Lvnipliatie Xodos in the Pig
Tho soeoiul point in advance is the formation of the germinal center. AVithin the follicle, as will be seen in the diagram, there are small clnmps of colls, definitely lymphocytes, heaped aronnd a capillary tuft. In the entire node at this stage there are eight of these germinal centers. The lymphocytes are closely packed in them, and there are more lymphocytes near these centers than elsewhere in the node. In regard to the wandering cells, the follicles contain in general four types : First, the lymphocytes which are found in the germinal centers almost to the exclusion of any other free cell. A few of them are to he seen near the germ centers. Second, polymorphonuclear forms, which are scattered throughout the follicle except in the germ centers. Third, eosinophilic cells. Fourth, mononuclear forms which have larger nuclei and more protoplasm than the lymphocytes. All of these cells are found in the follicle. Eed blood cells are also present, many of them being free in the connective tissue meshes and showing a breaking up of the protoplasm into granules. This appearance of the red blood cell is seldom seen in the corpuscles within the capillaries. The bridges of connective tissue between the lymph ducts have fewer wandering cells than the follicle.
Beside the two changes already noted, namely, the division of the artery and consequent multiplication of follicles, and secondly, the differentiation of the follicle into germ center and lymph cord, there is a third important change, namely, the beginning of the formation of lymphatic sinuses out of the lymphatic ducts. It will be noted in the diagram that around the border of the follicle the lymph ducts are arranged in rows closely packed together and that the connective tissue bridges between them are slender. This is still more definite in the next diagrams given in Figs. 13 and l-l. In section, this point is to be seen in Fig. 15, where the surface of the node adjacent to the capsule is made of a plexus of lymph ducts, while in the depth of the node the ducts are closely packed together in certain areas making sinuses. The section shows all gradations in the width of the connective tissue bridges, some being just wide enough to contain a single nucleus while others are broad bands.
Kling was, I think, the first to note this method of the formation of the sinus, though he clouded the clearness of his picture by saying that subsequently the bridging of the sinus is made by the stretching of endothelial cells across the lumen of the ducts, so that there are bridges made of endothelium alone. This appearance is undoubtedly found in sections just as in sections of the lung the epithelial lining of an air sac sometimes shows as a membrane.
By following the evolution of the sinus it is possible to understand clearly the relation of the reticulum of the adult sinus to the endotlielial
Florence R. Sabin 375
cells. The reticulum fibers develop subsequently in the connective tissue bridges (not. as Kling says, from the endothelium). Tlie lymph ducts from which the sinus is made have a complete endotliolial lining. Moreover, the increase in the ducts which form the sinus takes place by the same process of the budding of endothelial cells which characterizes the development of lymphatics or blood-vessels elsewhere. Thus the spaces of the sinus are lined throughout by endothelium. The sinus can be pictured in three dimensions by imagining the follicle surrounded by a plexus of ducts so dense that the bridges between them are reduced to the thickness of a single network of fibers. Such a structure in cross section would give the appearance of fibers with endothelial cells around them cutting the lumen of the sinus. As a matter of fact the fibers are between the endothelial cells and without the lymph channels. They connect with the rest of the connective tissue framework of the node as is readily seen in Fig. 12.
The next stage is from a section of the primary lymph node of an embryo 15 cm. long (Fig. 13). There is now a great development of the artery. The wall of the artery has developed considerably and shows one row of smooth muscle cells beside the adventitia. The vein which lies beside it has only an endothelium and a thickened connective tissue sheath. The artery divides into three main branches on the edge of the node, and within the node each branch subdivides several times. As in the early stage, the artery and vein run parallel until the follicle is entered and there they separate. The amount of lymphoid tissue has increased parallel with the development of the artery. The sinuses are growing down into the node between the arteries, thereby surrounding and limiting the lymphoid masses around the blood-vessels. By this process the lymph cord along the blood-vessel becomes defined, as will be clear in the next diagram.
The especial advance in this stage lies in the connective tissue, for here the reticulum fibers within the node first begin. Up to this stage the connective tissue of the node has been a protoplasmic network with delicate anastomosing fibrils which, however, do not stain sharply by Mallory's method. Xow for the first time there are a few fibrils which stand out clearly in the Mallory stain. They occur in the germ centers where they are laid down in concentric circles. With the oil immersion lens it can be seen that the fibers of the germ centers make a definite mosaic of polygonal spaces in concentric rows. All of these polygonal spaces thus outlined are filled with cells. This appearance of the mosaic can be seen in thin sections of the adult node and can be brought out by silver nitrate.
376 Development of the Lymphatic Nodes in the Pig
The diagram shows the first beginning of the trabeculas in the connective tissue that pushes down between the peripheral sinuses as these surround the follicles (see dt on the figure). Neither the capsule nor the trabecuhiB have fibers different from the surrounding connective tissue at this stage.
There are certain interesting points in regard to the cells of the node at this stage. In the germ centers there is a marked division of the
Fig. 13. Diagram ot the primary lymph node in an embryo pig, 15 cm.
long. X about 33. The node shows several follicles. A, artery; aid, afferent
lymph ducts; dt, developing trabecula; gc, germ center; ps, peripheral sinus.
lymphocytes. In any one section each center contains from two to fifteen or more dividing lymphocytes. They are easily distinguished from the dividing connective tissue nuclei, which are always larger and have much more protoplasm. There are many eosinophiles in the cords, but at this stage none are to be found in the germ centers. There are numerous degenerating red blood cells.
The next diagram (Fig. 14) is from the primary lymph node in a pig 23 cm. long. Only a portion of the section was drawn, in order to
Florence 11. Sabin
3?7
fceep the diagram at the same magnification as the others. An outline of the entire section is shown in the margin. It gives the artery and a few eiferent ducts at the hihim and also a large trabecula (t), carrying alferent ducts. This trabecula connects with the cortex in another section of the sx^ries. The left hand part of the section shows a consid
CCS
Fig. 14. Diagram of the primary lymph node in an embryo pig, 23 cm. long. X about 33. The diagram was made from a segment of a section, the outline of the entire section being given in the margin. A. artery; c. capsule; cs, central sinus; dts. developing trabeculag of the sinuses; ed. efferent duct; gc, germ center; /c, lymph cord; 7p, lymph plexus; ps. peripheral sinus; t, trabecula with afferent ducts.
erable advance over the preceding stage; it represents practically adult conditions where the entire node has been transformed into lymph cords and sinuses. This change has come aljout in the following manner: The lymph duct plexus or sinus, which was only on the edge of the preceding section, making the peripheral sinus, has now grown into the 29
378 Devolopiiiciit of tlu' Ijyiii|iltatie Xodos in tlic Pig
depth botwoen the arteries, thert'hy exteiuliiii;- the sinuses and definitely limiting the lymph cords. Indeed, the true lymph cord of the adult condition now appears for the first time. The diagram shows well the nature of the lymph sinuses consisting of rows of closely packed lymph ducts. The bridges between them are still protoplasmic and slightly wider tlian they appear in the adult nodes.
The diagram shows the rel-ition of the trabecula? to the capsule and the sinuses. Here for the firsi time there is a definite capsule and it is interesting to note that it is not complete. It extends along the margin of the peripheral sinus but ends abruptly on the right hand side of the section, where the node consists of a plexus of lymph ducts. It will be noticed that there is a definite indentation in the margin of the node where the capsule ceases. At this place the node can increase in size by invading the surrounding tissue.
The structure of the capsule itself is best studied in good Mallory specimens with the oil immersion lens. For this study it is necessary to note the condition of the surrounding connective tissue. This has been described by Professor "Mall." There is in the first place in tlie surrounding tissue a delicate network of fine but definite anastomosing fibrils. The nuclei of the network are in the nodes, and most of them form part of the characteristic spindle cells. This is the prefibrous tissue of Mall; the fine fiber network is still slightly granular, representing the protoplasmic syncytium of the earlier stages. Most of the definite protoplasm is around the nuclei. Beside this fine fiber network there are large bundles of definite fibers. The fibers of these bundles are several times the width of the fibers of the network, and the bundles themselves are often eight or ten times the diameter of a red blood cell in width. Many of these bundles have several spindle cells clinging to them. The large bundles are found near the border of some gland or muscle, while in the less differentiated areas every transition between the fine network and the coarse bundles can be made out. As Mall has shown, these are the white fiber bundles developing from the prefibrous tissue. The fibers of the bundles are close together and are straight. The capsule of the lympli node is different both from tlie fine network and from the white fibrous bundles. It consists of a dense network of anastomosing fibers. These fibers are larger and sharper than the fine fiber network, but they are much finer than the fiber bundles. They are wavy and closely packed. In other words, they differ from the fine fiber network by being larger, sharper, and more closely packed, and
Ibid.
Florence E. Sabin 379
from the fiber bundles by running as separate, wavy fibers, having in general the same direction but forming abundant anastomoses. These are obviously the beginning reticulum fibers.
There is one small, fat organ within the capsule. The trabeculse are formed, as can be seen in the figure, by the folding in of the capsule, thereby bringing the trabecule in the center of the sinuses (dts). This shows especially well in the border of the large central trabecula (t) of the figure and explains why the trabecule of the adult node are bordered by sinuses. The traljecula.^ often carry blood-vessels from the capsule. The tissue around the Idood-vessel at the hilum thickens to form trabecular; these trabecular follow the veins farther than the arteries for the arteries soon enter the lymph cords. The trabecular around the bloodvessels are less developed at this stage than the capsule.
The connective tissue framework within the node itself is a definite protoplasmic network with a few fine fibrils which do not stain sharply in tlie Mallory stain except possibly in the germ centers. The bridges in the sinuses are all protoplasmic at this stage. In other words, the connective tissue framework of the node is less advanced than the surrounding tissue and the reticulum fiber is a later development.
The diagram shows the relation of the lymph cords and the germ centers. As has been said, the cords are first definitely outlined and restricted to the borders of the artery by the development of the lymph sinuses. Some of the cords arc narrow and have the single central artery, but the majority have an abundant plexus of blood-vessels. The arter}' and vein never run side by side in the lymph cord, and the veins leave the cords to enter the trabeculge that grow in from the hilus. At this stage of development only the large veins are in the trabecule. The germ centers are around the capillary tufts where the lymphocytes actively divide. The lymphocytes then wander down the borders of the artery, filling up the lymph cords. In the adult node, as is well known, the germ centers may present two diiferent appearances. In the one case, the center is uniformly filled with lymphocytes which are actively dividing: in the other case the lymphocytes are crowded to the edge of the germ center, giving the appearance of a dark rim in sections stained in hfematoxylin. In the einl<ryo wliere cell division is active, the germ centers are always uniformly crowded witli Ivmphocytes.
The right-hand part of the section is far less developed. It consists of a plexus of lymph ducts with connective tissue bridges which contain a network of blood capillaries ; it is essentially in the stage of Fig. 7, llioiigli the lymphatic plexus is more abundant. IMost of the nodes in
380 Dovelopnieiit of the Lymphatic Nodes in the Pig
the pig at this stage have the center made of definite cords and sinuses and the entire periphery made of a plexus of lymph ducts; and this is the condition of the primary lymph node in a pig 2 weeks old. That is to say, there are three kinds of tissue in the nodes : first, lymph cords and germ centers ; second, lymph sinuses ; and thirdly, plexuses of lymph ducts not yet transformed into sinuses. It is clear that the lymph plexus is a stage in the development of tlie lymph sinus, and hence is a less highly developed structure.
These points are clearly shown in Fig. 15, which is taken from the inguinal node in a pig 2-1.5 cm. long. A portion of the capsule is shown which is not as yet a limiting membrane. The outer part of the node consists of a plexus of h'mph ducts with connective tissue bridges. The nuclei in these bridges are large and oval. The inner portion of the node, away from the capsule, consists of lymph cords and sinuses. Within the cords the predominating cell is the lymphocyte, with which the germ centers are closely packed. The sinuses are groups of lyiuph ducts and transitions between the lymph plexus of the edge of the node and of the developed sinus are to be seen.
In the pig the lymph plexus persists up to adult life. In specimens where the lymph ducts are all collapsed, these areas look like masses of connective tissue, hence Delamere^ pictures them and calls them homogeneous areas. Eanvier " found the same tissue in the ]uesenteric nodes of the pig, but since his specimens had the lympli ducts distended he called the areas cavernous or erectile tissue. As has been said, in studying large numbers of lymph nodes in fresh specimens one often finds the lymph ducts or sinuses so distended Avith fluid that all the spaces are rounded. The presence of this lymph plexus not developed into a sinus in the nodes in the pig is, I believe, an important point not only in the study of development but in the understanding of the structure of allied organs. In all of the hsemolymph nodes I have seen, there have been three types of tissue, the lymphoid areas, true sinuses, and zones filled with blood but not definitely sinuses. These zones appear like veins not crowded enough to be sinuses.
We have thus followed the development of the primary lymph node which comes from the lymph sac. The stages are, in brief : first, a preliminary stage in which the entire node consists of a plexus of lymphatic capillaries with connective tissue bridges containing blood
" Poirer, Cuneo, and Delamere: The Lymphatics, p. 100, translated from Poirier's Anatomie.
^"Ranvier: C. R. Acad. Sciences, 1S95, p. 800, or C. R. Soc. Biol., 1895, p. 774.
Floronce II. Sabin
381
« o- -i. J ! A ^t:'Mm3C
'■A
IrotiecuLa
.^mp
cord
Gerra centre — >rr=:
BLood.
vesseLs
Lumphatii^ plexus
CocpsuLe
■<iv^ ""~ ai'^-T'
Fig. 15. Portion of the inguinal lymph node in an embryo pig, 24.5 cm.
long. ' X about 200. Drawn with a camera lucida. The drawing shows the
transition between the lymphatic plexus hear the capsule and the sinuses farther within the node.
383 Devi'Idpiiu'iit of the Lyiiiphalic- Xoilo:^ in the Pig
capillaries; then a stii<ie in which the development of the l)h)oil-vessels determines the pi-imordial follicle. Followinii; the evolution of the artery the adenoid tissue is determined while the lymphatic part of the node, or the sinuses, develops from the proliferation of the lymph ducts, in the pig the adult node still contains some of the lymph plexus which in higher animals is completely transformed into the sinuses.
Derclopnieni of nodes in the [iriiunrij plexuses. — The other early lymph nodes which drain the skin develop in certain definite areas. If we limit the group to those which receive ducts directly from the skin without passing through other nodes, these glands develop in the long plexus around the external jugular vein in the neck and in the plexus of the inguinal region, and over the crest of the ileum. The development of the nodes in all of these areas has been studied. These nodes all begin in a plexus of lymph ducts rather than in a lymph sac ; the connective tissue bridges at first show no thickening but soon the nuclei become more crowded and the nodes pass through the various stages shown by the primary lymph node. The node over the crest of the ileum is the simplest, for like the primary lymph node it develops as a single node. The long plexus has the most complicated development and it drains a varied area. In the series at 7 cm. long the entire plexus shows a thickening of the connective tissue bridges. Suhsequently, as shown in Fig. 7, the plexus represents a chain of nodes. In this figure four macroscopic nodes are shown, two at the angle of the jaw, one about the center of the plexus, and the fourth at the lower end of the plexus. Of these nodes the one nearest the angle of the jaw receives ducts directly from the skin of the face around the eye ; the other node receives ducts both from the skin over the head and from the first node. The node in the middle of the plexus receives ducts from man}^ sources, in fact from all of the other glands in the chain and from the front of the neck as well, while the fourth node receives ducts from the fore leg. Thus it will be seen that some of the nodes are secondary or intermediate in the sense of receiving ducts from other nodes. Some nodes, for example those along the internal carotid artery, receive only ducts that have passed through other nodes, that is, they develop along the etferent ducts of a node, while some receive ducts both directly from the skin and from other nodes. In short, a gland may be secondary for some ducts and primary for others.
The histogenesis of these various nodes follows the same general lines as the primary lym])h nodes, beginning witli the stage represented in Fig. 10, but there is the widest possible variation in the relative pro
Floronee i\. .Sabin
383
portions of the lyniphoid tissue and the lymphatic tissue. Sometimes the lymphoid tissue, that is, tlie connective tissue ])ortion with lymphocytes arouiul the artery, nearly fills the node while in other cases the lymphatic ducts predominate.
Development of the folJlde liKtepenileiitli/ of the h/iitplt duels. — One im})ortant fuiuhimental jioint comes out in the study of these
K.10<v.
Fig. 16. Group of microscopic lymph follicles in the neighborhood of the inguinal lymph node in an embryo pig, 24.5 cm. long, x about 72. The condition of the main inguinal node at this stage, is shown in Fig. 14. A. follicles consisting of lymphocytes around a tuft of blood capillaries; &. follicles with a single peripheral sinus; c, follicles which are made mainly of a plexus of lymph ducts; Id, large lymph duct; Ip, lymph plexus in the border of a large lymph node.
various mxlc^. After a certain sta.iic in development, the larg-e nodes, especially those that develop in the Ion-;- ple.xus and in the inguinal region, show many microscopic nodes in their neighborhood. These microscopic nodes are abundant in emliryos from 2"? cm. long on. Fig. 16 is a section in the ])order of the inguinal node in a pig 24..") cm. long,
384 Development of tlie Lympliatic ^NTodes in the Pig
showing seven microscopic nodes. These different small glands represent all stages in development.
In the figure there is an ahundant plexus of lymphatic ducts and around this plexus is a group of small follicles. Two of these nodes, marked a, consist of a collection of lymphocytes around a tuft of blood capillaries. Studied through serial sections, these small follicles (a) have no lymphatics whatever. Two of the small nodes, marked h. have a single peripheral sinus around the follicle while others, marked r, have an abundant plexus of lymph ducts not transformed into sinuses. The node in the lower edge of the section is shown only in part. It is the margin of a larger node and shows the peripheral zone of lymph ducts. This entire mass of follicles will be subsequently fused with the large inguinal node, which is one method of increasing the size of the nodes. The inguinal node at birth contains fewer of the smaller follicles in the border than at earlier stages. The study of these microscopic nodes proves an important point, namely, that the lymphoid part of the node or the lymphocytes in the reticulum occurs primarily with the arteries and blood capillaries rather than with the lymphatics. This was suggested by the angiogenesis of the primary node, but is proved by the fact that small nodes are found around the capillaries before they are reached by the lymphatics. That is to say, the follicle is primarily and essentially associated with the artery. That the follicle occurs in the adult without lymphatics is shown in the Malpighian corpuscles of the spleen. In Fig. 17 is a small lymph node found in the lung of an adult pig. It lies in the edge of a lymph capillary but is without a true sinus forming an integral part of the node itself.
To return to Fig. 16, the section shows that nodes which develop at later stages after the lymphocytes occur in the glands, hurry through the long preliminary process of the first nodes; that is to say, they begin at once with a heaping up of lymphocytes around a blood-vessel.
Themolympli nodes. — The study of the development of these nodes is incomplete. It has not yet been extended to all the areas in which the h^molymph nodes occur, but confined to the neck region and along the course of the thoracic aorta. The liEemolymph node does not occur in the neck of the pig until the embryo is about 23 cm long, showing that it is a considerably later development than the lymphatic node. From the time the embryo is 23 cm. long there are one or two small nodes to be found near the node which forms in the center of the long plexus (see Fig. 7). In the specimen at 23 cm. long the hffimolymph node is in the simplest possible stage consisting of a single follicle with a
Florence R. Sabiii
385
peripheral sinus filled with blood. It looks exactl}^ like the follicles marked h in Fig. 16, except that the sinus is filled with blood. The next stage looks like the nodes marked c in the same figure, while a tliird stage shows an increase in the lymphoid tissue.
The hfemohmiph node thus parallels the stages in development of the other nodes, except that its sinuses from the beginning belong to the blood-vessels rather than to the lymph vessels. In the lymphatic nodes the sinuses are made of the modified veins called lymphatics, while in the hffiuiolymph node they are made of the veins themselves. The espe
Ar-terx|
Fig. 17. Lymph follicle without a peripheral sinus, found in the edge of a lymph duct in the lung of an adult pig. X 66.
cial point in the development of the nodes which is not yet clear is the relation of the veins which make the sinuses to the rest of the bloodvessels of the node.
In all of the specimens of the hasmolymph nodes as far as they have been studied, that is in pigs up to 3 weeks old, the venous or sinus portion of the node predominates over the lymphoid element. The nodes show both the true sinus and the plexus formation observed in lymphatic nodes, but the developed sinus is mucli more limited in amount. This is also true in all of the htemolymph nodes I have seen from the adult pig. 'They consist of three elements, the lymphoid masses surrounded by true sinuses, and a considerable amount of a venous
386 Development of the Lvmpliatic Nodes in the Pig
plexus not transformed into the sinus. Thus the hsvmolymph node is a later and less developed organ occurring along the l)loo(l-vessels.
The luvmolymph node found in the neck of the pig is from the l)eginning a distinct organ, different in type from the lymphatic node. In the adult pig these IiaMnolymj)li nodes in the neck are sometimes fused into the same capsule witli an ordinary lymph node, hut the two remain as distinct structures with trabecuhv between.
Summary and General Discussion.
Follicle.— From the study of the development of lymph nodes we find that there are in general three types of follicles. The simplest follicle consists of a collection of lymphocytes in a reticulum around an artery and its capillaries. This type occurs in the embryo and probably in the adult. The second type consists of the follicle of the first type surrounded by the lymphatic sinus. This type occurs either singly or in groups in the ordinary lymphatic gland. In the third type the lymphoid follicle is surrounded by a blood sinus or a less developed plexus of bloodvessels. This occurs in the hai-molymph node and spleen.
Lymphocytes. — In connection with the nature of the lymphoid tissue it has already been brought out that the lymphocyte occurs in a fine reticulum around the artery and its capillaries. For the ultimate origin of the lymphocyte we have as yet no proof, but the lymphocytes divide, as Flemming showed, in the germ centers. The germ centers are definite organs around capillary tufts or glomeruli. In the embryo the division of lymphocytes is so constant that the germ centers are always filled with them. The lymphocyte develops independently from the lymph ducts.
General structure and rjroirtli. — In regard to the general structure of the node, it has been shown to consist of two elements — a lymphoid or vascular and a sinus element, which is either venous or lymphatic. Through the study of the development of the nodes, it becomes clear that the sinus comes from a plexus of ducts or vessels by increasing the number of ducts and reducing the size of the connective tissue bridges. In the pig the plexus element of the node is not completely transformed into the sinus in the adult, so that the node has three structures, the lymphoid element, the plexus, and the sinus. There are wide variations in the proportions of these elements.
The question of growth and increase in size of the lymph node is an interesting one, closely liound up with the process of absorption in development. All of the diagrams show that the nodes in the early stages increase in size by the invasion of surrounding tissue by lymph ducts.
Florence K. Sahiii 387
This point is hrou.iilit out hv coni})aring Figs. 5 and G, from the primary node at 3.(j and 4.!) em. long. The sections are cut in the same plane and can be related by the sac. It a^II be seen that the increase in size of the second is due to the development of the lymph plexus. This invasion of ducts can take place as long as there is no definite capsule. The capsule is a late development, as shown in the last diagram, where it is still incomplete. After the capsule is formed the nodes increase in size by the fusion of many small nodes in the neighborhood. The capsules of the smaller nodes become the trabecule of the larger ones. The marked tendency of the fusion of nodes in the pig has been noted by other observers. In the pig not only do the ordinary lymph nodes fuse, but a haemolymph node may fuse with a ])ure lymph node and the two remain distinct but enclosed in a common capsule. The primary lymph node from the lymjih sac, and the node over the crest of the ileum show but few of the small nodes in the neighborhood and hence few evidences of fusion. On the other hand, the inguinal node which represents a group of nodes in higher forms, appears like a conglomerate of small nodes in the new-born pig.
The lymph nodes give inuch evidence of a repeated tearing down and relniilding in the process of growth. For example, in passing from the stage of the first to the second diagram, there must be a destruction of many lymph duets in the formation of the primordial follicle. It will be noted that this destruction is not complete in Fig. 8, for there are a few lymph duets scattered through the follicle. In following through the diagrams it will be noted that there is a constant change in the proportions of the lymphoid or vascular portion and the lymphatic portion of the node. The small nodes of Fig. 16 make this point clearer. The youngest ones have a predominance of the lymphoid portion, the very youngest ones having no lymph ducts at all. Others have merely a peripheral sinus, while others slightly larger are made almost entirely of a plexus of lymph ducts. As these nodes develop farther the lymphoid tissue will increase until the balance of lymphoid tissue, sinus, and lymph plexus characteristic of the adult node is reached. This point illustrates the extreme variation met with in the development of the lymphatic apparatus.
Sinus. — The lymph sinus develops out of the lymph ducts by a multiplication of the ducts along certain lines. The areas in which the lymph ducts multiply until the connective tissue bridges are reduced to the thickness of fibers, are determined by the blood-vessels. That is, the einuses grow in between the arteries thereby bounding the lymph cords.
388 Development of the Lymphatic Nodes in the Pig
The sinus develops by a proliferation of the cndotlicliura of the ducts, and so, as Kling pointed out, each space in the sinus has its complete ring of endothelium. The fact that the sinus is made of a great number of small lymph ducts packed closely together explains why one cannot get the silver picture of a membrane of endothelium far beyond the periphery of the node. None of the membranes are large enough. In the embryonic stages the connective tissue bridges are largely protoplasmic and show connective tissue nuclei. In the adult the bridges are a network of reticulum fibrils so that the endothelial cells appear on the fibers.
The study of the contents of the sinuses will prove, I think, an important point in the physiology of the lymph nodes. There is a marked difference between the embryonic nodes and the adult in this respect. In the embryonic nodes there are few free, wandering cells in the sinuses as compared with the adult. In the early stages there are almost no free cells in the ducts. After the lymphocytes appear, they occur occasionally in the ducts and sinuses, as well as a few large mononuclear forms. As a rule the sinuses are nearly empty of the free cells, so that the bridges stand out with great beauty and clearness. In the adult node, on the other hand, the content of the sinus in free cells is most varied, both in the number and in the kind of cells. Sometimes the sinuses are so packed with cells that the reticulum and endothelium are almost covered up. It often happens that the sinuses of one portion of a section are densely packed with cells, while in another portion they are almost empty. These free cells may be any type of white blood cell or may be large phagocytic cells. The sinuses may be filled with phagocytic cells that are crowded either with red blood corpuscles or, in the mesenteric nodes, with fat globules.
Reticulum. — The complete relation of the connective tissue framework or reticulum can only be clear after noting the nature of the sinus. The reticulum fibers first appear in the germ centers where they make a mosaic pattern around the capillary tuft. The trabeculse develop from the capsule in connection first with the sinuses and secondly with the blood-vessels, especially the veins. The reticulum fibers are laid do^vm in a very close protoplasmic syncytium, and this syncytium remains protoplasmic long after the surrounding connective tissue has become predominately fibrillar. The reticulum fibers do not show until the embryo is 15 or 16 cm. long. They appear first in the germ centers and in the capsule. In an embryo 23 cm. long they are limited to the capsule and a few trabeculse, while up to the time of birth the connective tissue framework is still largely protoplasmic.
Florence K. Sabin 389
The reticulum framework in the adult makes a complete anastomosis throughout the node. The framework can be readily traced in the last diagram. Starting from the capsule, fibers enter the trabeculae, pass between the ducts of the sinus and enter the lymph cord. The large trabeculae carry veins. In a specimen of reticulum from which the cells have been digested out, the entire node can be reconstructed for the sinuses occur in the looser reticulum that borders the trabeculae while the cords and follicles are between trabeculae and show a much finer and denser network than the sinuses. The germ centers often appear as holes, since the fibers are delicate there.
Lymph capillaries. — The subject of open or closed lymphatics, within the lymph node as elsewhere, has given rise to most definite but opposite opinions. The study of development touches but one aspect of the question, unless it is combined with many injection experiments. The lymphatics develop as blind sacs from the veins and have a complete endothelial lining. The sinuses result from a multiplication of the lymph ducts and the only difference between the sinus and the preliminary lymph plexus is in the width of the connective tissue bridges between the ducts. In the sinus these bridges are reduced to the thickness of the reticulum fibers of the adult. Thus from the purely embryological argument the spaces of the sinuses have a complete endothelial lining. Numerous injections of lymph nodes in every stage have been made with Prussian blue and with India ink. The ink always runs farther than the Prussian blue. In injecting the nodes through the afferent ducts it is always easy to avoid undue pressure within the node, for the lymphatic area of the node is so much greater than the caliber of the ducts leading to it. It is possible in all stages up to two weeks after birth to obtain injections without extravasations. But many injections do show extravasations and these occur in the walls of the sinus rather than the less developed plexus of ducts which always forms a part of the node. This shows that the wall of the sinus is weaker than the walls of the plexus.
To conclude, the present study shows the close relation between the lymphatic system and the vascular system. In the formation of lymph nodes, haemolymph nodes, and spleen, there is one fixed element in common, namely, the lymphoid tissue associated with the artery; the fluctuating element or the sinus belongs either to the venous system or to modified veins called lymphatics. The sinus may be absent, or venous or lymphatic.
On The Angle Of The Elbow
By
Franklin P. Mall.
From the Anatomical Laboratory of the Johns Hopkins University.
With 1 Figure and 8 Tables.
Artists consider a woman's arm beautiful when, in its extended position it is straight, or nearly so, and sufficiently plump to give it delicate curved lines. With the elbow flexed the upper arm is considered the more beautiful the nearer its section approaches a circle. The same is claimed for the forearm near the elbow. As the section approaches the wrist the circle becomes an ellipse, and the farther it is from the elbow the more marked is its eccentricity. With the forearm flexed and semiprone the long axis of the ellipse is directed diagonally downward and outward. It is self-evident that artists do not make either cylindrical or conical arms; they prefer as a model an arm whose section is nearly circular. The foreann is always a little flat, more so in supination than in pronation. In antique statues the upper arm is found to be more nearly circular, while in those of the renaissance a lateral flattening is shown. It appears then that the ideal arm of artists changes from time to time, possibly because the models before them changed correspondingly. At any rate the shape of the upper arm of the renaissance approaches the modem anatomical arm more than does that of antiquity.
The form of the ideal woman's arm is caused in great part by the layer of subcutaneous fat drawn over the structure below. In the ideal man's arm the structures below, especially the muscles, protrude and form marked lines indicating strength. And it is considered beautiful by many to show some of these lines in a delicate way in" woman's arm. A slight outline of the deltoid, biceps and triceps does not make the arm appear masculine provided it is built upon a delicate skeleton.
The beautiful arm, then, is one that is plump, round, tapering and relatively straight. Differences are, of course, to be expected, due to race, sex and age. The amount of fat upon the arm differs much between the ages of 15, 25 and 45. The same seems to be true regarding the angle of the elbow. The arms of young girls are said to be straighter and
American Journal of Anatomy. — Vol. IV. 31
392 On the Anglo of the Elbow
the motion of the elbow seems to be greater than are those of young women. At any rate, from an artistic standpoint, a slight amount of hyperextension is permitted in a child's arm, but it makes a bad impression when it is present in the arm of a muscular man. It is evident that the standard of the beautiful must change for different periods of life, and the question is whether the beautiful and anatomical normal correspond. It was mentioned above that the arms of antique statues were unlike in form those of the renaissance, the latter being more realistic.
The Greeks constructed the canon of the human body with its length eight times the length of the head, which was taken as the modulus. This gave a rather short body, too much so, for Michael Angelo found it necessary to add one-third of a modulus, making the body 8^ heads long. This third of a modulus was added to the legs above, which were also extended one-sixth of a modulus below. Thus Michael Angelo's canon is half a head longer than the Greek canon, all of the difference being added to the legs. This may account for the plump arms of the Greeks and the thinner arms of the renaissance. Since that time many systems of measurement have been invented, differing mostly in the modulus, and contributing little to the proportion of the body. It appears that the first scientific step was taken by Quetelet, who drew averages from the measurements of some 30 soldiers. So much variation was encountered, however, that his results proved to be of little value. Others made many measurements, as is shown by Sargent's admirable work on the average figure of American students of both sexes. The next step in advance was made by measuring from the principal joints to obtain the proportions of the trunk, and the most satisfactory system is that of Fritsch, whose modulus is the length of the spinal column. His canon, to a certain extent, outlines the human body, giving at a glance many ratios. When this is compared with numerous recent outlines it is remarkable how well they coincide. It may be added that the best recent outlines of the body were constructed by anatomists and that there is now a tendency for artists to accept a canon which is anatomically correct. Furthermore, this canon is much more like that of antiquity than like that of the renaissance, being half a head shorter than the Greek canon.
The difficulty is not to be solved by inventing a new modulus but by establishing its length. This in turn will establish the length of all other important measurements, bringing ultimately the artistic ideal and the anatomical normal together. Furthermore, measurements from the centers of the main joints are most desirable, for then exact measure
Franklin P. Mall 393
ments can be made in a statne, since a femur or a humerus measures the same in all positions. Fritsclfs canon fulfills this requirement. That the average measurement is the most beautiful is further proved by observing composite photographs of many average faces, few of which are considered beautiful, while together they are decidedly so. Nature has here been and must continue to remain our best standard.
To what extent artists may idealize variations is not for me to consider now. They must, however, remain within bounds, and when they emphasize a variation of one part their convention must make the rest of the body the anatomical normal in order to bring out well the difference. So if straight arms are the artistic ideal, the rest of the canon must correspond with the anatomical normal.
In a model an arm is not considered beautiful if it is too long, for this is said to be indicative of a lower race. Neither is hyperextension nor a lateral angle considered desirable. It is especially inartistic to have the two combined. Hyperextension of the elbow may be overlooked in children and in delicate girls, for it helps to indicate the flexibility of the body, which is a characteristic of youth.
It appears that those who write upon the angle of the elbow from the standpoint of the artist are not altogether familiar with its anatomy, for the straight arm is considered the more usual. According to Briicke, the lateral deflection of the forearm is more common in women than in men, while according to Stratz the opposite is the case.
The latter author makes the normal arm so straight that the wrist in turning rotates in a circle with the radius as its center, thus in pronation the lower end of the ulna moves lateral as much, or more, than the radius does medial (see Stratz's Fig. 67).
It has been known for a long time that the trochlea is not set at right angles to the shaft of the humerus but obliquely to it, making an acute angle directed outwards. It is this lateral angle which, according to Langer, causes the forearm to bend out when the arm is extended, and assuming that the articular surfaces of the ulna and radius are at right angles to the forearm the hand must fall upon the chest when the elbow is flexed. The amount of lateral deflection when the arm is extended equals the extent the hand moves in when tho arm is flexed. The observations of Langer are accepted by Briicke, but apparently he does not consider the normal arm beautiful, and suggests various methods by which it can be corrected in a picture or a statue by always presenting the arms either partly pronated, or partly flexed, or both.
The subject was carefully reworked by Braune and Kyrklund in their study of the elbow joint, and they show that not only is the axis of
394 Oil the Angle of the VAhow
the elbow joint set obliquely to the humerus but also to that of the forearm. As a rule the angles formed by the axis with the humerus and with the forearm are nearly equal, each measuring about 83°, both acute angles pointing outward. The styloid process of the ulna which marks the long axis of the forearm in both pronation and supination, deflects fully 14 degrees from the sagittal axis of humerus when the elbow is extended, and gradually approaches it as the elbow is flexed, for the angles of the humerus and of the forearm neutralize each other in the flexed position.
This study was made to test these results, and to determine the extent of the motion of the elbow in the European and in the negro, male and female, for during a number of years past I have felt conscious that a sexual difference exists.
In order to make satisfactory measurements fixed points had to be established and after extending Braune and Kyrklund's reliable method a modified method for measurement was hit upon which when applied repeatedly to the same arm gave an error of less than one degree. Unfortunately there are more variations than I had anticipated, but I venture to give my data with the hope that they may be of more general use, and that I may be able to add to them in the course of some years. To collect and measure 100 specimens is not altogether a small task, but this kind of work must be multiplied many fold before the foundations of anatomy — descriptive, regional and artistic — become anthropological.
The arms studied were taken from the dissecting rooms and carefully cleaned, leaving all of the ligaments of the elbow intact. Then the axis of the elbow was determined by fixing the ulna and radius, and moving the humerus to and fro. By doing this it is quite easy to find a point over each epicondyle which does not move. A line extending through these two points passes through the middle of the trochlea and marks the axis of the elbow joint. Frequently there is not an immovable point over one of the epicondyles, but instead a line is determined and in most cases the middle of the line is taken as the axis. Next the humerus was fixed with this axis and' a point in the middle of the upper third of the shaft in a horizontal plane 15 cm. above the plane of the table. The perpendicular plane was then passed through the middle of the upper third of the humerus and through the coronoid process, for it has been shown by Braune and Kyrklund that this process keeps within a millimeter of this plane, passing first to one side of it and then to the other. The screw motion which is said to be present by Meissner, Henke and Langer does not exist. Five centimeters from this plane a glass plate was fixed from which the measurements were taken. The horizontal
Franklin P. Mall
395
plane becomes a coronal plane when the arm hangs down along the side of the body, and therefore I still call it the coronal plane. In the same position the perpendicular plane is parallel with the sagittal plane of the body and may therefore be called the sagittal plane of the arm. The intersection of the two planes forms the axis of the humerus passing through the center of the upper third of the shaft and through the axis of the elbow below the coronoid process.
Diagram of the bones of the arm with the planes from which measurements were taken indicated. D, circle of maximum deflection of the ulna; d chord of the arc of deflection when the elbow is extended: d', the same at about 110 degrees; e, chord of the arc of extension when reduced to degrees to be subtracted from 180 degrees; f, chord by which the extent of the flexion of the elbow is measured.
The angle of the axis of the joint with the long axis of the humerus was first determined by direct measurement, the right arm being clamped with the humerus to my left, and the left arm in the opposite position. In all cases the degree of flexion, extension and deflection was determined by measuring from the styloid process of the ulna. The degree
396 On the Angle oi" the Elbow
of flexion was determined by the chord of the arc which would be described by moving the styloid process from maximum flexion to the long axis of the humerus with the axis of the elbow as the center. The degree of extension was determined by the chord of the arc described by the styloid process between maximum extension and the projected axis of the humerus. Accordingly when the elbow joint did not extend to a straight line or when it hyperextended this amount was respectively subtracted from or added to 180 degrees. The amount of deflection was determined for three positions measuring from the styloid process with the elbow flexed, extended and at 90 degrees. The degree is determined by the chord of the arc described by the styloid process intersecting the sagittal plane at right angles in these three positions named above. In case the deflection is out it is marked plus and in case it is in it is marked minus.
In the appended tables the first column gives the number of the cadaver. The second column gives the length of the ulna from the styloid process to the axis of the elbow joint. Next the angles of the humerus and the ulna with the axis of the arm are given. These, together with the degree of deflection of the forearm with the elbow joint extended to its maximum, always equal 180 degrees. Then follow the columns with the degree of motion, from maximum flexion to maximum extension, 180 degrees being a straight line. The lateral angle is next given in three positions and when it is marked minus it indicates that the arm turns in. This takes place frequently when the elbow is flexed to its maximum, occasionally when at right angles, and not at all when it is extended. In other words, when the arm is extended and supinated the whole wrist including the styloid process lies to the outward of a line drawn through the middle of the upper third of the shaft of the humerus and the coronoid process of the ulna. All arms are deflected laterally.
Braune and Kyrklund have shown conclusively that the elbow joint is a pretty perfect hinge joint and that there is practically no screw motion in it. As it flexes the ulna shifts a little, first outward then inward, which motion causes the shaft of the humerus to rotate outward nearly 6 degrees in case the forearm is flexed. For all practical purposes the joint is a hinge joint, the axis being set obliquely at nearly 8-t degrees to both humerus and ulna. In all cases the styloid process of the ulna deflects about 12 degrees when the arm is extended and when flexed because the angles of the humerus and ulna are about equal, the ulna lies in the sagittal plane of the humerus, i. e., the ulna comes to lie directly upon the humerus and not upon the chest as is claimed by Langer. In case the angle of the axis of the ulna is less than that of
Franklin P. Mall 397
the humerus, the styloid process still deflects when the elbow is flexed and in case it is greater it is turned in. Braune and Kyrklund's few ca^es (nine in number) seem to bear out these statements, but they are by no means always borne out by my records. The sigmoid cavity does not hug the trochlea closely and the slight rotation of the coracoid and olecranon processes may be sufficient to account for my figures. Furthermore, the inequalities in diameter and form of the two conical surfaces of the trochlea may cause sufficient shifting to counteract a slight difference between the angles of the humerus and ulna. This is already indicated when the points below the epichondyles through which the axis passes are determined. One of them is usually extended into a line several millimeters long showing that the section of the cone of the trochlea is not circular on that side. Even my averages do not confirm Braune and Kyrklund's notion. In my 89 specimens, the average of the angle of the humerus is 82.5 degrees, and of the ulna 86.5 degrees, and yet the styloid process still deflects .5 degree when the arm is flexed to the maximum. This, of course, is when the elbow is flexed to 39 degrees, and could it be flexed to the styloid process should turn in about 3 degrees. In general the irregularities of the surfaces of the elbow joint fully neutralize the fine difference between the angles of the humerus and ulna and only in a general way is the assertion of Braune and Kyrklund correct. In about three-fourths of my measurements the angle of the ulnais greater than that of the humerus, while in Braune and Kyrklund's measurements (but one-eighth as many) they w^ere just the opposite.
The extent of motion of the elbow from flexion to extension gires some interesting results. It is well known that the extent of movement in the joint of children is much greater than that of adults, and artists often try to express this in the arms of children and young, delicate girls^ I have often observed this difference in examining arms of infants in the dissecting rooms. In fact, in numerous specimens which I have examined not a single infant's arm was found in which the elbow could not be hyperextended. The measurements from the adult arm which I have made give equally interesting results, for they point towards a sexual difference. The following table gives the degree of extension of
Degrees of extension 155° 160' 165° 170° 175° 180° 185° 190° 195°
Number of males 1 6 19 14 14 6 3 1 ..
Number of females 2 6 7 5 2 1 2
Total 1 6 21 20 21 11 5 2 2
89 measurements. The straight arm is 180°. It is evident that the female arm is straighter and more frequently hyperextended than the
398 On the Angle of the Elbow
male. The degree of flexion gives a similar table, which becomes more
Degree of flexion 20° 25° 30° 35° 40° 45° 50° 55°
Number of males .. 3 17 23 17 3
Number of females 1 1 6 8 6 3 .. 1
Total 1 1 9 25 29 20 3 1
marked when it is expressed in differences, that is the degree of motion, from maximinn flexion to maximum extension.
Degree of motion .. . 110° 115° 120° 125° 130° 135° 140° 145° 150° 155° Number of males... 2
20°
125°
130°
135°
140°
9
«
15
11
12
1
2
4
8
Number of females..
Total 2 5 9 7 17 15 20 7 4 3
The two lines now move away from each other more than before, the greatest number of cases for each sex being 10° instead of 5° apart. In constructing this table the degree given is each time the middle figure; for instance, 130° includes 128° to 133°. Furthermore, there seems to be a slight racial difference which tends to make the sexual difference rather less marked than it really is. The greatest number of European males occurred in maximum extension under 170°, in maximum flexion under 35°, and in degree of motion under 135°. In other words, the motion of the elbow of the European male is more nearly like the female than the male negro. So when the joint of the negro alone is considered the sexual difference is more pronounced than when it is considered with that of the European. The following table
Degree of motion 110° 115
( Number of males. ... 1 5
Negro -^
I Number of females
Total 1 5 7 6 13 11 10 6 2 3
includes only the arms taken from negroes. On account of an insufficient number of records further tabulations give no results which are definite.
As far as the records go, they indicate that the elbow joint of the female is more flexible than that of the male — is more of the infantile type — and that of the European male holds an intermediate position between the negro male and negro female. Practically all of the subjects considered came from the laboring class, so a difference on account of muscular development cannot be entertained.
The amount of deflection of the forearm is shown in the data which follow. In all cases the styloid process deflects when the arm is extended
120°
125°
130°
135°
140°
145°
150°
155°
7
6
12
7
8
2
1
1
4
8
4
1
3
Franklin P. Mall 399
and every specimen verifies the statement of Langer and Briicke, that the whole wrist falls to the outside of the sagittal plane of the humerus when the forearm is extended and pronated. The assertion of Stratz that in this position the line falls in the middle of the wrist is absolutely incorrect. Furthermore, his diagram (Fig. 67) which is apparently based upon Merkel's normal figure, is also incorrect, for Stratz's own copies of Merkel's figures (Figs. 31 and 32), as well as the originals, coincide with Briicke's as regards this point.
With the elbow extended the average deflection of the styloid process of the ulna from the sagittal plane of the humerus is 11° from my measurements. The average length of the ulna from the axis of the elbow to the styloid process is 258 mm. With these two measurements 11° equals a chord about 5 centimeters long, so the styloid process deflects normally 5 cm. or about the width of the wrist. Therefore, with the arm extended the wrist should fall outside of the sagittal plane of the humerus in both supination and pronation. In both positions the styloid process falls about 5 cm. to the outside of the sagittal plane of the humerus and in pronation it passes through the styloid process of the radius. In the extended arm all of the wrist, or at least its greater part, falls lateral to the sagittal plane of the humerus in both pronation and supination. This marked deflection, more so in my records than is stated by any author, is no doubt due in part at least to a racial difference, for 70 of the arms are from negroes and but 19 from Europeans. A glance over the tables shows that some difference does exist, which I shall now consider. When the differences in deflection are grouped for every 5°, as was done when discussing the motion of the elbow, nothing definite is noted, and when they are grouped under single degrees the figures scatter so much that it is again difficult to see any marked result. The negro male, however, shows some 3° greater lateral deflection in the movement from flexion to extension than does the European male. The difference between the European male and female is much greater, but the number of cases are so few that this also cannot be considered. It would indeed be remarkable if more records showed that the European female had the greatest lateral deflection and that the European male the least, that of the negro lying between. If it should prove to be so, then artists have secured their ideal straight arm of females from the males and infants ' where the lateral deflection is the least.
The racial difference becomes more marked when the total amount of
' Braune and Kyrklund state that the angle of the humerus in infants is much less than in adults.
400 On the Augle of the Elbow
deflection (that is, the difference between that at flexion and that at extension) is divided by the number of degrees of motion of the elbow. The deflection being greatest in the negro male, the result becomes still greater because the motion of his elbow is the smallest. This quotient becomes the degree of lateral deflection for one degree of elbow motion. If this in turn is multiplied by 180, the amount of deflection is obtained, \n case the elbow joint could be moved from zero to 180 degrees. This quotient I shall spealc of as the total deflection, it being the amount of deflection in case the elbow joint had a motion of 180 degrees. For example, in the right arm of subject No. 925 the deflection is between — 4.5 degrees and 1 degree or 5.5 degrees. This divided by the number of degrees of motion (169 — 50) 119 makes .0462 or the number of degrees of lateral deflection of the forearm for each degree of flexion or extension. In turn this multiplied by 180 gives the total deflection could the forearm move through an entire semicircle. In this case it amounts to (.0462 X 180) 8.3 degrees. Now it is found that the deflection per degree varies for different positions of the forearm, as is shown in the following table. In the first column the deflection per degree is
Degree of deflection for each degree of motion from Race sex A rm ^^-i-^™ a""°" '"° '" ""'""" "TJf^^fvi^^^f/r "
iRigbit 08 Left 07 Both 075
[ Right 07
Female \ Left 075
{ Both 07
Both 075
C f Right 04
Male \ Left 025
( Both 0.3
r Right 11
Female \ Left 10
( Both 105
Both 05
Average 07 .085 .08
given between maximum flexion and 90 degrees, in the second from 90 degrees to maximum extension, and in the third the average degree of deflection for the whole motion of the forearm. Of course to determiue each figure it was necessary to start with an average. It is seen from the faille that the lateral deflection per degree of motion is generally less when the elbow is flexed less than a right angle than when it is extended beyond it. The deflections seems to increase as the maximum extension is approached. This is to be accounted for in part by the irregularity of
Negro
European
Extension
Extension
.10
.09
.08
.075
.10
.08
.09
.08
.08
.08
.085
.08
.09
.085
.07
.06
.055
.046
.06
.05
.10
.10
.05
.07
.075
.085
.075
.065
Franklin P. Mall 401
the surface of the elbow Joint. When the averages are considered it is seen that there is a marked difference between the deflection in the negro and in the European which becomes more pronounced when the males only are considered. The race of fully 70 per cent of the cadavers from which these arms were obtained can be determined by these measurements. The average deflection here is .08° and .05° for each degree of motian, and this difference is pretty constant, as can be seen from the table. The deflection between maximum flexion and maximum extension for negro males and European males is 10.5° and 6.50°, which, considering the differences in the lengths of the ulnas equals 5 cm. and 3 cm. respectively. If the total deflection is considered, that is, if the motion of the elbow were 180°, the deflection would be 14.5° and 9° for the negro and European respectively, which when the average lengths of the forearms are considered equals 6.5 and 4 centimeters. In a measure this difference is obscured for the flexed arm of the European deflects more than does that of the negro.
The conclusion of this study is that the degree of motion of the elbow is greater in the female than in the male and that the lateral deflection of the hand, from flexion of the elbow to extension is much greater in the negro than in the European. The lateral deflection of the hand in the extended arm is much greater than the artistic ideal.
Measurements.
Nearly all of the measurements are from arms taken from individuals belonging to the laboring classes. The American negro is more or less intermixed with European blood ; those in Baltimore are, however, usually over three-fourths black.
402
On tlic Angle of the Elbow
NEGRO, MALIC.
Right
Arm.
Angle of
axis Degree of movement
Lateral angles
of ulna in
of elbow.
joint,.
of ulna.
difl
erent positions
No.
Lencth of Ulna.
Humerus.
Ulna. Flexion.
Kxtension.
Maximum Kiirtit Flexion. Angle
Maximum . Kxtension
909
. . . 255
86
82 85
83 97 92
45 50 47
162.5
169
162
4.5
—8
5.5 — 1 —5
11
925
. . 270
1
956
. . . 260
3
1062
. . . 290
80
84
41.5
173
1.5
8
16
1072
, . . 268
67 76
87 83
100 90
88 94
33 35 35 43
165 176 175
168
— 7.5 — 1 3 —11
4
3
—6.5
13
1106
, . . 290
14
1126
. . . 270
5
1129
. . . 275
3
1136
. . . 265
75 84
94
84
43 48
168 180
—3.5 —3
3.5 .5
11
1142
. . . 240
12
1190
. . . 260
83 86 86 79
85 87
87 80 84 91
85 81
39.5
38
47.5
31
33
42
181 162 163 167 166 161
5 —1 2
4
3.5
2 7 1 9 5 7.5
10
1163
. . . 260
14
1172
. . . 280
10
1187
. . . 240
10
1190
. . . 290
10
1230
. . . 245
12
1261
. . . 275
85
82.5
39
170.5
3
5
12.5
1271
. . . 270
83
85
42
168
4
12
1275
. . . 265
82
. 87
40
167
—8
2
11
1285
. . . 275
81
94
39
162
— 4
5
1315
. . . 270
87
81
40
163
5
6
12
. . . 300
84
86
40
168.5
—3
1
10
. . . 285
83 82.5
85 87.5
44 40.5
155
167.5
—4 —1.3
2 2.6
12
Average (23) .
. . . 269.5
10
Len
A rm.
925
. . . 280
83
92.5
46
192
3
6
4.5
909
. . . 255
85
86
47
164
6
6
9
956
. . . 270
82 82
91
82
44 38
168 174
—8
—3.5
5
7
1062
. . . 285
16
1070
. . . 266
75
94
42
179
—7
11
1106
. . . 290
73 75
89 81
36 38.5
173 161.5
3.5 2.5
9 6
18
1123
. . . 250
14
1125
. . . 270
84 84
85 90
43 34.5
177 163
5 —3
7 1
11
1126
. . . 275
6
1128
. . . 290
83
88
40
170.5
6
4
9
1136
. . . 265
78 75 87 80
91 94
85 91
42 39 34 36.5
172 180 175
184.5
2 —3 2
3
4.5 1.5 — 1 6
11
1142
. . . 245
11
1155 . . . .
. . . 290
8
1157*
. . . 234
9
1187
. . . 240
90 85 79 83
82 84 85 81
45 46
41 44.5
158 167 184 173
—1.5
1
7.5
5
4
11.5
8.5
8
1190
. . . 260
11
1191
. . . 255
16
1208
. . . 230
16
1230
. . . 232
83
80
48
164
3
8.5
17
1261
. . . 278
85 85
80
85
36 37
164 167
6 2
8 3
15
1271
. . . 273
10
1275
. . . 270
83
86
38
173
—1
5
11
1285
. . . 285
86
91
36
166
1
3
1315
. . . 260
88
90.5
34.5
163
3
1.5
1.5
. . . 295
80 80
82
84 95
87
38.5
39
40
173 181 172
—16 .5
9.5
—7 4
16
. . . 255
4.5
Average (26) . .
, . . 265
10.5
Boy.
Franklin P. Mall
403
NEGRO, FEMALE.
891 270
1120 250
1141 265
1176 245
1188 238
1220 240
1221 240
1228 240
1272 240
1365 255
Average (10) 248
891 260
1120 245
1141 260
1166 237
1188 235
1220 243
1221 240
1228 245
1268 255
1272 240
1365 250
Average (11) 246
983 240
1123 245
1138 235
1140 270
1146 235
1258 255
1161 250
1286 250
1292 260
255
Average (10) 249.5
1146 230
1161 255
1195 270
1286 253
1292 265
Average (5) 255
1131 225
1225 225
Average (2) 225
1131 220
1225 223
Average (2) 221
Right
Arm.
83
83
46
184
—1
5
14
85
79
36
175.5
4.5
6.5
16
80
87
30
171
—2
5.5
13
85
85
32
177
2.5
2.5
10
80
88.5
40
180
—1
3.5
11.5
86
81
31
164
5
9
13
83
85
38
180
4
8
12
80
88
39
175
5
12
87
76
37.5
168
7
7
17
88
76
36.5
193
6
7.5
16
83.5
83
36.5
177
2.5
G
13.5
Left Arm.
79
90.5
43
182
—4.5
10.5
83
77.5
19.5
173
7
11
19.5
80
92
29
171
—3.5
2.5
8
85
87
27
170.5
4
4
8
80
92
35.5
180
—3.5
.5
8
80
83
29
173
7
13
17
83
86
41
174
3
6.5
11
75
94.5
36.5
175
— 4
1
10.5
80
91
30
179
—6.5
9
80
83
37
170.5
3
7
17
80
85
37
193
8.5
11.5
15
80.5
87.4
33
176.5
1
5.2
12.1
EUROPEAN, MALE.
Right
Arm.
83
88
41
172
—1.5
3
9
83
81.5
45
165.5
6
8.5
15.5
84
88
43.5
175
—9
—5
8
85
81
30
169
9
10
14
90
81
41
177
8
4
9
85
84
35
167
4.5
4.5
11
80
85
33
181
5
15
83
87
43
163
2
5
10
89
84
37
173.5
6
6.5
7
84
89
43
185
2.5
7
84.5
85 Left .
39 Arm.
173
2.5
4.5
10.5
87
89
40.5
173
8
6.5
4
75
87
57
166
6
9.5
18
83
84
33
171
7
7
13
80
93.5
35
172
—2
—1
6.5
85
84
31.5
169
5
8
11
82
87.5
39.5
170
5
6
10.5
EUROPEAN, FEMALE.
Right Arm. 77 90 37 183 82 88 44 175 79.5 89 40.5 179
82 83 S2.1
Left Arm. 87 40 85.5 40 86.5 40
188 167 177.5
-2.5
-4
-3.25
3
.5 1.7
2.5
1
1.75
6.5
13 10 11.5
11
11.5
11.3
40-i On the An-^lc of the Elbow
BIBLIOGRAPHY.
Brai'ne and Kyrkli'M). — Archiv fiir Anatomie, 1879.
Brucke. — Schonheit und Fehler der menschl. Gestalt. Wien, 1873.
DvRER. — Von der menschl. Proportionen. Niirnberg, 1527.
FicK.— Handbuch der Gelenke, 1904.
Fritsch. — Verhandl. der Berlin. Anthropol. Gesellsch., 1895.
Fritsch r. Harlass. — Die Gestalt des Menschens, 1879.
Hay. — The Geometric Beauty of the Human Figure Defined, 1851.
Henke. — Anatomie der Gelenke, 1S63.
Die Menschen des Michel Angelo im Vergleich mit der Antike. Rostock,
1892.
Hultkrantz. — Das Ellenbogengelenk. Jena, 1897.
KoLLMANN. — Plastische Anatomie. Leipzig, 1886.
Laxger. — Anatomie des Menschen, 1865.
Anatomie der ausseren Formen des menschl. Korpes. Wien, 1884.
Meissxer. — Zeitsch. fiir ration. Medicin, 1857.
Merkel. — Handbuch der Topographischen Anatomie, 1896.
Meyer. — Statistik u. Mechanik des menschl. Knochengeriistes, 1873.
Parson. — Jour, of Anat. and Physiol., 1900.
Potter. — Jour, of Anat. and Physiol, 1895
Quetelet. — Des proportiones du corps humain. Bull, de I'aead. royal des scien.. Belg., xv.
Richer. — Anatomie artistique, 1890.
Canon des proportiones du corps humain, 1893.
Sargent. — Scribner's Magazine, XIV, p. 130, 1893.
ScHADow. — Polyklet, oder die Maszen des Menschen nach dem Geschlechte, etc. Berlin, 1834.
Schmidt. — Proportionslehre des menschlichen Korpers. Tiibingen, 1882.
ScHMiD. — Arch, fiir Anthropologie, 1873.
Stratz. — Die Schonheit des Weiblichen Korpers. Stuttgart, 1900.
Welcker. — Archiv fiir Physiologie, 1875.
Zahn. — Bau und Mechanik d. Ellenbogengelenkes. Wiirzburg, 1862.
Zeising. — Neue Lehre von den Propositionen des menschl. Korpers, 1854.
Die Unterschiede in den Proportionen der Racentypen. Archiv fiir
Heilkunde, 1856.
Ueber die Metamorphosen in den Verhaltnisse der menschl. Gestalt
von der Geburt bis zur Vollendung des Langenwachstums. Verhandl. d. K. Leopold. Carolin. Akad. d. Naturforscher, XXVI.
A STUDY OF THE LOCATION AND ARRANGEMENT OF THE GIANT CELLS IN THE CORTEX OF THE RIGHT HEMISPHERE OF THE BONNET MONKEY (MACACUS SINI CUS).
BY
E. LINDON MELLUS.
From the Anatomical Laboratory of the Johns Hopkins University.
With 3 Figures.
In view of the recent experimental results regarding the representation of movements in the cerebral cortex, a more exact study of the distribution of the large pyramidal cells as seen in microscopic sections has seemed to me desirable. The following paper deals with the distribution in the bonnet monkey.
The right hemisphere of a healthy adult monkey (Macacus sinicus) hardened in Miillers fluid, dehydrated and imbedded in celloidin, was cut in horizontal sections 50 microns thick. The sections were numbered from below upward, and stained first by Pal's modification of Weigert's hematoxylin method, counter-stained with - carmine and mounted in balsam. This double stain has the advantage of accentuating the contrast between cells and fibers and facilitating the study of the relation of the cells to the various fiber tracts.
A careful study of these serial sections reveals the following arrangement of the Betz (giant) cells in the motor cortex and, if confirmed by the study of their disposition in other specimens, may lead to some modification of the present ideas in relation to the extent of the so-called " motor areas of the cortex.
On the external surface of the hemisphere the lowest point at which any giant cells are found corresponds to the lower extremity of the fissure of Rolando. A few scattered cells are found here upon the anterior lip, but quite in the depth of the fissure. From this point upward they gradually increase in number and at a point about 0.5 mm. higher up there is a small group of giant cells between the corona radiata of the ascending frontal convolution and the surface, but the majority of these cells is still within the fissure contiguous to what may be called the posterior aspect of the corona radiata of the ascending frontal con American Journal of Anatomy. — Vol. IV.
406 Giant Cells of tlie Bonnet Monkey
volution. Another small group of giant eells appears in a corresponding position, after an interval of 10 sections (0.5 mm. higher on the surface) contiguous to the external aspect of the corona radiata of the ascending frontal convolution. This arrangement of the giant cells in groups does not obtain within the fissure of Rolando, but they appear here as a continuous layer in gradually increasing numbers from below "upward. Xor is there any further appearance of grouping of the giant cells on the external aspect of the corona radiata of the ascending frontal convolution, but from this point upward they extend farther and farther forward until in the level of the anterior limb of the frontal sulcus they cover the entire antero-posterior extent of the external aspect of the corona radiata of the ascending frontal convolution. At a slightly higher level the giant cells entirely envelope this process of the corona radiata ; that is, they are present upon its posterior, external and anterior aspects, and as we reach still higher levels extend a short distance forward in contiguity with the external surface of the corona radiata of the frontal lobe (Fig. 3).
This arrangement is maintained throughout the remainder of the upward extension of the corona radiata, which, in the monkey, corresponds to the cortex of the ascending frontal and the posterior portion of the superior frontal convolution (Fig. 1).
This distribution of the giant cells upon the external surface of the brain is by no means uniform. They are most numerous within the sulcus of Eolando and in that portion of the cortex covering the ascending frontal convolution, while in the cortex of the superior frontal they are more Scattered. Within the sulcus of Eolando they extend to the base of the sulcus, but are confined entirely to the anterior lip; that is, they nowhere pass beneath the base of the fissure to the parietal lip.
There are two small groups of large cells in the cortex of the ascending parietal convolution : one just above the lower extremity of the intra-parietal fissure appearing in fourteen consecutive sections, the cells diminishing in number and size from below upward. These cells extend into the intra-parietal fissure but not into the fissure of Rolando. There is another small group of large cells in the cortex of the upper ■extremity of the ascending parietal convolution, only present in four sections. With the exception of a few very large cells within the intraparietal fissure, the cells described in the cortex of the ascending parietal convolution are much smaller than the majority of the giant cells anterior to the fissure of Rolando. Those anterior to Rolando measure from 20 to 60 microns in length bv from 10 to 40 microns in
E. Lindon IMellus
407
FiP-l.
F
DISTRIBUTION OF GIANT CELLS (BETZ) IN CORTEX OF BRAIN (MELIUS). 32
408 Giant Cells of the Bonnet Monkey
breadth, while those in the cortex of the ascending parietal convolution, with the exception noted, are from 15 to 22 microns long by 12 to 18 microns wide.
On the mesial surface of the brain the superior border of the cortical area in which the giant cells are found corresponds exactly with the superior border of that upon the external surface; that is, the anterior and posterior borders of this area may be followed directly over from the external convex surface of the brain upon the mesial surface. The area occupied on the mesial surface is a somewhat irregular triangle with its apex corresponding to the upper extremity of the fissure of Eolando and its base directed toward the frontal pole. The giant cells are relatively more numerous upon the mesial surface. Instead of being arranged in a single layer, as upon the external surface, they are more irregularly scattered about in groups of several superimposed layers. Cells of the larger diameters are also relatively more numerous on the mesial than on the external surface. The area extends downward to the calloso-marginal sulcus about 8 mm. below the crest of the hemisphere. The cells in the lower portion of this area are less numerous and rather smaller than elsewhere on the mesial surface.
EXPLANATION OF FIGURES. Note that, for the sake of comparison, Fig. 3 is placed above Fig. 1.
Fig. 1. External surface of right hemisphere; R. Fissure of Rolando; 8. Fissure of Sylvius; F. Frontal pole"; 0. Occipital pole; AB. Plane of section of Fig. 3. Area of distribution of giant cells is striated.
Fig. 2. Mesial surface of right hemisphere. C. Calloso-Marginal sulcus; F. Frontal pole; 0. Occipital pole; AB. Plane of section of Fig. 3. Area of distribution of giant cells is striated.
Fig. 3. Horizontal section at line AB, Figs. 1 and 2, showing- arrangement of giant cells at that level. R. Fissure of Rolando; F. Frontal pole; 0. Occipital pole.
Gage SP. A three weeks' human embryo, with especial reference to the brain and nephric system. (1905) Amer. J Anat. 4: 409-443.
