Talk:Paper - The phylogenetic relations of the lymphatic and bloodvascular systems in vertebrates (1910): Difference between revisions

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We thus reach the end-link in the long chain of successive diflferentiations which lead through the vertebrate series to the final stage in which the greatest attainable degree of independence between lymphatic and haemal vascular structiu*e has been reached, and in which the primitive relative value to the organism of the two systems has been reversed, in obedience to the law which has stamped the bloodvascular system as the main organic line of evolutionary progress.
We thus reach the end-link in the long chain of successive diflferentiations which lead through the vertebrate series to the final stage in which the greatest attainable degree of independence between lymphatic and haemal vascular structiu*e has been reached, and in which the primitive relative value to the organism of the two systems has been reversed, in obedience to the law which has stamped the bloodvascular system as the main organic line of evolutionary progress.
==PANCREATIC BLADDERS==
WILLIAM SNOW MILLER Fmm the Anatomical Laboratory of the University of Wisconsin
For several years I have not given the course in mammalian anatomy which forms part of the work introductory to the study of human anatomy, at the University of Wisconsin, louring the summer session of the present year (1909) it fell again to my lot to give this course, and one of the animals used presented a variation not unusual in our laboratory, a pancreatic bladder.
In two earher communications I have called attention to the occurrence in the domestic cat of a pancreatic bladder which bears a similar relation to the pancreatic ducts that the gall bladder does to the bile ducts.
With the description of the present case there are now on record seven cases in which this peculiarity was present and of the seven cases, five have been found in the anatomical laboratory of the University of Wisconsin. The first case was described by Mayer in 1815, a second by Gage in 1879, three cases by myself in 1904 and a fourth case in 1905.
That five of the seven cases should be found in a small community seems to indicate, either that there exists locally a special breed of cats, or that there has been a lack of careful observation on the part of those instructors whose courses include the dissection of the cat.
It is not improbable, however, that some cases of a pancreatic bladder have been overlooked, having been mistaken for cases in which a double gall bladder was present.
It is my custom when students take up the study of the viscera of the cat, to inject with a different colored starch mass the bile ducts and the pancreatic ducts. This is easily done by making an opening in the duodenum 25 to 30 mm. in length opposite the
16 WILLIAM SNOW MILLER
entrance of the ductus choledochus, thus exposing the oval opening leading into the ampulla of Vater. With but little diflSculty a cannula can be inserted and tied in the ductus choledochus and the injection of the bile ducts and gall bladder completed. It often requires some skill and patience to introduce a second cannula by the side of the first into the ductus pancreaticus; but the technique once acquired, rarely does anj'^ diflSculty present itself.
By this simple procedure the student is able to follow the gross distribution of the bile and pancreatic ducts and, as I usually inject the arterial system, the systemic veins and the portal system witli still diflferent colored masses, the relation which these ducts bear to the blood vascular system is easily made out.
The case I now record was found in a young male cat obtained from a part of the city far removed from that of the preceding cases; therefore it seems quite improbable that this cat was in any way related to the others.
The type is that of the second and third cases that I have desscribed, namely, a duct leading from the duodorsal division of the ductus pancreaticus and terminating in a well-defined bladder situated a httle to one side of and dorsal to the gall bladder, which occupies its usual position in the right median lobe of the liver. It dififers from the other cases in that there is a triangular flap of pancreatic tissue surrounding the entrance of this duct into the duodorsal division of the ductus pancreaticus. Because of this peculiarity the present case occupies a position between the second case described by Heuer (see below) and the cases previously described by myself. The relations of the various parts are shown in fig. 1.
The question as to the origin of these pancreatic bladders at once presents itself, and in this connection it is interesting to note two variations of the pancreas found by Heuer while studying the arrangement of the pancreatic ducts of the cat.
In the first case (fig. 2) a band of glandular tissue, an outgrowth from the caput, passed cephalad, following the ductus choledochus and cystic duct and partially covering them on their ventral side. It extended to
PANCREATIC BLADDERS 17
about the middle of the gall bladder, where it fused with the connective tissue around the latter. It had a duct which passed down its entire length and joined the axial branch of the caput. In the second case (fig. 3) a similar though slightly narrower band of glandular tissue extended from the caput alongside of the ductus choledochus and ductus cysticus. It then continued along the left side of the gall bladder to the posterior (ventral?) part of the liver, where it enlarged into an oval
Fig. 1. Drawn in situ. Shows the relation of the pancreas and the pancreatic bladder to the liver, stomach and duodenum. The liver has been turned cephalad; the stomach is in outline.
G. B., gall bladder; R. L., right lateral lobe of the liver; L. L., left lateral lobe of the liver; P. B., pancreatic bladder; P., pancreas; D., duodenimi.
The triangular flap of pancreatic tissue mentioned in the text can be seen extending from the pancreas along the duct connected with the pancreatic bladder. One-half the natural size.
nodule about one centimeter in its long diameter. This nodule occupied a hollow in the right central lobe of the liver to the left of the gall bladder. A duct was present which extended from the nodule down the middle of the band, and joined the axial branch of ihf caput as in the previous case.
The pancreas is usually described as arising from a dorsal and a ventral anlage which fuse after rotation of the duodenum has taken place, the ventral anlage giving rise to the ductus pan
18
WILLIAM SNOW MILLER
creaticus (Wirsung) while the ductus accessorius (Santorini) takes its origin from the dorsal anlage.
In cyclostomes and selachians a dorsal anlage only is present, in all the remaining vertebrates a dorsal and ventral anlage is found and the investigations of Stohr, Goppert, Saint-Remy, Felix, Hammer, Stoss, Wlassow, and others have shown that the ventral anlage is paired, a pancreatic diverticulum arising on
Fig. 2. Schematic drawing constructed from Heuer's description of his first case of a pancreas with three principal divisions.
D., duoaenum; G. B., gall baldder; R. L., right lateral lobe of the liver; L. L., left lateral lobe of the liver; P., pancreas with a band of pancreatic tissue extending along the ductus choledochus.
each side of the liver stalk. The left ventral outgrowth usually disappears, the right persisting and maintaining its association with the liver stalk which now becomes the ductus choledochus. Returning now to the cases of Heuer: it seems probable that in each case both the right and left ventral anlage persisted, the left in case one (fig. 2) giving rise to the broad band of pancreatic tissue extending along the ductus choledochus and ductus cysti
PANCREATIC BLADDERS 19
cus, while in the second case (fig. 3) the left anlage was drawn out into a long narrow band with an enlarged distal end. Now if we conceive the narrow band of pancreatic tissue in the second of these cases to undergo a degeneration leaving only the duct, and the distal enlarged portion converted into a dilatation, we have a complete series of changes through which these pancreatic bladders may have arisen.
Fig. 3. Outline drawing of Heuer's second case of a pancreas with three principal divisions.
D.. duodenum; G. B., ^all bladder; R. L., right lateral lobe of the liver; L. L., left lateral lobe of the liver; P., pancreas with a long narrow band of pancreatic tissue extending along the ductus choledochus and terminating in an expansion situated on the left side of the gall bladder. (After Heuer.)
Another and more probable hypothesis may be advanced, namely: that the ventral anlage, in place of being double, may in these cases be bi-lobed, either from the beginning, or as a result of fusion, one of the lobes having given rise to the caput of the pancreas and the other to the bands of pancreatic tissues found by Heuer, or to the pancreatic bladders which I have found.
20 WILLIAM SNOW MILLER
That the ventral anlage is in some cases bi-lobed, the investigations of Wlassow on the development of the pancreas of the pig have shown.
I have described this additional case of a pancreatic bladder and suggested two possible explanations of the origin of these bladders in order that attention may again be called to the anomaly and to the embryological questions involved, and to stimulate more careful observation on the part of those who give courses in mammalian anatomy.
LITERATURE
Fblix, Wai/teb. Zur Leber- und Pancreasentwicklung. Arch, f . Anat. u. Phys.
1892. Anat. Abt.
Qagb, S. H. The Ampulla of Vater and the Pancreatic Ducts of the Domestic Cat.
1879. Amer. Quart. Mic. Jour. vol. 1.
GOppebt, Ernst. Die Entwickelung und das spfttere Verhalten des Pancreas der
1891. Amphibien. Morphol. Jahrb. Bd. 17.
1893. Die Entwicklung des Pancreas der Teliostien. Morphol. Jahrb.
Bd.20. Hammab, J. Aug. Einige Plattenmodelle zur Beleuchtung der fOheren embrionalen
1893. Leberentwicklung. Arch. f. Anat. u. Phys. Anat. Abt.
Heueb, Q. J. The Pancreatic Ducts in the Cat. Johns Hopkins Hosp. Bull. vol.
1906. 17.
Mater, A. C. Blase fOr den Saft des Pancreas. Arch. f. Anat. u. Phys. Bd. 1
1815. Miller, W. S. Three Cases of a Pancreatic Bladder Occurring in the Domestic Cat.
1904. Amer. Jour, of Anat., vol. 3.
1905. A Pancreatic Bladder in the Domestic Cat. Anatom. Abe. Bd. 27. Saint-Rbmy, Q. Recherches sur le d^veloppment du pancreas chez les Reptiles.
1893. Joum. de Panat. et de la physiol. Ann^e 29.
St5hr, Ph. Die Entwicklung von Leber und Pancreas der Forelle. Anatom. Anz.
1893. Bd. 8. Stoss. Zur Entwicklungsgeschichte des Pancreas. Anatom. Anz. Bd. 6.
1891. Wlassow. Zur Entwicklung des Pancreas des Sohwein. Morphol. Arb. Bd. 4,
1895.
AN ADULT HUMAN PANCREAS SHOWING AN EMBRYOLOGICAL CONDITION
W. M. BALDWIN Cornell University Medical College
This unusual pancreas was removed from the body of an adult white female, 71 years old, who had died of "valvular heart disease. The abdominal cavity presented a number of anomalous conditions, among these an abnormal duodenum and pancreas. The duodenum, which was of the V-shaped variety, presented an ascending limb lying to the right of and ventral to the descending limb.
D. PANC ACC.
OUOOENUM
D. CHOL
0. PANC.
The pancreas, represented in the figure as seen from the dorsum, consisted of two parts luiited with each other by a narrow strand of glandular tissue dorsal to the duodenum. The larger por
22 W. M. BALDWIN
tion lay ventral to the bodies of the first and second lumbard vertebrae upon the left side of the descending limb of the duodenum.
Because of the pecuUar V-shape of the duodenum this portion of the pancreas was not situated within the loop nor did it have any relation to the transverse or ascending portions of the duodenum. It lay dorsal to the stomach and extended a distance of only 5.0 cm. towards the left kidney possessing a cephalocaudal diameter of 3 cm. and a maximum thickness of 1.3cm. Traversing themiddle of the glandular sustance, a single large duct passed with increasing calibre from left to right finally emptjdng into the duodenum 4.0 cm. caudal to the pylorus.
The other smaller portion of the gland lay dorsal to the duodenum and on a level slightly caudal to the part just described. Its long axis .extended along the conmion bile duct, which traversed it ventrally, a distance of 3.0 cm. with a width of 2.0 cm. and a maximum dorso-ventral dimension of 1.5 cm. Coursing through this tissue a single small duct passed caudally to empty finally upon the dorsal wall of the duodenum in company with the common bile duct. This duct approached the caudal aspect of the latter. The narrow band of pancreatic tissue which joined both portions of the gland was drained by radicles of both ducts, yet the ducts were not in communication with each other. Upon the duodenal mucosa, the openings of the ducts were separated by an interval of 3.5 cm., the duct from the larger portion being cephalic and ventral.
This anomaly seems to be an instance of the non-fusion of the primitive ventral and dorsal pancreatic anlages, together with an insufficient "rotation" of the ventral anlage around the duodenum. The dorsal portion of the gland in close apposition to the common bile duct corresponds to the ventral anlage which forms ultimately the caudal portion of the head of the adult pancreas and the terminal portion of the main pancreatic duct. The larger portion, derived from the dorsal anlage, represents the remainder of the head and all of the neck and body of the gland together with the enclosed ducts.
Received for publication, November 20, 1909,
===The Early Histogenesis Of Striated Muscle In The (Esophagus Of The Pig And The Dogfish===
Caroline McGill
Instructor in Anatomy, University of Missouri With Twenty-Five Figures
Striated muscle is described by most investigators as coming exclusively from the inner plate of the myotome. In the later development of the tissue each muscle fiber is usually said to arise from a single myoblast. Neither of these statements holds good however, regarding the oesophagus of at least the two forms studied, as will appear from the following description of the early development. A brief review of the literature on this subject will first be given.
LITERATURE REVIEW
The literature, for convenience, is here divided into three classes: (1) the papers which describe the origin of striated muscle in general from the germ layers; (2) those which describe the transformation of the myoblasts into muscle fibers; and (3) those which describe the histology of the adult oesophageal muscle.
(1) Vertebrate striated muscle, with the exception of one of the inner eye muscles of the chick, is almost universally described as arising from the mesoderm. Herzog ('02) found that in the chick the sphincter of the pupil develops from ectoderm. The mode of transformation of mesoderm into muscle-forming tissue (pre-muscle, as it is termed by Lewis '01) is disputed. The three early derivatives of the mesoderm, the myotome, the mesothelium and the mesenchyme, each have been considered bj'^ various writers to be the muscle-forming tissue. For a complete review of the literature on this subject the reader is referred to the paper by Maurer, Die Entwickelung des Muskelsystems und der elektrischen Organe, — ^in the Hertwig's Handbuch d. Entwickelungs
24 CAROLINE MCGILL
lehre der Wirbeltiere, Bd. 3, (1906). Remak ('55) and Balfour C85) believed that striated skeletal muscle is derived from both the outer and inner plates of the myotome. The Hertwigs ('81) in Selachians, Minot ('92) in the frog, Godlewski ('02) in the rabbit, mouse and guinea-pig, Dahlgren and Kepner ('08) in Catostomus, with many other investigators, found striated muscle arising exclusively from the inner plate of the myotome. The head muscles have usually been described as arising from the epithelium of the head somites (Marshall, '82, in Selachians), but Renter ('98) found that in the pig the outer eye muscles develop from the head mesenchyme.
Lewis and Bardeen ('01) stated that in the human embryo '*The skeletal and muscular structures of the limbs are differentiated from the mesenchyme of the limb buds." Lewis ('01) discovered that in the arm of the human embryo the muscle develops directly from mesenchyme. He gives a good review of the literature on the origin of the limb muscles, to which the reader is referred. Since Lewis' paper appeared, Ingalls ('07) has described the origin of the limb muscles from the outer layer of the myotomes in a 4.9 mm. human embryo.
Mlodowska ('08) studied the development of striated muscles in the chick, mouse, rabbit, and pig, and found that most of the skeletal muscle arises from muscle plates, but that the surrounding mesenchyme aids in the later formation.
(2) There are two general theories advanced to account for the origin of the multinucleated striated muscle fiber from the undifferentiated muscle tissue. One is that each primitive myoblast develops into a single muscle fiber, the other is that several myoblasts fuse to form the muscle fiber. The latter is the syncytial theory of muscle origin. Remak ('50- '55), KoUiker ('51), Schultze ('61), Hertwig-Mark ('92), Minot ('92), Bardeen ('00), Eycleshymer ('04), Maurer ('06), and Dahlgren and Kepner ('08), adhere to the unicellular origin of the muscle fiber. Maj^o ('62), Calberla ('76), Marchesini, and Ferrari ('96), Godlewski ('02), Mlodowska ('09) and numerous other writers, claim that the muscle fiber is of syncytial origin. The syncytium, most of these investigators believe, is formed by a secondary fusion of
HI8TOGEN8IS OF STRIATED MUSCLE 25
independent epithelial myoblasts. Bom (73), Calberia ('76), Minot ('92), and Maurer ('06) give complete reviews of the literature, so a rfeum^ of the papers of earlier investigators is unnecessary.
(3) The structure of the muscle of the adult oesophagus. Oppel ('97) gives a lengthy review of the Uterature on the structure of the muscle of the vertebrate oesophagus, to which the reader is referred. Since the structure of the adult muscle throws some light on the development, a short review of a few of the papers is given here. According to Oppel, all of the muscle of the oesophagus of amphibia, birds, and reptiles is smooth. In most fishes and mammals, a marked differentiation of smooth into cross-striated muscle has taken place. In some of the fishes both layers of muscle are striated throughout the length of the oesophagus; in other fishes only one layer, usually the thicker inner one is striated. Mammals also have varying amounts of striated muscle. In ornithorhynchus, all of the muscle in both layers is smooth, just as in amphibia, reptiles and birds. In a niunber of mammals (giraffe, elephant, all rodents, cattle and sheep) both layers of muscle are striated down to within onefourth inch from the cardia. In some manunals striated fibers of the outer or longitudinal layer have been described as extending for a distance upon the cardia. Between these two extremes are all transitions.
Oppel states also that the primitive vertebrate probably possessed only smooth muscle in the oesophagus. The presence of striated muscle where it does occur, he thinks is due to a downgrowth of the muscle of the pharyngeal constrictors upon the oesophagus. He thus derives the striated oesophageal muscle from the branchial muscle \yhich is held by most investigators to arise from the lower head myotomes.
Coakley ('92) describes striated muscle fibers in the upper part of the human oesophagus as having a structure precisely like that of the skeletal muscle. In the lower oesophagus he found scattered striated fibers in both layers extending as far as the stomach. These lower fibei's do not show as distinct crossstriations, as do the ordinary striated muscle fibers. He believes
26 CAROLINE McGILL
that they are an intermediate form between smooth and crossstriated muscle. Though not so stated, he evidently thinks that the striated muscle here is formed directly from the smooth muscle.
Flint ('07) worked only on the grosser structure of the oesophagus of the pig embryo. The striated muscle is formed, he states, by differentiation of the mesenchyme. In the 13 nam. pig embryo the mesenchyme cells have begun to elongate. By the time the embryo is 7.5 cm. long, both layers of muscle are differentiated. The first evidence of cross-striation appears at 11 cm.
The writer ('07) in a description of the development of smooth muscle in the oesophagus of the pig, found the striated muscle developing somewhat earlier than described by Flint. There is an elongation of mesenchyme cells to form the circular layer beginning in the mid-oesophagus of the 5 nam. pig. In the 8 mm. embryo the elongation of cells extends the entire length of the oesophagus. From this differentiated mesenchyme, in the upper and mid-oesophagus, striated muscle develops; in the lower oesophagus, smooth muscle.
MATERIAL AND METHODS
The oesophagus of the dogfish (Acanthias vulgaris) and of the pig was the material used. Serial sections of dogfish embryos from 3 mm. to 60 mm. in length were studied. The embryos from 3 mm. to 10 mm. long were fixed in Zenker's fluid. All the longer ones were fixed in sublimate or in sublimate-acetic solutions. The pig embryos used ranged from 4 mm. to 60 mm. in length. Thej'^ were all fixed in Zenker's fluid and were cut in serial sections. All were embedded in paraffin. The sections were stained in Delafield's haematoxylin, Heidenhain's iron-hsematoxylin with a counter stain of Congo red, and in Mallory's aniUn blue connective tissue stain.
OBSERVATIONS
This paper is restricted to the early development of striated muscle in the oesophagus. The later development, including the differentiation, growth, and multiplication of the fibers, is reserved for a separate paper.
For tracing the origin of the myoblasts, dogfish embryos were used. The later transformation of myoblasts into muscle fibers was studied chiefly in pig embryos.
(1) The Origin oi Myoblasts in the (Esophagus
As already mentioned in the literature review, Oppel ('97) found the striated muscle of the oesophagus to be a downgrowth of pharyngeal muscles, hence arising indirectly from the myotomes of the branchial region. Flint ('07) and the writer ('07) state that it arises from the mesenchyme surrounding the endodennal tube.
In both dogfish and pig embryos, the oesophageal striated muscle arises directly from the mesenchyme. There is apparently no downgrowth from the pharyngeal region, at least in the dogfish. To be sure of this it was necessary to study early embryos and to trace the development of the mesenchjine cells in which the muscle arises. This was done in the dogfish material.
The earliest dogfish embryo studied by the writer was 3 mm. in length. At this stage there are very few mesenchyme cells formed. The mesoderm is represented by two layers, the somatic and splanchnic, which have extended dorsalward and form a number of myotomes. In places in the head region from the splanchnopleure at its jimction with the myotome, a few irregular cells seem to be arising, which may represent the first mesenchymal 'Cells. Minot ('92) stated that the mesenchyme arises solely from the mesothehum, the cells leaving the mesothelium, but remaining connected with it and with each other by protoplasmic processes. Thus from its origin the mesenchyme is a syncytium. He also found that the first mesenchyme of elasmobranchs arises from the splanchnic layer at the point where the myotome unites with the nephrotome.
Fig. 1. is a crossHBection through the upper oesophagus of a 3 mm. dogfish embryo. There is nowhere in this embryo any distinct mesenchyme formed. At a in fig. 1. is a stellate cell which seems to have formed from the mesothehum, and is still connected with it by protoplasmic bridges. It may be one of
28 CAROLINE MCGILL
the earliest mesenchyme cells. The mesotheUal cells at this time have numerous processes which extend to the surroimding organs. Fig. 4 is a high power drawing of area X in fig. 1, and shows these processes distinctly. They are most numerous dorsal and ventral to the coelom.
Fig. 2 is drawn from a section near the mid-oesophagus of the same 3 mm. embryo. The myotomes are shown connected with the coelomic mesotheUum by a narrow strand of irregular cells. Under high power (fig. 5) these cells are found to be connected by wide anastomoses, and from them numerous processes extend to the ectoderm and the endoderm. They have much the appearance of mesenchyme cells, but sections of a later embryo at this region show that no true mesenchyme has yet been formed.
Fig. 3 is through the lower oesophagus of the same embryo as shown in figs. 1 and 2. At this point the two layers of the mesothehum are distinct and the coelomic cavity extends into the myotome. Fig. 6 is a high power drawing of area X in fig. 3. There are wide protoplasmic anastomoses between the two layers of mesothelial cells, and many finer processes extend to the basement membranes of the ectoderm and the endoderm. In the 3 mm. embryo the myotome is in contact with the epithelium of the oesophagus, but a study of later stages shows that before the mesenchyme, which later surroimds the oesophagus, is formed, the myotomes have grown some distance dorsalward and are well removed from the oesophagus. At a later stage, also, most of the protoplasmic processes of the mesothelial cells have been withdrawn, so it is probable that they do not represent the anastomoses of the later mesenchymal syncytium.
Since syncytium, as used in recent anatomical writings, has had various meanings, its definition as here employed is given. By syncytium is meant any tissue where there are well defined protoplasmic anastomoses between the cells. Where all the cells are so united, the tissue is described as a complete syncytium. Where some of the cells are independent and others are connected, the term partial syncytium is used. By cell, as employed in describing a syncytium, is meant merely the irregular stellate or spindle shaped mass of protoplasm which makes up a nodal
HISTOGEN8IS OF STRIATED MUSCLE 29
point of the protoplasmic network, together with the enclosed nucleus.
In the 4 mm. dogfish embryo the coelomic epithehum has grown far forward beyond the region of the oesophagus; and from it, around the brain and upper pharynx, considerable mesenchyme is forming by the outgrowth of stellate cells from the mesothelium. In the neighborhood of the oesophagus, the condition is almost precisely as in the 3 mm. dogfish, with the exception that the myotomes have grown farther dorsalward.
Fig. 7 is from the upper oesophagus of a 5.5 mm. dogfish embryo. Here the myotome is well formed and has grown well away from the endodermal tube. The mesothelium is distinctly epithelial and shows fewer cytoplasmic processes than were present in the 3 mm. embryo. Though no mesenchyme is yet present in this region, it is well formed as a complete syncytium filling in the spaces between the organs in the head region.
Fig. 8 is from the mid-oesophagus of the same embryo as shown in fig. 7. Here there are a few stellate cells between the splanchnic layer of the mesoderm and the endoderm, but the high power drawing (fig. 9) of area of X in fig. 8 shows that most of these loose cells are really endothehal cells. The blood vessels are growing in at this stage.
In the 10 mm. dogfish embryo there is the first distinct formation of mesenchyme between the splanchnopleure and the endoderm of the oesophagus. The splanchnic mesothelium is closely applied to the endoderm and also extends as a mesentery to become continuous with the somatic layer. The enlargement of the coelom brings about this condition as shown in fig. 10. At this stage the oesophagus is more definitely separated from the myotome and from the mesenchyme, mc. In the uppermost part of the oesophagus near the pharjnix there is a very small amount of mesenchyme, continuous with the head mesenchyme. Longitudinal sections of this region show nothing that can be identified as cells of myotomic origin. The mesenchyme here comes from the splanchnopleure. At A in fig. 10, mid-oesophagus, is a spindle-shaped mesenchyme cell between the endoderm and the mesothelium Fig. 11 is a high power drawing from a section of
30 CAROLINE McGILL
the same embryo, slightly anterior to the one from which fig. 10 was taken. This section shows the origin of two mesenchyme cells from the mesothelium.
In fig. 12 is shown the mid-oesophagus of a 25 mm. dogfish. This is at the region where the limien of the oesophagus is obliterated for a time. In sections both above and below the one pictured no lumen is present. Here quite a thick layer of mesenchyme has differentiated from the mesotheliimi. Longitudinal sections show that this mesenchyme forms in situ. There are no indications that its cells migrate from the myotomes, from which the oesophagus is now completely separated. Longitudinal sections show that in the upper oesophagus little or no mesenchjrme has yet appeared.
The mesenchyme cells of the oesophagus form a complete syncytiiun. They are still connected by wide anastomoses with the mesothelium. From this time on, most of the new formation of the mesenchyme of the oesophagus in this region is by the mitosis of the cells already formed, and not by further differentiation from the mesothelium. In the mesenchymal syncytium of the mid-oesophagus the cells soon begin to differentiate into myoblasts, as shown in Fig. 13.
Pig embryos were not obtained young enough to trace the early formation of the myoblasts. When first studied in a 4 mm. pig embryo, the oesophagus and surrounding region show about the same structiure as seen in the 25 mm. dogfish embryo (fig. 12). In the 4 to 7 nun. pig embryos the oesophagus is surrounded by a thick layer of undifferentiated mesenchyme. There is no indication of a migration of myoblasts from the myotomes into this tissue. As we have seen, it seems highly probable from the study of the early dogfish embrj'o that the myoblasts of the oesophagus arise from the mesenchyme derived from the splanchnopleure, not from the muscle plate, and that there is no downgrowth of the pharyngeal muscle to form oesophageal muscle. The same condition is probably present in the pig embryo.
(2) The Transformation of the Mesenchyme into Crossstriated Muscle
(a) Early Development
In the dogfish mid-oesophagus, until the embryo reaches a length of 26 mm., and in the pig embryo until it reaches 5 mm. the tissue outside of the endodermal tube consists of a loose mesenchjTnal syncytium, the origin of which has just been described. The nuclei of the syncytium are round or oval with distinct nuclear wall and chromatin reticulum. From one to three true nucleoli are present in each nucleus, but they are frequently obscured by the chromatin. The protoplasm shows a reticular structuie, the strands of which are made up of fine granules (fig. 12 from a 30 mm. dogfish embryo, and fig. 15 from a 7 nmi. pig embryo).
In this mesenchymal syncytium throughout the entire length of the dogfish oesophagus, and in the upper two-thirds of the pig oesophagus, striated muscle develops. In the lower third of the pig oesophagus smooth muscle develops. The first stage in muscle formation is a general condensation of the mesenchyme at a short distance from the endodermal tube. This begins in the 4 mm. pig embryo, and in the 25 mm. dogfish embryo. The condensation is brought about by a rapid mitotic division of the nuclei, with a corresponding increase in the amount of syncytial cytoplasm. The condensation begins in the mid-oesophagus and extends rapidly both up and down the tube.
The early formation of striated muscle in the oesophagus of both pig and dogfish up to the time the cross striations appear in the fibrillae, is precisely like the development of the smooth muscle of the lower oesophagus of the pig. The two tissues arise from a continuous sheet of mesenchyme. The description given in the writer's paper on the histogenesis of the smooth muscle in the oesophagus of the pig (McGill '07) will therefore apply equally well for the early development of the striated muscle in this region. A comparison of figs. 1 to 21 of the earlier paper with figs. 1 to 17 of the present paper will show this striking similarity. It will be necessary merely to compare the formation
32 CAROLINE MCGILL
of striated muscle with that of smooth muscle already described and to refer the reader to the writer's previous paper for details of the early mj'^ogenesis.
Precisely as in smooth muscle histogenesis, when the formation of striated muscle of the oesophagus begins in the condensed mesenchyme, it is first of all indicated by an elongation of some of the mesenchymal nuclei. For the circular layer of muscle, this begins in the 5 mm. pig embryo. The protoplasm around each nucleus increases in amount and likewise elongates (figs. 16 to 18). Elongation for the formation of the longitudinal layer does not begin in the pig until the embryo reaches a length of 20 mm.
Here, too, as in smooth muscle formation, the statement that muscle arises from undfferentiated mesenchjine is true only for the first few myoblasts formed. In the 15 mm. pig throughout the mesenchyme collagenous fibers appear, as shown by Mallory's stain. Most of the striated muscle arises from this embryonal connective tissue just as does the smooth muscle. Some of the embryonal connective tissue cells in the areas of muscle formation ren^ain undiflferentiated and form the interstitial connective tissue both of smooth and striated muscle.
(6) Increase in the Number of Myoblasts
The increase in the number of myoblasts of striated oesophageal muscle takes place in just the same way as does that of smooth muscle. That is, either by a continuation of the transformation of the embryonal connective tissue cells into myoblasts, or by the mitotic division of myoblasts already formed. Seldom do mitoses occur in the myoblasts after many myofibrillse have appeared.
(c) The Formation of Myofibrillas
Immediately following the elongation of the mesenchymal nuclei, or later, of the embryonal connective tissue nuclei, the myofibrillse arise in the cytoplasm. The myofibrillse, both in the dogfish and in the pig, develop as homogeneous structures without cross-striations. They look exactly like the early fibrilte of smooth muscle. This agrees with the observations of Bardeen ('00), Godlewski ('02) and Eycleshymer ('04).
Two varieties of homogeneous myofibrillae form, the coarse and the fine. The coarse myofibrillae arise in the granular cytoplasmic reticulum.. Many of the coarse protoplasmic granules which are present in large numbers at the time the coarse myofibrillae first appear, seem to be of nuclear origin. As the mesenchymal nuclei in the area of muscle formation multiply by mitosis some of the chromatin appears to be left outside in the cytoplasm (figs. 20, 22, 23). These coarse granules become arranged in clumps to form spindle shaped masses. These spindles are usually close to the nuclei (figs. 18 and 21). The granules in the spindles soon fuse to form homogeneous structures. Neighboring spindles unite to form long, varicose fibrillae (fig. 21).
Mlodowska ('08) has described a similar process in skeletal n\uscle. These coarse, varicose fibrillac extend long distances through the protoplasmic syncytium. In the 15 mm. pig embryo some of them extend over half the circumference of the oesophagus. In time the fibrillae become more nearly uniform in caUber (fig. 17). This type of formation of coarse fibrilla? is found only in the early embryo. All subsequent myofibrillje arise as fine fibrillae which later thicken to form uniform coarse fibrillar. The development of coarse myofibrillae begins in the 9 nun. pig embryo (fig. 16) and in the 30 mm. dogfish embryo (fig. 13).
The formation of fine myofibrillae begins in the 25 to 30 mm. pig embryo. Their development is practically Hke that of the fine fibrillae of smooth muscle. In striated muscle, however, all of them later form coarse fibrillae.
In fig. 25 an interesting stage is seen. Here the first formed coarse fibrillae have become cross-striated. Among them are other coarse fibrillae not jet striated, and also numerous fine myofibrillae just arising. On the periphery of the muscle layer is embryonal connective tissue differentiating into muscle. The myofibrillae here arising are fine in the beginning, not coarse as were the first myofibrillae. These fine myofibrillae gradually thicken and finally also become cross-striated. The first-formed coarse and fine myofibrillae correspond vory closely to the coarse
34 CAROLINE MCGILL
and fine fibrillse found in* developing smooth muscle. In fact, in fig. 17 from a section through the upper oesophagus of a 15 nun. pig embryo, the developing cross-striated muscle has precisely the same appearance as has the developing smooth muscle of the lower oesophagus of the same embryo.
The first evidence of cross-striation in the pig was seen in the 13 nmi. embryo in the muscle of the circular layer of the mid-oesophagus. Few of the homogeneous fibrillae however become cross striated before the embryo reaches a length of 25 mm. Crossstriations were seen in the longitudinal muscle layer of the 27 nun. pig embryo. In the dogfish, cross striations appear in the muscle of the oesophagus in embryos between 50 mm. and 60 mm. in length.
In the development of the striated muscle of the oesophagus, just as in the smooth muscle, the myofibrillae arise everywhere in a syncytium. The syncytium in striated muscle persists until a late stage, when it is par ciallybroken up to form the muscle fibers. This takes place when the sarcolenama differentiates from the interstitial connective tissue. Even after the muscle fibers are formed, the syncytium is in part retained, for each muscle fiber is derived from several cells of the original syncytium.
The nuclei seem to take an active part in the formation of myofibrillae. In their division, as already mentioned, they seem to leave at times much chromatin behind in the cytoplasm, and this chromatic material helps to form the first myofibrillae. Then at the time the fibrillae are forming most rapidly the muscle nuclei are filled with deeply staining chromatin (figs. 17 and 22). In all of these early stages the muscle nuclei stain much more deeply than do the connective tissue nuclei, unless the latter be in mitosis. The fact that in their development the myofibrillae begin to arise near the nuclei, and that the spindle-like enlargements of the varicose fibrillae are usually near the nuclei, is also evidence that the nuclei may take part in fibrillar formation. Now and then in early myogenesis some of the muscle nuclei seem to break down completely and liberate their chromatin into the cytoplasm. This chromatin also may possibly take part in fibrillar formation.
(d) The Interstitial Connective Tissue
The early formation of the interstitial connective tissue is very similar in the striated muscle of the oesophagus to that already described for the smooth muscle, so the details of development are not given here. The connective tissue arises in situ. In skeletal muscle it does not grow in from the outside as has been described by most recent workers, Bardeen ('00), Godlewski ('02), Eycleshymer ('04), Mlodowska ('08), along with many early investigators. There is also no indication in the histogenesis of oesophageal striated muscle of a degeneration of the forming muscle tissue to allow the ingrowth of the connective tissue, as has been found on skeletal muscle by Mayer ('86), Bardeen COO), Godlewski ('02), Eycleshymer ('04), and Mlodowska ('08).
In development, protoplasmic anastomoses between the muscle cells and the connective tissue cells, are everjrwhere demonstrable (figs. 13, 14, 16, 17, 18, 22 and 24). In this protoplasmic syncytium, myofibrillse and connective tissue fibrillse develop side by side. Later, the collagenous fibrillse are crowded out of the muscle protoplasm by the growth of myofibrillse. Numerous figures from material stained in Mallory's anilin blue connective tissue stain, showing the differentiation of the collagenous and myo-fibrilte side by side, are given in the writer's previous paper.
(e) The Relation of Striated to Smooth Muscle
The origin of the oesophageal muscle as traced in the pig and the dogfish embryo seems to confirm Oppel's statement that the smooth muscle is the primitive muscle of the oesophagus. Oppel arrived at his conclusion from the standpoint of comparative anatomy and phylogeny. In the pig and in the dogfish oesophagus, both tissues as we have seen, arise side by side from the conmion mesenchymal syncytium. Until the cross-striations appear in the fibrillse of the striated muscle, both developing tissues look precisely alike. Smooth muscles may retain nearly this primitive structure in the adult. In the lower oesophagus of the pig the adult muscle retains its syncytial structure and has in places practically the same appearance as the embryonal
36 * CAROLINE MCGILL
syncytium in the formation of cross-striated muscle shown in fig. 17. In most places however, more myofibrilte develop in the smooth muscle syncytium, and there is later in the myofibrillse of smooth muscle a tendency to be grouped to form individual spindle-shaped muscle fibers or cells. As far as I have found, all the transitions from smooth to cross-striated muscle in vertebrates oecm* only in the embryo. There is a possibility, however, that even in the adult manmial, intermediate forms between smooth and cross-striated muscle may occur, as Coakley ('92), described in the human oesophagus. At any rate, in development the two tissues are very closely related.
SUMMARY
1. The tissue destined to form the striated muscle of the oesophagus (dogfish) arises from the splanchnic layer of the mesothelium in the region where this epithelium is in contact with the oesophageal endoderm. Apparently there is no connection at any stage of development between this muscle-forming tissue, which is typical mesenchyme, and the cells of the myotome.
2. The mesenchyme in which striated muscle of the oesophagus forms, in both pig and dogfish, is a complete syncytium.
3. In the 4 mm. pig embryo and in the 25 mm. dogfish embryo there is a condensation of the mesenchyme around the endoderm of the oesophagus. In this condensed mesenchyme the muscle arises.
4. The next step in muscle differentiation is an elongation of some of these mesenchymal nuclei accompanied by an increase in the amount of the surrounding cytoplasm. This begins in the oesophagus of the 5 mm. pig embryo and of the 30 mm. dogfish embryo.
5. After the first formation of muscle, the tissue increases in amount in two ways: (1) by addition of new myoblasts from the mesenchyme without, or by differentiation of interstitial embryonal connective tissue cells into myoblasts; and (2) by mitotic division of the myoblasts already formed.
6. As the nuclei elongate in the muscle-forming tissue the myofibrillse arise in the protoplasmic syncytium. The fibrillae form as homogeneous structures, which later become crossstriated. In first formation they are of two types, coarse and fine.
7. The coarse myofibrillae form first and develop by a massing of protoplasmic granules into irregular spindle-shaped structures. The spindles form near the nuclei. Soon the spindles unite end to end to form varicose fibrillae. The granules fuse and the fibrillae become homogeneous and later of uniform caliber. Shortly after this the cross-striations appear. The coarse myofibrillae arise in the 9 nam. pig embryo and in the 30 mm. dogfish embryo.
8. In the older embryos all of the fibrillae form as fine myofibrillae. These increase in size and later may form coarse myofibrillae.
9. Cross-striations were first distinguished in the oesophagus of the 13 mm. pig embryo and of the 50 mm. dogfish embryo. In the pig, however, only a few fibrillae become striated before the embryo reaches a length of 30 mm.
10. The nuclei appear to play an active part in the formation of myofibrillae.
11. The interstitial connective tissue of the oesophageal striated muscle is fonned in situ from embryonal connective tissue cells, which remain undifferentiated* among the muscle cells. There is thus no necessity for ingrowth of connective tissue such as is described in the histogenesis of skeletal muscle.
12. There is at no stage in the development of the striated muscle of the oesophagus a degeneration of muscle cells such as some investigators have found in the histogenesis of skeletal muscle.
13. The muscle tissue remains a complete syncytium until a comparatively lat^ stage, when the interstitial connective tissue grows rapidly in connection with the formation of the definite cross-striated muscle fibers.
14. The smooth and the cross-striated muscle of the oesophagus arise from a common mesenchymal syncytium. In the early stages, up to the time when the cross-striations form, both tissues appear identical in structm-e. The striated muscle of the oesophagus seems to be only a further differentiation of smooth muscle.
38 CAROLINE MCGILL
No transition forms between the two tissues however were found in the adult oesophagus.
LITERATURE LIST
Balfour. Comparative embryology.
1885 Bardben. The development of the musculature of the body wall in the pig, in 1900 eluding its histogenesis and its relation to the myotomes and to the skeletal and nervous apparatus. Johns Hopkins Hospital Reports, Baltimore, vol. 9.
Born. Dissertation. Berlin.
1873 Calbbrla. Studien iiber die Entwicklung der quergestreiften Muskeln, etc. Ar 1876 chiv /. mikr. Anal., Bd. 11.
CoAKLBT. The arrangement of the muscle fibers of the oesophagus. Researches
1892 of the Loomis Laboratory of the University of the city of New
York, vol. 2. Dahlgren and Kepner. Principles of animal histology.
1908 Eycleshtmer. The cytoplasmic and nuclear changes in the striated muscle cell
1904 of Necturus. Amer. Jour, of AncUomy, vol. 3.
Flint. The organogenesis of the oesophagus. Anal. Am., Bd. 30.
1907 GoDLBwsKi. Die Entwickelung des Skelet-und Hertzmuskelgewebes der Siiuge 1902 thiere. Archiv f. mikr. AtuU., Bd. GO.
Hertwig, O. and R. Die Coelomtheorie, etc. Jena.
1881 Hertwig and Mark. Textbook of embryology.
1892 Herzog. Ueber die Entwicklung der Binnenmuskulatur des Auges. Archiv /.
1902 mikr. Anal., Bd. 60
Ingalls. Beschreibung eines menschlichen Embryos von 4.9 mm. Archiv f. mikr,
1907 Anat., Bd. 70.
K5LUKBR. Gnmdriss der Entwickelungsgeschichte des Menschen, etc. Leipzig.
1884 Lewis and Bardben, Development of the limbs, body-wall and back in man,
1901 Amer. Jour, of Anatomy, vol. 1.
Lewis. Development of the arm in man. Amer. Jour, of Anatomy, vol. 1.
1901 Marchesini and Ferrari. Untersuchungen iiber die glatte und die gestreifte
1895 Muskelfaser. Anat. Am., Bd. 11.
Maroo. Neue Untersuchungen iiber die Entwickelung, das Wachstum, die Neu 1862 bildung und den feineren Bau der Muskelfasern. Denkschr. d. K
Akad. d. Wiss. Math-Nalur. KL, Bd. 20. Marshall. On the head cavities and associated nerves of el asmobranchs. Quart.
1882 Jour. Micr. Sci., vol. 21.
Maurer. Entwickelimg des Muskelsystems und der elektrischen Organe. Hert* 1904 wig's Entwickelungslehr der Wirbelthiere, Bd. 3.
Matxr. Die sogenannten Sarcoplasten. Anat. Am., Bd. 9. 1886
McGiLL. The histogenesis of smooth muscle in the alimentary canal and respira.
1907 tory tract of the pig. Internal. MonaUsckr. /. Anat, u, Phys., Bd24.
MiNOT. Human embryology.
1892 Mlodowbka. Zur Histogenesis der Skelettmuskeln. Ext. du. Bull. d. V Acad.
1908 des Set. de Cracome.
Oppbl. Lehrbuch der vergl. mikrsocopischen Anatomie der Wirbelthiere, Bd. 2
1897 Remak. Untersuchungen iiber die Entwickelung der Wirbelthiere. Berlin.
1855 Reutbr. Die Entwickelung der aiisseren Augenmuskulatur beim Schwein. Anat.
1898 Hefte, Bd. 9.
ScHULTZE. Ueber MuskelkOrperchen und das, was man eine Zelle zu nennen habe.
1861 Archiv f. Anal. Physiol., etc.
EXPLANATION OF FIGURES
Abreyiations
ao
aorta
b ec
basement membrane of ectoderm
c
coelom
c mf
coarse myofibrilla
cnu
connective tissue nucleus
cap
capillary
ec
ectoderm
eel
embryonal connective tissue
en
endoderm
et
endothelium
fmf
fine myofibrilla
gmf
granular myofibrilla
h
heart
m
myotome
mc
mesenchyme
mil
mitotic nucleus
m nu
muscle nucleus
ml
mesothelium
mu
muscle
n
notochord
nc
nerve cord
per
cytoplasmic chromatin
-pa
protoplasmic sync3rtium
smf
cross-striated myofibrilla
spmf
spindle of developing myofibrilla.
40 CAROLINE MCGILL
Fig. 1. Cross-section through the body of a 3 mm. dogfish embryo at level of upper oesophagus. There is no mesenchyme formed. The mesothelial cells, mt* show fine protoplasmic processes, a is a loose cell which appears to be a mesenchyme cell just arising from the mesothelium. Zenker's fluid, iron-hflBmatoxylin. B. and L. oc. 10, obj. 16 mm.
Fig. 2. Cross-section through same embryo as in fig. 1, but taken at the level of mid-oesophagus. The myotome, m, is formed. Between the myotome and the coelomic epithelium, mt, is a strand of loose cells resembling mesenchyme. Zenker's fluid iron-luematoxylin. B. and L. oc. 10, obj. 16 mm.
Fig. 3. A section through the lower oesophagus of the same embryo. The connection of the cavity of the myotome with the coelom is shown. Zenker's fluid, iron-h8Bmatoxylin. B. and L. oc. 10, obj. 16 nun.
Fig. 4. A high power drawing of area X in fig. 1 to show the protoplasmic network extending from the mesothelial cells to the surrounding organs. B. and L. oc. 10, Zeiss 2. mm. 1.30 apochrom. obj.
Fig. 5. A high power drawing of region X in fig. 2. The mesothelial cells are more or less united into a syncytium. B. and L. oc. 10, Zeiss 2. mm. 1.30 apochrom. obj. •
Fig. 6. A high power drawing of region X in fig. 3. The mesothelial cells are more or less fused leaving only a partially developed coelom. The mesothelium forms two layers, splanchnic and somatic. Protoplasmic processes are numerous. B. and L. oc. 10, Zeiss 2 mm. 1.30 apochrom. obj.
Fig. 13. Section through the mid-oesophageal mesenchyme of a 30 mm. dogfish embryo; b en, basement membrane of endoderm. Just outside this basement membrane is a thick layer of mesenchymal syncytium made up of stellate cells joined by wide protoplasmic anastomoses. At mu, some of the mesenchymal nuclei are elongating to form muscle nuclei; mf, developing myofibrilla. Sublimateacetic, iron-hsematoxylin. B. and L. oc. 10, Zeiss 2 mm. 1.30 apochrom. obj.
Fig. 7. Cross-section of a dogfish embryo 5.5 mm. in length, at the upper oesophagus. The myotome has grown dorsal to the endodermal tube, en. The rest of the mesoderm is represented by the double layer of mesothelium. The coelom is only a narrow slit between the two layers of mesothelium. Zenker's fluid, ironhsBmatoxylin. B. and L. oc. 10, obj. 16 mm.
Fig. 8. Through mid-oesophagus of a 5.5 nmi. dogfish embryo. The mesoderm s similar to that of the upper oesophagus shown in fig. 7. The blood vessels are growing in, so there is considerable endothelium present, et. B. and L. oc. 10, obj. 16 mm.
Fig. 9. A high power drawing of area X in fig. 8. The drawing extends from the basement membrane of the endoderm, b en, to that of the ectoderm, b ec* The middle germ layer here is represented by the two layers of mesothelium and the endothelium of the blood vessels. No mesenchyme has formed in the region. B. and L. oc. 10, Zeiss 2 mm. 1.30 apochrom. obj.
Fig. 10. A section through mid-oesophagus of a 10 mm. dogfish embryo. The endodermal tube is suspended by a double layer of mesothelium. A is a mesenchyme cell differentiating from the splanchnopleure. Considerable mesenchyme has formed between the somatic mesothelium and the body-wall and also around the myotome. The muscle plate is well removed from the oesophagus, h, heart; c, coelomic cavity; ao, aorta. Zenker's fluid, iron-hsBmatoxylin. B. and L. oc. 10, obj. 16 mm.
Fig. 11. Section through the splanchnic mesothelium and developing mesench3rme of a 10 mm. dogfish embryo near the region shown in fig. 10. At mc are mesenchyme cells which are being formed from the mesothelium. B. and L. oc. 10, Zeiss 2 mm. 1.30 apochrom. obj.
Fig. 12. Cross-section through the mid-oesophagus of a 25 mm. dogfish embryo. The oesophagus is suspended in the coelomic cavity well separated from the other organs. Here an amount of mesenchyme has formed between the mesothelium and the endoderm. The mesenchyme forms a syncytium. The cells are stellate with round or oval nuclei. Sublimate-acetic, iron-hsematoxylin. B. and L. oc. 5, obj . 6 mm.
Fig. 14. Section through the circular muscle layer of the mid-oesophagus of a 60 mm. dogfish. Shows various stages in the differentiation of the myofibrills. Cytoplasm forms a complete syncytium. At the margins, the embryonal connective tissue is differentiating into muscle. Sublimate-acetic, iron-hsematoxylin. B. and L. oc. 10, Zeiss 2 mm. 1.30 apochrom. obj.
Fig. 15. Cross-section through the oesophagus and surrounding tissue of a 7 mm. pig. embryo. Note the condensed mesenchymal syncytium with a few of the nuclei concentrically arranged, h v, blood vessel; ir, trachea; oes, oesophagus. Zenker's fluid, iron-haematoxylin. Zeiss oc. 4, obj. D.
Fio. 16. Section through a portion of the CBSophagus of a 10 mm. pig embryo. This shows the condensation of the cytoplasm and elongation of mesenchymal nuclei to form the circular muscle coat, g mf, coarse cytoplasmic granules arranging in rows, the first indication of the coarse myofibrillse. mil, shows mitosis in the muscle-forming tissue. Zenker's fluid, iron-haematoxylin. Zeiss comp. oc. 8, 2 mm. 1.30 apochrom. obj.
Fig. 18. Small portion of the muscle syncytium from the oesophagus of a 13 mm. pig embryo showing the origin of the coarse myofibrillae from the granular reticulum, gmfy is a mass of coarse chromatic (?) granules; at sp mf, the granules have almost completely fused to form a homogeneous, spindle-shaped mass, a shows a granular strand connecting this spindle with another smaller one. 6 is a myofibrilla arising in part in the protoplasm of an interstitial connective tissue cell. Zenker's fluid, iron-haematoxylin. Zeiss comp. oc. 12, 2 mm. 1.30 apochrom. obj.
Fig. 19. A nucleus from muscle-forming tissue in the oesophagus of a 13 mn^. pig, in prophase of mitosis. It shows the large deeply staining chromosomes. Zeiss comp. oc. 8, 2 mm. 1.30 apochrom. obj.
Fig. 20. A nucleus from the same section as that shown in fig. 19, undergoing mitosis. A large amount of chromatin (p cr) apparently has not entered the spindle but remains outside in the cytoplasm. Zeiss comp. oc. 8, 2 mm. 1.30 apochrom. obj.
Fig. 21. From the same region asfig. 20. This shows the formation of a coarse myofibrilla by the union of spindles near several nuclei. This gives the varicose appearance. Zeiss 6omp. oc. 12, 2 mm. 1.30 apochrom. obj.
Fig. 23. Two mitotic nuclei from the region of muscle formation in the oesophagus of a 13 mm. pig embryo. Nucleus a is in prophase and shows a large amount of chromatin. Nucleus b is in telophase. Many chromatic granules are apparently left in the cytoplasm. Zenker's fluid, iron-hsematoxylin. Zeiss comp. oc. 8, 2 mm, 1.30 apochrom. obj.
Fig. 24. Muscle tissue from the oesophagus of a 13 mm. pig embryo. The coarse myofibrilla at 8 mf is beginning to show cross striations. Zenker's fluid, ironhsematoxylin. Zeiss comp. oc. 8, 2 mm. 1.30 aprochrom. obj.
Fig. 17. Through a portion of the wall of the OBsophagus of a 16 mm. pig embryo near bifurcation of trachea to show area of cross-striated muscle formation. Cytoplasmic syncytium everywhere present. The myofibrillaB show in various stages of development, p cr, chromatic (?) granules free in the protoplasm. The coarse myofibrilla, c m/, ran over one-half way around the oesophagus. Many of the fine fibrils visible in the mesenchyme are collagenous fibrils which can be differentiated with Mallory's anilin blue connective tissue stain. Zenker's fluid, ironhsematoxylin. Zeiss comp. oc. 12, 2 mm. 1.30 apochrom. obj.
Fig. 22. The muscle syncytium from the mid-oesophagus of a 16 mm. pig embryo. The large amount of chromatin (?) in the protoplasmic syncytium is noticeable, -per. The muscle nuclei stain very intensely. Zenker's fluid, iron-hsematoxylin. B. and L. oc. 10, Zeiss 2 mm. 1.30 apochrom. obj.
Fig. 26. A section through the inner part of the circular muscle layer of a 27 mm. pig oesophagus. This section shows a number of stages in the formation of myofibrillae. The oldest fibrillae are cross-striated, s mf, c m/ is a coarse myofibrilla only in part striated. / m/ are fine fibrillse just arising. In the adjacent embryonal connective tissue numerous cells are elongating to form muscle. With Mallory's anilin blue connective tissue stain, these cells are found to contain both myofibrillse and collagenous fibrils. Cap is a capillary. Zeiss comp. oc. 8, 2 mm. 1.30 apochrom. obj.
BOOK REVIEW
A Text-Book of Anatomy. Edited by D. J. Cunningham, F.R.S. Third Edition, 1909. New York: William Wood and Company.
The revision of the third edition of Cunningham's Text-Book of Anatomy was the last labor of its distinguished editor. The style and plan of the third edition remain the same as in previous editions. The sections on Osteology and Myology have been largely rewritten and the descriptive matter altered to conform to the BNA terminology and much has been gained thereby in clearness of style and conciseness of expression. It is to be hoped that the remaining sections of the book will undergo revision in the near future and the use of the BNA nomenclature consistently followed.
The number of pages in the section on Osteology remain the same as in the second edition, with thirty-four additional illustrations. In the description of the bones of the extremities new drawings are introduced, delineating in color the origin and insertion of the muscles. The bones entering into the construction of the skull as a whole, and in different planes of section viewed from various aspects, have been differentiated in this manner. Color likewise has been used to distinguish the articular surfaces of the bones of the hand and foot. There are several new radiographs of the foetal hand and foot.
Appended to the section on Osteology are six short but comprehensive accounts of: (A) Architecture of the bones of the skeleton; (B) Variations of the skeleton; (C) Serial homology of the vertebrse; (D) Measurements and indices employed in physical anthropology; (E) Development of the chondrocranium and morphology of the skull; (F) Morphology of the limbs.
The number of pages in the section on Myology are slightly increased and the new drawings are excellently executed. Many of these in their handling and representation show the influence of Spalteholz's Atlas. Of the drawings of the sole of the foot, three are taken from the left side and one from the right. Further, figures 294 and 301 are placed on the page with the digital extremities away from the observer, while figures 303 and 304 have a reversed position. The same discrepancy exists in the representation of the palmar aspect of the hand. The figures do not show clearly the manner of insertion of the flexor tendons and their disposition after entering the flexor sheaths.
A "Glossary of Anatomical Terminology" is prefaced to the introduction, giving a short historical account of the Basle Nomina Anatomica.
Henry W. Stiles.
PRELIMINARY PROGRAMME
Of the II. International Anatomical Congress, Brussels, August 7-11, 1910.
SUNDAY, august 7
4:30 p.m. Session of the committee, consisting of the presidents and secretaries of the five united societies, and also the president and secretary of the local committee, to be held in the Anatomical Laboratory, Park Leopold: entrances rue Belliard and rue du Walbeck.
8 :30 p.m. Welcome in a place to be announced.
MONDAY, 8th; THURSDAY, 11th.
Mommgs, from 9 to 1. Sessions.
Afternoons, from 3 to 6. Demonstrations.
The scientific sessions will take place in the auditorium of the Physical Institute of the University, 14 rue des Sols.
The demonstrations will be held in the Physical Institute, Park Leopold.
The local committee consists of Messrs. Rommelaere, president of the Administrative Council of the University; Paul Ererra, Rector of the University, and Raoul Warocque, the founder of the Anatomical Institute, as honorary president. Professor Brachet as president, and Professor Joris as vice president.
Committee on Lodgings : Dr. Brunin, Chef des travaux (Anatomie) .
Information concerning anatomy, comparative anatomy, and embryology may be obtained from Professor Brachet, rue Sneessens 18; for histology. Professor Joris, rue de President 73.
A banquet is proposed for Wednesday, August 10.
SYMPOSIUM ON COMPARATIVE NEUROLOGY^
1. THE PHYLOGENETIC ORIGIN OF THE NERVOUS
SYSTEM
G. H. PARKER
Harvard University
The highly differentiated nervous system, such as is f oimd in the vertebrates and other higher metazoans, is described as composed for the most part of many inter-related reflex arcs. Each of these arcs involves at least three parts: a sense organ or receptor which receives the external stimulus and originates the nervous impulse; a central nervous organ or adjustor in which the impulse may be variously modified and directed; and a muscle, gland, or other effector by which the animal responds to the external stimulus. Nerve fibers connect, of course, the receptor with the central apparatus and the latter with the effector. At least two classes of neurones are concerned in this mechanism, one afferent or sensory and the other efferent and usually motor. The sensory neurone is modified at its peripheral end to form the receptor and its nerve fiber extends as a rule to the central organ in which it ramifies; its cell-body may occupy a peripheral position even forming an essential part of a sense organ as in many invertebrates and in the olfactory organ of vertebrates, or it may be nearly central in location as in the spinal ganglia of the vertebrates. The motor neurone has its cell-body within the central organ and its fiber as an efferent fiber extends to a muscle where it terminates. Besides these two classes of neurones, afferent and efferent, the central organs usually contain a vast congregation of correlation neurones which in one way or another intervene between those already mentioned.
^Presented at the twenty-fifth session of the American Association of Anatomists, Boston, December, 1909.
52 G. H. PARKER
Such a nervous system as the one just described is found in the vertebrates, moUusks, anthropods, worms, and other higher metazoans, but is only feebly represented, if in fact it can be said to be represented at all, in the echinoderms, ctenophores, and coelenterates. The part that is least developed in these lower animals is the central organ, and, though this part cannot always be said to be absolutely unrepresented, it is so deficient, especially in the coelenterates, as to have led to the designation of their nervous apparatus as diffuse rather than centralized. The so-called diffuse nervous system of these animals is the simplest nervous system with which we are acquainted, for, notwithstanding repeated efforts, no true nervous structure has ever been demonstrated in those metazoans which, like the sponges, are more primitive than the coelenterates. If, therefore, the beginnings of the nervous system are to be sought for, attention must be directed to the coelenterates.
The coelenterate body is composed chiefly of two specialized epithelial layers, ectoderm and entoderm, each of which contains both nervous and muscular elements. The nervous elements are epethelial sense-cells whose receptive ends are at the periphery of the layer in which they are contained and whose nervous ends form a system of extremely fine interlacing branches many of which are probably directly* connected with the deep-seated muscle-cells. The fine branches from many neighboring sense-cells establish what is probably a true nervous net by which transmission is accomplished not only to the subjacent muscle-cells but to those some distance away. Here and there this net contains conspicuous, multipolar cells which contribute fibrils to it and which for this reason are believed to be nervous. It is with the origin of this relatively simple neuromuscular mechanism that we are concerned.
In 1872 Kleinenberg announced the discovery in the fresh-water hydra of what he designated as the neuromuscular cell. The peripheral end of this cell was situated on the exposed surface of the epithelium of which it was a part and was believed to act as a nervous receptor; the deep end was drawn out into a muscular process and served as an effector to which transmission was supposed to be accomplished through the body of the cell. Each such cell was
THE PHYLOGENETIC ORIGIN OF THE NERVOUS SYSTEM 53
regarded as a complete and independent neuromuscular mechanism, and the movements of an animal provided with these cells were believed to depend upon the simultaneous stimulation of many such elements. It was Kleinenberg's opinion that these neuromuscular cells divided and thus gave rise to the nerve-cells and muscle-cells of the higher animals. In fact he declared that the nervous and muscular systems of these animals were thus to be traced back to the single type of cell, the neuromuscular cell, which morphologically and physiologically represented the beginnings of both.
Some years later, in 1878, the Hertwigs published an account of the minute structure of the coelenterate nervous system and showed thatKleinenberg's so-called neuromuscular cells were probably merely muscle-cells in process of differentiation. They consequently proposed for these cells the more appropriate name of epithelio-muscle cell. They also claimed that in the evolution of the neuromuscular mechanism in coelenterates the three types of cells that they had identified, the sense-cells, ganglion-cells, and muscle-cells, were simultaneously differentiated from ordinary epithelial cells. Thus these three elements, though regarded as derived from a common layer, were, according to the Hertwigs, not the descendents of any single type of cell such as the neuromuscular cell.
Although Kleinenberg's theory and the theory of the Hertwigs differ in certain important details, they agree in declaring for the simultaneous and interrelated evolution of nerve and muscle. As contrasted with this view is the hypothesis that was first advocated by Claus and later by Chun that the two types of tissue arose independently and became secondarily united. In 1880 Chun called attention to the fact that in vertebrates the motor nerve-fibers grow out of the medullary tube and become connected with the muscles secondarily and he regarded this as evidence that nerve and muscle had arisen in phylogeny independently and had become secondarily united. But the majority of investigators have sided with the opinion expressed by Samassa (1892) that a nervous system purely receptive in function and without effectors of any kind is practically inconceivable. Hence the hypothesis of Claus and Chun has been generally regarded as untenable.
54 G. H. PARKER
The current opinion among investigators as to the evolution of the nervous system of primitive metazoans remains essentially that of the Hertwigs, namely that nerve and muscle have been differentiated simultaneously and in close physiological interrelation but from cells which were separate members of an epithelium. To this view I wish to oflfer certain opposing facts obtained from a study of sponges. It has already been stated that no nervous structures have been definitely identified in the sponge, nor is there, so far as I am aware, any physiological reason to suppose that such exist. Nevertheless these animals are capable of some movements and their movements are so related to changes in the environment as to be classed as normal reactions. Under this head may be placed the closing and opening of the oscula and of the pores, and certain general movements of the whole body of the sponge. The closing of the oscula and of the pores is carried out by sphincters composed of spindle-shaped cells which in many respects resemble smooth muscle-fibers. These cells are unprovided with nerves and are brought into action, so far as I have been able to ascertain, by direct stimulation. I therefore believe them to be independent effectors and that the sponge is an example of an animal that possesses muscle but no nerve. If, as seems probable, muscle without nerve exists in these primitive metazoans, it follows that we are no longer justified in concluding that nerve and muscle have differentiated simultaneously, but it must be admitted that muscle is phylogenetically the older. I therefore believe that the beginning of the neuromuscular mechanism is to be found in the appearance of independent effectors such as muscles and that sponges probably represent this initial stage in the evolution of the mechanism concerned. Some physiologists may be inclined to question the actual occurrence of normally independent effectors, but the heart of Salpa, and that of the chick embryo before it becomes invaded by nervous tissue are examples of this kind, and it is now well known that though the sphincter pupillae of the vertebrate eye is under the control of nerves, it also responds directly to light. These instances seem to me a sufficient warrant for a belief in the existence of independent effectors.
Although the sphincters of sponges are effectors without nerves,
THE PHYLOGENETIC ORIGIN OF THE NERVOUS SYSTEM 65
they are good examples of the kmd of centers around which nervous tissue probably first arose. This development can be conceived to have occurred in the epithelial cells in the immediate proximity to such a center, in that these cells gradually assumed a special receptive function whereby they could stimulate the adjacent muscle more efficiently than it could be stimulated directly and thus an ordinary epithelial cell would gradually be converted into a receptive or sense-cell. From this standpoint the original function of the sense-cell was merely that of a delicate trigger by which the muscle would be more certainly and efficiently brought into action than through its own receptive capacity and many sense-cells in the lower metazoans probably still retain this as their sole function. Such cells occur abundantly in the coelenterates and hence I regard the sense-cell as the first type of nervous tissue to be differentiated. Since sense-cells and muscle-cells make up the chief part of the neuromuscular apparatus of coelenterates, I have designated this apparatus as a receptor-effector system.
But coelenterates usually show more than a simple receptoreffector system, for the fine branches from their sense-cells not only reach their muscle-cells but also anastomose with one another and form a nervous net. Such a net is the first step toward the formation of a central nervous organ or adjustor and its origin in relation to the sense-cells and the muscle-cells is probably so strictly local that it practically realizes Hensen'sview as to the histogenetic relations of nerve and muscle, namely that these elements are not developed separately and brought into connection secondarily, but that their connections are original and give evidence of the incompleteness of cell division in the course of ontogeny. Such nets serve as more or less diffuse transmitters and are supplemented by the fibrils from certain contained cells, the so-called ganglion cells, which have migrated into the net and which probably mark the first step in the growth of those accumulations of cell-bodies that characterize the central nervous organs of the higher animals.
If this view as to the mode of origin of the central nervous organs is correct, it follows that these organs myst be controlled in their incipiency by the sense organs. In such coelenterates as sea anemones where the sensory specialization is slight, there is scarcely
56 G. H. PARKER
any evidence of centralization in the nervous net, but in jelly fishes where the sense organs are specialized and in groups, each group has associated with it a region of special development, an incipient central organ in the nervous net. In bilateral animals such as the annelids and the crustaceans, the chief portion of the central nervous system, the so-called brain, is also associated with a group of sense organs and these organs, essential to the anterior end of any animal that moves forward, determine, in my opinion, the position of the brain rather than the reverse. Even in the vertebrates where the brain arises to a dignity not attained by any other nervous organ, its anterior position has been determined, I believe, by the location of the sense organs rather than that the sense organs are at the anterior end because the brain is there.
But although the central nervous organs have probably developed from a nervous net under the influence of the sense organs, they have taken in their later evolution a course more or less their own. Even the nervous net, which, in my opinion, unquestionably exists in the lower metazoans, has been denied in the central nervous organs of the higher animals. But it is not impossible that in these more specialized forms a nervous net may have a local existence. Evidence that nervous nets do not exist in certain parts of the vertebrate nervous system does not prove that they may not occur in other parts of this system. In the myenteric plexus of the vertebrate intestine the relations of nerve and muscle are such as to recall most strikingly the conditions already portrayed in the nervous net and muscles of the coelenterates and it is possible that nervous transmission in these animals follows the same rules that it does in the vertebrate intestine. In the vertebrate retina, too, the histological evidence is strongly in favor of a nervous net and the fact that the cells of the retina are members of the same epithelial layer and may therefore always have retained primary connections, suggests a fundamental similarity with the conditions in the coelenterates. Thus there are localities in the nervous systems of even the most highly differentiated animals where these most primitive of central structures, the nervous nets, very probably occur. But to claim on the basis of these instances that the whole central nervous system of the vertebrate is constructed on the plan of a nervous net would be going far beyond the facts.
It is well established that in the histogenesis of the central nervous organs of the higher animals, many cells that are ultimately in most intimate physiological relations, are in their early stages of development far asunder and that they attain to their final close relations by throwing out processes that grow toward one another. It is probable that these processes never really unite into continuous transmitting tracts but retain at least a certain physiological separateness, for in such parts of the central organ where these relations occur, transmission is not diffuse, as in the nervous net, but is limited to a single directon. Central nervous systems having these peculiarities have been called synaptic because the contact points between their cells, the synapses, are believed to be the parts that in some way govern the direction of transmission. This synaptic system has in the higher animals replaced to a considerable extent the more primitive nervous net and though this nervous net may still exist in some parts of the central nervous apparatus of such animals as the vertebrates, it is not the structure that gives to these organs their distinguishing characteristic. In these organs the fully differentiated nerve-cell or neurone with its synaptic connections is the characteristic structural unit of the system. Combinations of such imits make up large parts of the central nervous organs of the higher animals and possess apparently physiological possibilities of a vastly higher order than can be found in the more primitive nervous nets; they have thus afforded the structural basis for the nervous activities of all the higher animals. Although the nervous net with its capacity for diffuse transmission was the structure in which the central nervous system took its origin, I nevertheless believe that this system early underwent fundamental changes whereby synaptic neurones with transmission in restricted directions replaced in large part the more primitive system of diffuse nervous nets.
The facts briefly stated in the preceding paragraphs justify the conclusion, I believe, that muscular tissue and nervous tissue have not arisen at the same time phylogenetically, but that muscle in the form of independent effectors preceded nerve in its develop
58 G. H. PARKER
ment and that nervous tissue differentiated in close proximity to muscle tissue as groups of sense-cells or receptors. Still later central nervous organs developed between the receptors and the effectors, first as clusters of nerve or ganglion cells which added to the nervous nets and later as aggregates of synaptic neurones from which were formed the more complex nervous organs of the higher anmals. Thus the three parts of the dijBferentiated neuromuscular system of the higher animals have, in my opinion, developed in sequence: first, the muscle or effector; next, the senseorgan or receptor; and last, the central organ or adjustor.
2. THE RELATIONS OF THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS IN PHYLOGENY
C. JUDSON HERRICK
University of Chicago WITH TWO TEXT FIGURES
The fundamental factors in the diflferentiation of nervous and non-nervous tissues have been clelarly presented by Dr. Parker, whose researches have the great and rare merit of combining both anatomical and physiological view-points and methods.
I commented yesterday* upon the striking parallelism between the series of animals when arranged according to structure by the comparative anatomists and the series when arranged according to functional type by students of animal behavior, and I pointed out that the ventral segmented ladder type of central nervous system, as seen in annelid worms and arthropods, naturally by virtue of its structure expresses itself in rigidly predetermined or stereotyped instinctive behavior, while the dorsal tubular and imperfectly segmented nervous system of vertebrates is structurally adapted to serve both reflexes and instincts as in arthropods and also the more plastic individual reactions of the intelligent type. The pre-eminence of vertebrates in the ability to perform individually acquired intelligent acts not predetermined in the hereditary nervous pattern is due primarily, I maintain, to the mechanical advantages of the tubular nervous system as compared with the ladder type of nervous system in the elaboration of correlation tissue, and I wish now to illustrate this thesis somewhat more fully from the anatomical side.
Let us take as our point of departure a very simple metazoan
' The Evolution of Intelligence and its Organs. Address of the vice-president and chairman of Section F, Zodlogy, of the American Associatior for the Advancement of Science. Science, N. S., vol. 31, No. 784, pp. 7-18, Jan., 1910.
60 C. JUDSON HERRICK
body with a differentiated head end, bilateral symmetry and a diffuse or very imperfectly centralized nervous system, such an animal, say as a tiu'bellarian worm (Fig. 1), which habitually creeps upon the ground. Within the outer epitheUum is a layer of locomotor musculature (M) and a central digestive tract (G) and between these the other organs of vegetative life. Outside impressions are received chiefly by contact stimuli; and the diffuse nervous system is concerned for the most part with these stimuli and with internal or visceral reactions. The dorsal epithelium (SEN) alone is exposed to any considerable number of stimuli from distant objects, such as Ught and heat rays, currents and vibratory disturbances in the surrounding medium, emanations of odorous particles, etc. This animal can respond to a very small number of such stimuli. If such a species continues to crawl upon
SCN.
Fig. 1
or within the mud, after the manner of the worm-like ancestors of the arthropods, the contact receptors, especially those of the ventral and lateral surfaces, will in the course of evolution become more highly developed and the diffuse nervous system is naturally concentrated into a ventral central nervous system contiguous to these receptors. This vermiform locomotion and the associated transverse segmentation have in fact so firmly fixed the ventral ladder tjrpe of nervous system in the articulate phylum that even the free swinaming crustaceans and the insects depart but little from it.
If, however, the hypothetical ancestral species with a diffuse nervous system assumes from the start a free swimming habit, this will tend to promote the differentiation of the dorsal distance receptors rather than the ventral contact receptors. That is, the
THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS 61
stimulation complex which reaches this free swimming body will contain a relatively smaller proportion of elements aflfecting the ventral and lateral body surfaces by contact and a larger proportion of elements emanating from distant objects and reaching the dorsal and oral surfaces.
Not only has such a differentiation of the dorsal epithelium undoubtedly taken place in ancestral vertebrates, but the primary correlation centers for these receptors have also been derived from the same source, and ultimately the correlation centers for the greater part of the contact and visceral reactions came to be incorporated with them, only the peripheral sympathetic system retaining the primary diffuse formation.
Sherrington has shown^ that the mammahan cerebral cortex has been elaborated largely to serve the distance receptors; I think that we may carry the idea further back and say that the entire vertebrate central nervous system was from its earliest inception differentiated away from the anneUd and arthropod tjrpe under the same influence.
A difference in habitual reaction to the common environmental forces on the part of a primitive animal with a diffuse and undifferentiated nervous system may, therefore, be said to have set the direction of two divergent lines of adaptation, one culminating in insects with (predominantly) instinctive action systems, the other culminating in primates characterized by individually adaptive and intelligent actions. The ultimate explanation for this divergence goes back, as in the case of all other evolutionary movements, to differences in the animaUs reactions to the environment. Once the structural pattern has been thus laid down and fixed in the hereditary machinery, perhaps by natural selection, the future course of evolution is in some measure predetermined by the structural possibiUties of the organs so differentiated. Thus, the ventral ladder type of nervous system favors the differentiation of an instinctive type of behavior based fundamentally on segmental reflexes, while the dorsal tubular type is better adapted for the development of longitudinally arranged correlation tissue which
The Tntegrative Function of the Nervous System. New York, 1906
62 C. JUDSON HERRICK
facilitates total rather than segmental responses and a higher degree of integration of the whole system. Here I think we have clearly the machinery of a certain kind of determinate evolution which contains no elements of mysticism but rests on an intelligible basis of inherited tjrpe of nervous organization and action system.
Herbert Spencer's definition of life is biologically sound in that he makes the measure of correlation of internal with external forces the criterion of life. The lowly organism touches the environment at few points, receives but little from it and gives but little back. With the increase in the range of this effective contact with outer forces, the mechanism of internal regulation necessar* ily becomes more complex. Thus we have from the beginning of dififerentiation the somatic or exteroceptive activities set over against the visceral or interoceptive.
This finds its anatomical expression in two fundamentally distinct types of reflex arcs: (1) the somatic system, comprising the peripheral or exteroceptive sense organs, somatic sensory nerves and cerebral centers and somatic motor centers and peripheral nerves ending in the skeletal muscles, the whole system serving those reactions which the animal makes in response to external stimuli. (2) The visceral system, comprising the sense organs of the viscera, termed interoceptors by Sherrington, the visceral sensory nerves and centers and the visceral efferent centers and peripheral nerves, terminating in visceral muscles, glands, etc. The coordinating centers of the visceral system are partly peripheral in the sympathetic ganglia and partly in the central nervous system; those of the somatic system are wholly central.
In the central nervous system, then, we find evidences more or less clearly preserved of four fundamental longitudinal colmnns on each side of the body. These are so arranged that as one passes from the dorsal toward the ventral side of the neural tube in cross section he meets first the somatic sensory centers, then the visceral sensory, the visceral motor and the somatic motor. The relations of the four primary longitudinal columns of the central nervous system to the dorsal ectoderm will next be considered.
In all vertebrate embryos we find the dorsal nervous tissue at
THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS
63
the appropriate stage in the form shown m Fig. 2, the mid-dorsal epithelium being in process of invagination to form the neural tube. The figure is pinrely schematic and includes some features which are clearly differentiated only in later developmental stages. The somatic sensory surface (exteroceptors of Sherrington) includes both specialiaed sensilte (SEN) and general sensory endings widely distributed in and imder the epidermis. At the Up of the neural groove is the neural crest tissue (N.C), from which the spinal ganglion cells will arise. These receptive cells sometimes, however, remain in the outer epithelium, either permanently, as in the olfactory organ, or temporarily, as in the gan
SEN.
Rg. 2
glionic elements which are added to the cranial nerve ganglia from the embryonic cutaneous placodes. In other cases they are incorporated in the neural tube, as in the giant cells of. the spinal cord of some fishes and the retina.
In the walls of the neural tube the dorsal part becomes the primary sensory centers, and separated from it by a very constant longitudinal groove, the sulcus limitans (S.L.) the ventral part becomes the primary motor centers. These are further subdivided, the somatic sensory centers (exteroceptors and proprioceptors of Sherrington) lying dorsally close to the neural crest and outer skin, the somatic motor far ventrally close to the myotomes and
64 C. JUDSON HERRICK
the visceral sensory and motor between. These four primary functional columns can be more or less clearly recognized on each side of the neural tube in all vertebrates. This arrangement, while very different from that of arthropods, is per se no better adapted for higher psychic manifestations. But in later embryonic stages, to these primary centers there is added* the correlation tissue of the reticular formation and the suprasegmental centers; and we have the key to the greater potentiality of the vertebrate tjrpe in the favorable form of the tubular nervous system, as contrasted with the ladder type, for the elaboration of this tissue.
The organs of somatic response in vertebrates are themselves so very complex as to require a special coordinating machinery of their own, such as muscle spindles, sensory endings of tendons, joints, etc. These, with their cerebral centers and return pathways, are termed by Sherrington the proprioceptive reflex apparatus. It is genetically and anatomically subsidiary to the exteroceptive system. Besides the sense organs within the somatic muscles, etc., mentioned above, this system includes the organs of the labyrinth of the internal ear and the associated cerebral centers of equilibration and muscular coordination. The cerebellum has been developed from the somatic sensory column of the medulla oblongata as the chief central coordinating apparatus of the proprioceptive system. The somatic system of reflex arcs is, accordingly, divided into exteroceptive and proprioceptive systems, whose receptors and cerebral centers are distinct, but whose efferent pathways are the same — to the somatic muscles in both cases.
The exteroceptors are further subdivided into contact receptors (organs of touch, etc.), and distance receptors (such as the eye and ear) the former being stimulated by objects at the body surface, the latter by forces emanating from distant objects. Evidently the tjrpe of reaction must necessarily be very different in the two cases.
The anatomical structure of the vertebrate central nervous system has been molded under the influence of two factors which have often been antagonistic. The first of these is the primary bodily metamerism, in accordance with which each segmental
At the Baltimore Meeting of the Anatomists in 1908, several anatomists interested in the study of human embryology decided that it is desirable to publish a list of the human embryos found in our various laboratories, in the Anatomical Record. It is believed that this list will be not only of great value to those who are conducting studies in the anatomy of the human embryo but also will encourage others to collect embryos and make them available for scientific research.
The list now prepared includes those embryos in the principal collections, but it is desirable to make it as complete as possible. Those who have specimens which they wish to include in this catalogue are requested to send the data, as indicated below, to Dr. F. P. Mall, Johns Hopkins University, Baltimore, within the next few weeks.
List of Human Embryos in the Collection of
No. of Embryo
No. of Slides in Series
Crown Rump Length
in millmeters
Fresh
Formalin
Alcohol
Clearing fluid
On slide
Remarks
( T. Transvenie
Direction of Section ^ s. sagituu
[ F. FroDtal
Thickness of Sections in microns Stains
r E. Excellent
Condition of tissues | ^ ^^
I p. Poor
THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS 65
nerve tends to repeat exactly the same arrangement of components. This is far more evident in the lower vertebrates than in the higher, though it is never so important a factor as in the annelid worms and most articulata. This factor is more and more completely obscm'cd as we ascend the vertebrate series by the second factor, viz., the longitudinal integration and correlation of the several functional systems which we have enumerated above. The more highly developed functional systems tend to be structurally more perfectly unified and concentrated, and this disturbs both the metameric and the longitudinal patterns. Examples of this sort of disturbance are found in the tendency of all of the cutaneous nerves of the head to enter by the trigeminus and of the vagus to absorb the visceral components. In the rostral end of the brain the development of the massive suprasegmental correlation centers disturbs the primitive relations still more. But the primary pattern as we have outlined it is clearly evident in the structure of the medulla oblongata (either adult or embryonic) and its nerves in all vertebrates, and the comparative morphology of this part of the nervous system may be regarded as definitely established in its main features. The history of the steps by which this correlation has been effected would be an interesting contribution to scientific method.
After the formulation of Bell's law of the sensory character of the dorsal spinal roots and the motor character of the ventral roots, morphologists were long absorbed in the vain attempt to reduce the cerebral nerves to a similar simple segmental scheme. Even after Gaskell and His had laid the foundation for a true morphology of the medulla oblongata and its nerves, the deceptive simplicity of the older metameric schemata still domhiated the field and misled some of our ablest anatomists and embryologists.
As anatomists we have been slow to recognize the importance to our work of certain facts which have long been physiologically obvious. It was not until members of our own number, working with anatomical methods, brought out the structural pattern of the nervous system in some of the lower vertebrates where it presents almost diagranmiatic simplicity, that we have directed our attention to them.
66 C. JUDSON HERRICK
For four hundred years the cranial nerves had been dissected and for fifty years their central courses had been studied microscopically before any one succeeded in effecting a precise correlation of the peripheral with the central courses by following the nerve roots accurately through the ganghonic plexuses, and thus making an anatomical demonstration of the composition of the reflex arcs known physiologically to be there represented.
Acting under the stimulus of a suggestion made by Professor H. F. Osbom in 1888, a small group of American neurologists has patiently unravelled the tangled threads of the cranial ganglionic complexes in representative vertebrates, and now we are able to formulate a structinral paradigm or t jrpe form of cerebral nerve components for the vertebrates as a class. The completion of the picture by the addition of f inrther anatomical details, especially as to the corresponding central relations, by embryological studies and by physiological experimentation is rapidly progressing. This doctrine of nerve components, though first formulated in anatomical terms, is essentially a physiological conception, defining the peripheral and central pathways of the great fundamental types of reflexes, as I have endeavored to show by placing the emphasis on the physiological side and by the use, in this discussion, so far as possible, of the luminous terminology of Sherrington.
That the fimdamental pattern of the vertebrate nervous system, as here laid down in terms of functional systems, is scientifically true is shown by the essential harmony of the data developed, for the most part entirely independently, in the fields of comparative anatomy, physiology and embryology. Conversely the most recent and perhaps the most striking illustration of the clarifying influence of these physiological units upon vexed morphological questions is given by the work of Landacre to be reported in this symposium.
The whole ectoderm of the vertebrate embryo, particularly on the dorsal side, must be regarded as potentially nervous. Part of this tissue is incorporated into the neural tube, a part is used to form the neural crest and peripheral neurones and a part develops sensory functions in situ peripherally. The relations of the peripheral receptive cells to the parent ectoderm are various. Prim
THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS 67
itively these receptors were in the epidermis and some retain this position throughout the whole course of the phylogeny, as in the case of certain elements in the skin of annelid worms and of Amphioxus and in the vertebrate olfactory organ.
The general cutaneous innervation in lower forms is responsive to a considerable variety of stimuli. Even the human skin has several very different sensation qualities whose physiological analysis has proven very difficult, and it is still uncertain whether all of these qualities are served by specifically different nerve fibers or whether the analysis is in part central. The whole skin is very sensitive to chemical stimuli in fishes and in man it has been shown that general sensory nerves, not belonging to the gustatory system, are sensitive to certain chemical stimuli wherever they distribute to moist surfaces, as in the mouth cavity, though special end-organs, nerve components and central stations are differentiated for the more highly specialized chemical senses, taste and smell.
Parker has shown that the general body surface of lower vertebrates is also sensitive to light. But the great physiological importance of distance receptors of this type has led to a concentration of this function in special areas of ectoderm, the optic pits, which were involved in the invagination of the neural tube and finally again evaginated as the optic cups in order to bring the retinal surfaces into a peripheral position more favorable for receiving the light rays. That the retina is a modified somatic sensory receptor is confirmed by Johnston's demonstration of the close anatomical relationship in lower vertebrates of its most primitive cerebral center, the tectum opticum, with the general cutaneous centers. An interesting side light is also shed upon this question by Whitman's demonstration in 1892 (Festschrift f. Leuckhart) that in certain leeches sensillse appear on each segment which in the caudal part of the body apparently function as organs of touch, but as we pass toward the head in successive segments, they become progressively modified in the direction of photoreceptors until in the head segments they are well formed eyes. Though this is probably a case of independent parallel differentiation, and is not ancestral to the vertebrate visual organs, it assists in the interpretation of the latter.
68 C. JUD80N HERRICK
The ganglia of unspecialized sensory components of the peripheral nerves m general, both visceral and somatic, are derived from the neural crests, i. e., from masses of ectoderm at the lateral borders of the neural tube at the line of its separation from the general ectoderm. That this neinral crest tissue is intermediate in type between the general ectoderm and the neural tube is shown by the fact already mentioned, that the ganglion cells of peripheral general cutaneous nerves are sometimes enclosed within the neural tube (the so-called giant cells of the spinal cord of some fishes) instead of lying in the usual position laterally of the spinal cord.
Evidence is constantly accumulating that some if not all of the special sensory components have been derived from the unspecialized visceral and somatic sensory components. The history of the evolution of the lateral line and auditory systems from the unspecialized somatic sensory systems may be regarded as demonstrated from the fields of comparative anatomy, comparative physiologj'^ and comparative embryology. The history of the central diflferentiation of the lateral Une lobe and tuberculum acusticum from the somatic sensory colunm has been clearly demonstrated anatomically by Johnston; that the lateral line and auditory functions are closely related to the general tactile sense has been shown physiologically by Parker; and Landacre is able to illustrate in the embryological history of fishes an interesting relation between the neural crest and the dorso-lateral series of placodes in the origin of the lateralis and acoustic ganglia.
A similar history is presented in the visceral sensory system, where the ganglia of the unspecialized visceral nerves come from the neural crest, while those of the specialized gustatory component come from a special system of cutaneous placodes.
The olfactory nerve probably belongs to the last tjrpe, with this difference, that its peripheral neurones retain their positions in the placode instead of migrating inward to form a ganglion. There are, however, some elements which migrate from the olfactory placode to form a deep ganglion on the olfactory nerve, whose morphology is very obscure. Some of these migrating elements have been shown by Brookover in Amia to form sheath
THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS 69
nuclei of the olfactory fibers, others differentiate into the neurones of the ganglion of the nervus tenninalis. The character of the latter nerve and ganglion demands further investigation.
Thus we find that each functional system of nerves has its peculiar type of development, peripheral end-organs, nerve components, ganglia and central connections, and for that the reflex arcs established among these fimctional systems constitute the most valuable imits of nervous structmre and function. Segmental and other gross subdivisions, which have the sanctions of long use and practical convenience, will of course continue to serve a useful purpose, but the fundamentally valuable data of neurology will more and more tend to be cast in the molds of these functional systems. This is true because in animal evolution the controlling fact has been the adjustment of the body to various environmental influences and the nervous system has been the medium of this adjustment.
===3. The Origin Of The Sensory Components Of The Cranial Ganglia===
Francis L. Landacre From Ohio State University, Columbue, Ohio
WITH THREE FIGURES
Professor Herrick has set before us clearly the principal conclusions derived from the attempt to analyze from a functional standpoint the cranial ancj spinal nerves, chiefly among the Ichthyopsida. The writer will confine himself to the inquiry as to what support these conclusions find in the development in a favorable tjrpe such as Ameiurus, laying emphasis largely upon the mode of origin and the morphological relations of the cranial ganglia, exclusive of the sympathetic ganglia. The ganglia in the vertebrates are the source of the central and peripheral fibers which have been grouped into the various component systems, and are in a very literal sense the foundation of these systems. Their mode of origin must affect vitally oiur conception of the theory of nerve components. The cat-fishes were chosen as a type, partly because the nerve components of the adult are known through Dr. Herrick's work, and partly because the character of the gustatory system is such that it seemed to be a favorable form in which to differentiate between the special visceral and general visceral systems of ganglia.
In contrast with the favorable conditions offered by the embryo, the cranial nerves of the adult cat-fish are much more diflScult to analyze than those of such a form as Menidia, but by going back to a stage between eighty and ninety hours after fertilization, we find the ganglia in such a simple condition, with so little fusion of the various ganglionic components, that their analysis becomes comparatively easy. At this stage (as shown in fig. 1) we find
72
F. L. LANDACRE
with one exception that the various ganglia are arranged exactly as in Menidia. The exception is found in the case of the 9th nerve, which contains a special somatic or lateralis ganglion which is absent in Menidia. The visceral system (in horizontal shading, Fig. 1) is not differentiated into a general and special visceral system, but is left as shown in Professor Herrick's chart of Menidia.^ We find here general somatic gangUa (unshaded in Fig. 1) in the
Fig. 1. Reconstruction of the cranial ganglia of Ameiurus melas. Oc. 8, obj. 4mm, Spencer. Trigeminal, facial and anterior half of auditory from an embryo of 86 hours. The posterior half of the auditor3%the glossopharyngeal and the vagus from an embryo of 93 hours. General somatic ganglia imshaded; special somatic ganglia indicated by vertical shading; general and special visceral ganglia combined, indicated by horizontal shading.
5th or gasserian, and in the 10th. Special somatic gangUa (in vertical shading, fig. 1) supplying the ear and lateral line organs, are found in the 7th, 8th, 9th and 10th. General and special visceral ganglia are found in the 7th or geniculate in the 9th and in four divisions of the 10th. The general and special visceral ganglia, as mentioned above, cannot be separated in any type in the adult, and even in a late stage of development cannot be distinguished.
Starting with this type of ganglionic arrangement so conamon among the Ichthyopsida, let us inquire briefly how the various components are derived. In the region of the spinal cord, we have two components represented, the general somatic and the general visceral, both of whose ganglia are derived from the neural crest. In the head we have the general somatic and the general
The cranial and first spinal nerves of Menidia. Jour, of Com. Neu., fig. 3, 1899
COMPONENTS OF CRANIAL GANGLIA 73
visceral components present also, and these are derived exclusively in Ameiurus, and probably in other types, from the neural crest, so that for these two fundamental systems the cranial ganglia and spinal cord ganglia fall into one category, as far as their mode of origin is concerned. This fact tends to emphasize in this respect the essential similarity of the head and cord region rather than the priority of one over the other. Whatever type of specialization the head region may have imdergone — and the specialized ganglia furnish the same kind of evidence as that furnished by other structures — the two regions are essentially alike in these two fimdamental systems, both of which are very old phylogenetically and quite generalized. We need not conclude, however, that because these two systems are old phylogenetically and generalized and are represented in both cranial and trunk regions, that they stand in any genetic relation to specialized systems of ganglia, such as the special somatic and special visceral ganglia of the head.
In the discussion of the relation between general and special ganglia, the chief interest centers about the mode of origin of the special somatic and special visceral ganglia, which are peculiar to the cranial region and are not represented in the trunk.
It wiU be easier to follow the origin of the special visceral or gustatory ganglia first. It has been known for a long time that certain of the cranial ganglia derived from the neural crest come into contact with the lateral epidermis in at least two regions. The more dorsal of these regions is at the level of the auditory vesicle, at which point the epidermal thickenings are known as dorso-lateral placodes; and the more ventral of these regions is at the level of the dorsal portion of the gill slit, where the epidermal l^ckenings are known as epibranchial placodes. The majority of observers, however, have expressed doubt as to whether the epidermis contributes cells to the neural crest portion of the ganglia.
In Ameiurus, owing to the hypertrophied character of the gustatory ganglia and possibly to the precocious appearance of these ganglia, there can be no doubt that epibranchial placodes do contribute cells to the neural crest ganglia. These placodes are not mere contact points, but are true epidermal thickenings which
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F. L. LANDACRE
proliferate cells medially so that they are added in most cases en masse to the neural crest ganglia, and there is little cause for confusion as to their true nature. This mode of formation of the gustatory ganglia can be determined easily during the growth of the embryo in the case of the 7th and in the first two divisions of the 10th ganglia. The strongest confirmation comes, however, in the case of the epibranchial ganglion of the 9th nerv^e. In this nerve Professor Herrick can find only one t3^e of visceral fibers, the special or gustatory, and in the development of the 9th visceral ganglion the writer can find no trace of cells other than those that come from the placode, so . that one is warranted in concluding that the special visceral or gustatory ganglia come from the epibranchial placodes in Ameiurus. Every ganglion giving rise to gustatory fibers is derived in part from the placodes. This is true of the 7th, 9th, and four divisions of the 10th ganglia. (These are shown in cross-hatched shading in Fig. 2.) The fourth placode
Fig. 2. Ganglia as in fig. 1, to show the origin of the special visceral components. General somatic ganglia unshaded; special somatic ganglia indicated by vertical shading; general visceral ganglia indicated by horizontal shading; special visceral ganglia indicated by cross-hatched shading.
of the 10th ganglion had not appeared at the age at which this reconstruction wa's made. Further than this, the placodal derivative in each ganglion is in a general way proportionate to the number of gustatory fibers coming from the adult ganglion.
The last two placodal derivatives of the 10th ganglion are quite small, and the last one answers quite accurately to many of the descriptions of the epibranchial placodes in the literature. The last placode of the 10th does not appear until after the neural
COMPONENTS OF CRANIAL GANGLIA 75
crest ganglion comes into contact with the skin, and is in fact indicated only by the presence of this contact. If it were not for the characteristic relation presented by the 9th nerve and the almost equally characteristic relation shown by the first two divisions of the 10th, one could easily accept for the last division of the 10th, the usual description in regard to the relation of the placodes to the neural crest cells, namely, that the neural crest comes into contact merely with the epidermis. But with the history of the 7th, 9th and the first two divisions of the 10th, we must conclude that the usual description answers to a condition where the gustatory component in a ganglion is small or late in appearance, as in the mammals and in man particularly, and that probably the placodal contribution to the ganglion is not suflSciently large or suflSciently well defined to be isolated, and does not appear before the contact is formed between the neural crest ganglion and the epidermis.
We have then in Ameiurus evidence that the special and general visceral systems, which have been separated in the adult on the basis of the difference in the peripheral distribution and type of fibers, can be isolated in the embryo on the basis of mode of origin of the two types of ganglia. The special comes from the epibranchial placodes and the general from the neural crest. While this analysis of the ganglia cannot be made in the adult or even in a late stage of embryonic development, still the fact that they can be isolated in the earlier stages of their formation furnishes a striking confirmation of the analysis effected in the adult and tends materially to strengthen the point of view on which this analysis was made.
Turning now to the other special system of the head, the special somatic or acustico-lateralis, we find a somewhat different history with a rather sharp distinction between the mode of origin of pre-auditory and post-auditory components of this system. The last one of the series, the lateralis 10th, is derived exclusively from a dorso-lateral placode which is a posterior extension of the auditory vesicle. It becomes detached from the epidermis much as the epi-branchial ganglia do and contains no neural crest cells. The next two in the series, the lateralis 9th and the auditory, seem to come exclusively from the auditory vesicle but ow
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F. L. LANDACRE
ing to the congestion of structures in the auditory region caused by the rapidly developing vesicle, it is difficult to be certain of their purely placodal origin. They may possibly contain neural crest cells in Ameiurus and have been described by other authors as arising largely from the neural crest. If they do contain neural crest cells, they represent a transition between the lateralis 10th, which is a pure placodal gangUon, and the condition to be described in the lateralis 7th ganglion. Passing anteriorly, we come to the first one of the series, or rather the first two, the lateralis ganglia associated with the geniculate ganglion of the 7th, which is
Fig. 3. Ganglia as in figs. 1 and 2, shaded to show source of origin. Unshaded ganglia derived from neural crest; derivatives of dorso-lateral placodes indicated by vertical shading; derivatives of ventro-lateral placodes indicated by crosshatched shading.
pre-auditory in position. These two ganglia are derived exclusively from the neural crest and are totally unlike the lateralis 10th in their mode of origin.
We have thus as derivatives of the neural crest in the head all of the general visceral and general somatic gangUa of the 5th, 7th, 10th and the two special somatic ganglia associated with the geniculate ganghon of the 7th nerve. This is in rather striking contrast with the specific mode of origin of the special visceral ganglia, which are all derived from placodes, and at first glance seems to militate against the specific character of these gangUa as observed in the adult. But if one recall that the only condition imposed upon the nervous system, both peripheral and central, is that it shall furnish such correlations as will be profitable to the organism in adjusting it to its environment, it is not surprising
COMPONENTS OF CRANIAL GANGLIA 77
that sharp morphological distinctions should be rather frequently broken down. As illustrations of this, one has the dominance of certain centers in the brain as compared with the adjoining centers of similar characters: the usurpation by one nerve, of peripheral areas usually innervated by a totally different nerve and even by a different kind of component, or the dominating of a pure lateralis nerve such as the hyomandibular by components such as the general cutaneous and the visceral.
From a functional point of view, there is nothing unusual in the double mode of origin of the special somatic or lateralis ganglia of the head. As Professor Herrick has pointed out, the whole ectoderm of the head, particularly the dorsal and the lateral portions, is to be considered as potentially nervous. This is evidenced by the formation of the neuro-epithelium of the olfactory organ, by the formation of the ganglia from the epibranchial placodes and the dorso-lateral placodes, and by the formation of the neural crest ganglia and even of the cord itself. All the diverse modes of ganglion formation seem to serve equally well in connecting the peripheral sense organs with the central nervous system.
The olfactory neuro-epithelium, with, its sense cells acting as ganglion cells also, is evidently the simplest type of vertebrate ganglion. Next come the optic ganglionic cells which, while derived from the brain wall, still are only slightly removed from their epithelial origin. These ganghonic cells remain in the nervous layer and retain their position near their sense cells and do not migrate into the mesoderm. Following this, one has the auditory ganghon derived from the auditory pit but moving into the surroimding tissue and away from its sense cells. Its primitive character is evidenced by its bipolar ganglion cells and by the fact that its placode still remains a sense organ. Next, there is the lateralis ganglion of the 10th nerve, which comes from a placode but becomes entirely detached from it and hes in the mesoderm. In Ameiurus this placode, unlike the auditory placode, does not become a sense organ. It may possibly do so in other types, as Wilson maintains, and it would then resemble the auditory ganglion. Following this there are the epibranchial ganglia derived from
78 F. L. LANDACRE
placodes, concerning which there is no evidence in the ontogeny that these are sense organs at all. It seems probable, however, that in phylogeny they may have been derived from, or at least associated with, sense organs located at the dorsal portion of the gill slit, where the placodes now arise. If the epibranchial ganglia are included in this Ust tentatively, the whole class is characterized by the fact that they are associated more or less closely with special sense organs, which they afterward bring into contact with the brain, and thus serve to adjust the organism to its environment.
The neural crest gangha stand in rather sharp contrast with this large class of ganglia, in that they are not associated in origin with any type of special sense organ and conserve the functions of general sensibiUty rather than the special senses, except in the case of the lateraUs 7th ganglia, so that they can hardly be placed in a series with the first class. If the lateralis 7th gangha were derived originally from the placodes in Ameiurus, as they seem to be in Cyclostomes, and have changed from a placodal type to a neural crest type, it is rather a process of usurpation than of evolution.
The pre-auditory cranial region presents other modifications as compared with the post-auditory region fully as remarkable as this. The writer beUeves that the speciaUzed gangha should not be considered as derived from the unspeciahzed gangha in the sense that Johnston has shown the speciahzed centers of the brain to be derived from the unspeciahzed centers. These stand in a genetic relationship to each other. On the other hand, the placodal gangha have arisen in the potentially nervous ectoderm in response to the need of a more definite correlating apparatus and have come from the region of the sense organ. The neural crest ganglia have arisen in response to the same need, but have come from the region of the cord and brain. In the case of the preauditory laterahs gangha, the second type seems to have usurped the place and function of the first type and this may be going on even in the auditory and lateralis 9th. This change would be no more remarkable than other well known changes in the peripheral distribution and composition of nerves, which tend to adapt
COMPONENTS OF CRANIAL GANGLIA 79
the organism more accurately to its enviromnent, or to a different environment, or to integrate the activities of the organism itself. All of these changes, while presenting puzzling morphological conditions, tend to emphasize the idea that the functional needs of the organism rather than consistency in morphological detail is the key to the compUcated nervous mechanism of the vertebrates. The original characterization of a nerve component included the following distinctive points. The peripheral sense organs are of a common type with a common function. The fibers of a given component are usually of a definite size, thus enabling one to trace them through their ganglionic connections to the brain. The ganglia are definitely localized and sometimes in the most favorable types sharply isolated from the adjoining ganglia. The central ending of a given component is definitely localized. From the embryological evidence, we can add to this characterization the fact that the ganglionic components are definite in their mode of origin and except in the case of the preauditory lateralis ganglia are specific in their mode of origin. The general visceral and general somatic ganglionic components represented in both cranial and trunk regions are derived from the neural crest. The special visceral components are derived from the epibranchial placodes. The special somatic components show a transition from a pure placodal type in the lateralis 10th through a possible intermediate type in the lateralis 9th and auditory, to the pure neural crest type in the lateralis 7th.
4. THE PROBLEM OF THE CORRELATION MECHANISMS
JOHN B. JOHNSTON
University of Minnesota WITH ONE FIGURE
The next general problem before the anatomist of the nervous system is that of the correlation mechanisms. The organization of the primary receptive and effective mechanisms has found adequate expression in the doctrine of the functional divisions of the nervous system. The validity and the usefulness of this doctrine are demonstrated by its adoption by an increasing number of workers in this coimtry and abroad. The task of elaborating a complete functional morphology of the nervous system, however, has only been begim by the theory of fimctional divisions.
The problem of the correlating mechanisms is as many-sided and complex as the nervous system itself, as broad and varied as the whole of human life. The problem involves (1) all those questions relating to the structure and connections of the individual neurones, the character of the nerve impulse and the mode of its propagation through the neurone and from one neurone to another; continuity, synapses, stimulus threshold, summation, inhibition, etc.; and (2) all those questions r^arding the means by which simple reflexes are combined into larger actions directed for the welfare of the organism as a whole.
It is to the solution of the second set of problems that comparative neurology can contribute most at the present time. The problem is fundamentally more than all else a problem in the genesis of structures functioning in an adaptive manner. Structure and function can not be separated and both must be studied in the Ught of their purpose. Structures in action — actions performed by definite structures — have for their end the adaptation of the organism to the conditions of its Uf e. The way in which the parts
82 J. B. JOHNSTON
of the nervous system work together m directing the various organs for the welfare of the organism as a whole is the chief guide in the interpretation of the nervous system. This has been the burden of the teaching of the functional morphologist. But to discover how the parts of the nervous system work together it is necessary to inquire how the nervous mechanisms have come to be what they are through the process of evolution of the race. What were the first or simplest structures serving certain functions? How were they modified and speciahzed? What causes led to the increasing complexity of their structure? By what steps have they come to be what they are? In this way alone can we discover fully what they are and what they mean. For this way of looking at the nervous system we may use the name genetic method. It is in attacking the most complex problem that a complete genetic method is most needed. The study of the correlating mechanisms, to repeat, is a study of the evolution of nervous structures functioning in such a way as to secure the adaptation of the organisms concerned.
How have simple reflexes been combined into adaptive actionsystems? What are the impulse pathways by means of which one simple reflex is combined with others into a larger whole, while certain others are left passively idle and still others are actively shut out from participation because antagonistic to the main purpose? Nearly everyone of our common actions answers to this description, and those actions have grown up through a long past by the combination of simpler elements. We see this in the growth of the infant, in his learning to see things, to grasp objects, to walk, to talk; and we can more or less fully trace the phylogenetic history of some of our actions. The most direct and effective method of attack is to study the genesis of the actions themselves and the parallel genesis of the nervous mechanisms concerned in them. An excellent example of the right mode of approaching these problems is the study of the genesis of movements in amphibian tadpoles presented to this Association at its last meeting by Professor Coghill.
Among the many phenomena requiring explanation, the spread of reflexes to distant segments and the cooperation of distant seg
THE PROBLEM OF THE CORRELATION MECHANISMS 83
ments in a single action will illustrate the point of view here suggested. Perhaps the most constant result in experiments upon animals is the tendency for the responses to be complete or partial reproductions of habitual or common acts. In the highly specialized reflexes of the dog certain kinds of stimulation produce definite movements. For example, stimulation of the shoulder in any of several ways calls forth the scratch-reflex. It is frequently noticed, when the limbs are called into action by a stimulus, that the form of their movement is dominated by the method of progression characteristic of the given animal. Thus in the dog various forms of excitation produce attitudes of the limbs which are due to the dominance of the trotting gait in this animal. If the stimulation be at a hind foot the movement of the fore leg or legs is that which would form part of the act of trotting. If painful stimulation of one hind foot in the spinal dog be continued the flexor muscles of that leg contract and the other three legs move in the rhythm of progression, that is, the hurt foot is held up and the other three feet run away (Sherrington, Integrative Action, p. 240). So, in experiments on lower vertebrates in which general somatic nerves are stimulated, the responses are movements of swimming. Witness the recent work of Sheldon on chemical stimulation of the dogfish. If the stimulation is strong enough it calls forth contraction of muscles of distant segments, perhaps of all segments of the body. In this spread of reflexes to distant segments we have one of the fundamental elements in the combination of reflexes.
The responses called forth by irradiation to distant segments through the spinal cord are not hap-hazard, but are parts of typical actions. The phenomena of irradiation must therefore rest upon systems of nerve paths produced in the course of the evolution of characteristic behavior of the given species. Long spinal irradiation is but a specific illustration of what we may call segmental, or metameric correlation.
When we look for the mechanism of this segmental correlation, we find a plethora of materials and our diflSculty is to sift out definite structures and discover their specific functions. In the spinal cord and brain of vertebrates we recognize in each of the
84 J. B. JOHNSTON
receptive columns, somatic and visceral, primary receptive neurones and other neurones {substantia reticularis) which constitute the structural means for correlation. Fibers arise from the somatic receptive colunm — the dorsal horn — to go to other segments to end in the same column on the same or opposite side. Other fibers go to the somatic motor column of one or more segments. These latter may serve to call into action larger masses of muscle, but can have only a low value in correlation.
Those neurones by which the in-coming impulses are spread to distant segments of the same column are of especial significance in correlation. Two chief sets of such neurones are recognized. The fibers of one of these run up or down the cord in proximity to the dorsal horn itself into which the fibers turn after a longer or shorter course. The second set of neurones send their fibers by way of the ventral decussation of the cord to end in the dorsal horn of the opposite side in a higher or lower segment.
Whatever may be the specific mode of functioning of the correlation neurones within the spinal cord, numerous long fibers of both sets of neurones have played an important part in the evolution of the brain. Homolateral fibers from the dorsal horn of the cord reach the cerebellum and many more join these from the nuclei cuneatus and gracilis of the medulla oblongata. These direct cerebellar fibers are joined also by external arcuates from the other side of the medulla oblongata. Crossed fibers from the dorsal horn of the cord together with many more from the nuclei in the oblongata, including the centers for the fifth and eighth nerves, and still others from the dentate nucleus of the cerebellum, form a great system or several systems of fibers, of which the medial lemniscus is the type. The fibers of both direct and crossed systems pass from the somatic sensory column of lower segments to the same column in higher segments. These are fundamentally segmental correlation fibers, but their great numbers and their definite arrangement with reference to certain segments and nuclei in the brain are due to a special significance which they have obtained in consequence of the development of special sense organs.
It is customary to speak of the development of organs of special sense in the head as the cause of the development of the brain.
THE PROBLEM OF THE CORRELATION MECHANISMS 85
Hum
n term .
e>a.
SCHEMA OF SBQMBNTAL CORRBLATINQ TRACTS
On the left are shown some of the long ascending tracts concerned in somatic receptive fimctions in man. On the right is shown the segmented brain of a hypothetical primitive or ancestral form in which the evagination of the forebrain and the retinal areas has begun. Otherwise the brain is simply the anterior portion of the neural tube. In the arrangement of the direct and crossed correlating fibers the specialized tracts of true vertebrates are foreshadowed. The place of ending of the nervus terminalis in this figure is the primordial somatic cortex.
86 J. B. JOHNSTON
This is true, but we are too apt to lose sight of the importance of the correlation of general somatic sense organs with the special sense organs. The primary receptive centers for the eye, ear and nose account for only a small part of the increased size of the anterior part of the neural tube. The greater part of the enlargement called the brain is due to the material serving for correlation between eye, ear, and nose and between those and the skin and muscles of the body.
The mechanism for correlation of the general bodily organs with the organs of special sense was ready-prepared before those sense organs made their appearance in the vertebrate ancestors. The ancestral forms had no head, only an anterior end. What is now head was in those ancestors a region with a complete series of segments and sensory nerves. We have no evidence of somatic motor nerves further forward than the present oculomotorius. Two forms of sensory neurones were present : one which we may call the ganglion-cell type, sensitive especially to mechanical stimuli, with chemical, photic and thermal sensitiveness in the background; the other which came to form the olfactory organ, with chemicar sensitiveness dominant. Both these had been derived perhaps from a single still more ancient and unspecialized type of peripheral sense cells. The speciaUzation of the sense cells in the anterior segment of the body as cells of chemical sense and their collection into a restricted area gave rise to the first special sense organ, the olfactory. The sense cells of the rest of the body likewise collected into a long strip at either side of the neural plate and gave rise to the spinal and cranial ganglia. In this simple animal the chief long paths in the nervous system were concerned with segmental correlation and these paths form the basis for the high development of correlation mechanisms, which is the chief characteristic of vertebrate animals and which enabled this phylum, by adapting itself to wider and wider ranges of environmental conditions, to become the dominant race of animals.
A certain part of the ganglion-cell type of sensorj'^ neurones, especially in the anterior end of the body, from the first tended to specialize in the direction of light percipient cells and in three or more segments of the head these cells became aggregated into eyes.
THE PROBLEM OF THE CORRELATION MECHANISMS 87
These formed parts of the bram wall and became evaginated, as is well known. I have several times brought forward evidence that the eyes were developed from the general somatic receptive column and I have suggested that the optic tract fibers constituted essentially a correlation tract comparable to the lemniscus. The most important result following from these facts is now to be*pointed out, namely, that this optic tract entered the somatic sensory column where its impulses came at once into relation with impulses from the skin and muscles, brought up by the long tracts for the sake, originally, of segmental correlation. Thus early the primordial structiu-es were present which provided against the dominance of direct and unmodified reflexes, such as obtains in invertebrates, and provided for the control of body movements by the cooperation of two or more sensory mechanisms taking account of different factors in the environment. This it is which distinguishes all vertebrates from invertebrate forms, — the degree to which the power to guide their actions with reference to impulses of two or more kinds is developed.
When later, the acustico-lateralis system of sense organs arose to take account of slow wave-stimulation and developed into an organ of the static sense, and still later gave rise to an organ of hearing, these organs sent their impulses into the same somatic sensory column, whose long tracts served also for correlation of these with the skin and muscles.
It was in this way that the brain came to be developed as a great collection of correlation centers. The gray matter in the tectum and the thalamus, as soon as the eye was formed, served at once, not as optic centers alone, but as somatic-optic correlation centers. It is noticeable that the fishes which present well formed optic centers in the thalamus are not alone those with large eyes but the strong-swimming, active forms. For example, among ganoids the active and predacious freshwater dogfish (Amia) has a well developed lateral geniculate body, while the sluggish bottom-feeding sturgeon has not.
Again, the gray matter in the segments following the tectum became a center for the correlation of canal-organ impulses with those of the muscle sense in the control of muscular move
88 J. B. JOHNSTON
ments. Here was developed the most sharply specialized and highly characteristic region of the vertebrate brain, the cerebellum, Deiter's nucleus and area acustica serving as a static mechanism, an organ for muscle tone, etc. The great importance to this mechanism of the sensory impressions from the muscles and the skin which ate carried up by the dorsal tracts and restif orm bodies, has been so often pointed out that we need not dwell on it here.
Further, the common and primitive basis of correlation tracts which put these sense organs into relation with the muscles and skin, served also to put them into relation with one another. This must be passed over for the sake of discussing briefly the conditions determining the development of the somatic cortical centers in which correlation of all these sense surfaces is brought about, and apparently on a higher plane.
The cerebral cortex consists essentially of two parts, a visceral cortex and a somatic cortex. The former will be discussed in another paper. Here let us examine briefly the conditions for the development of the somatic cortex. In the more active lower vertebrates the optic-somatic correlation centers play so important a part in the more intelligent seeming activities that some one has said that the tectum plays the part of cortex for the fish. Why have not some of the lower correlation centers, say the optic, developed into the cortex? Chiefly for the reason that the presence of the special sense organ demands the use of the greater part of the substantia reticularis in those centers for the direction of simple or combined reflexes in which the impulses from one sense organ play a dominant rdle. It is characteristic of cerebral cortex that it is free from the domination of any one kind of sensory impulses. Since there is some limit to the development of any correlation center — at least the Umit of the power of growth with which that part of the nervous system is endowed in the embryo — a center which is largely concerned with any one sense could not well supply the material for cortical functions.
An influence favoring the development of cortical centers in the telencephalon is the presence of the olfactory centers in that segment. The olfactory organ is not only a special organ of the chemical sense of ancient standing, but it has acquired special
THE PROBLEM OF THE CORRELATION MECHANISMS 89
importance by reason of its power to function at a distance. As pointed out by Sherrington, the olfactory organ is a distance receptor in the search for food. It is important, therefore, that the olfactory organ be correlated with the visual organ and with the muscles which are chiefly concerned in the capture of food. WTiere is this correlation provided for? In part at least in the olfactory centers in the hypothalamus and epithalamus and the optic centers with which these are inter-connected. Indeed, these socalled olfactory centers in the diencephalon are in reaUty the meeting-places or clearing-houses for impulses of different sorts and should be called olfacto-gustatory, olfacto-visual and olfactomuscular correlation centers. I see no reason why these centers should not have suflSced for the combination of all sorts of reflexes in which the olfactory organ was concerned as a distance receptor in the search for food. The most that we can say as to the influence of the olfactory organ is that an olfactory-somatic correlation center in the telencephalon would perhaps have some advantage in eflSciency. The presence of the olfactory organ does not give any cley as to how such a center in the telencephalon came to arise. -^
For this we must turn to the principle of metameric correlation. The long correlation tracts are believed to be more fundamental and of earlier origin than the special sense organs or the brain itself, and if such tracts reached the first brain segment regardless of the olfactory organ, then the development of an olfacto-somatic correlation center in the telencephalon is merely a question of its usefulness to the organism. Was there present in the first segment of the neural tube of vertebrate ancestors a segment of the somatic sensory colunm? Was this connected with lower segments of the same colunm by metameric correlation tracts? And could such a center offer the material and the conditions for the development of the somatic cortex? I believe all these questions are to be answered in the aflirmative.
There is connected with the forebrain in selachians a nerve, evidently vestigeal, which bears a ganglion and is distributed to the epitheUum of the nasal sac. I believe that this represents the general cutaneous nerve component of this segment. The nerve
90 J. B. JOHNSTON
enters a part of the forebrain which in selachians receives fiber tracts from lower segments of the somatic sensory column, namely, the lenmiscus center in the thalamus and perhaps other centers. Here are evidences of the existence of a primary somatic sensory center and of correlatmg tracts in one of the lower groups of fishes. That ancestral vertebrates possessed a cutaneous nerve in the first segment and that its center was connected by long tracts with lower centers of the same sort is a reasonable deduction from this evidence and also is a priori very probable.
Such a center was very favorably placed for the development of somatic cortex for two chief reasons. First, it had the advantage of proximity to the olfactory centers and the olfacto-gustatory cortex. Second, the correlating material of this segment of the somatic sensory column was the only one to be set free from the dominance of a special sense organ ; eye, ear, skin, or muscles. The N. terminalis disappeared and the cutaneous surface which it suppUed was invaded by the trigeminus. The substantia reticularis of the forebrain center, was then released from the work of combination of simple reflexes and came to serve for correlations of a higher order. This is a special case of a general tendency in the brain which has long been recognized, namely, the tendency toward segregation and condensation of centers for special functions. The cutaneous innervation of the head, originally provided by some ten or eleven segmental nerves, is in man almost all provided by the trigeminus with some branches from the first and second spinal nerves, and its center is condensed into the medulla oblongata. The special sense organs were restricted to one or a few segments from the first and have dominated those segments, as we have seen. The forebrain segment of the somatic colunm, while losing its primary sensory function, offered the opportunity for olfacto-somatic correlation and for the inter-correlation of somatic organs which sent impulses up to it over the long tracts. It can not be thought that the occasion or impulse for the development of this correlating center after it was freed from its primary sensory function was suppUed by the olfactory organ and centers alone. Olfacto-somatic correlation in the forebrain is to be regarded rather as incidental. Had there been no other occasion
THE PROBLEM OF THE CORRELATION MECHANISMS 91
for a somatic center in the forebrain, olfacto-somatic correlation would all have been cared for in the diencephalon. The cerebral cortex serves for correlation between tactile, muscular, static, auditory and visual impulses in a thousand ways in which olfactory impulses are not at all concerned. For the development of these somatic correlating functions the olfactory apparatus could have been neither the stimulus nor the directing force. If there had been no somatic sensory center in the forebrain, the somatic cortical functions would never have been located in the telencephalon. The determining factors in the development of the somatic cortex were: (1) the center for the nervus terminalis with the substantia reticularis belonging to it; (2) the fimdamental correlation tracts bringing up tactile, musculo-sensory and visual impulses to this center; (3) the reduction of the nerve which left the substantia reticularis free to serve for correlation of the impulses just mentioned; (4) and the advantage of a center where impulses of different kinds might interact upon equal terms. In this last, which seems at first a vague and intangible principle, lies the very essence of the conditions for the development of the higher cortical functions, memory, judgment, reasoning and the aesthetic faculties. Consciousness springs, as I believe, from the tension of indecision between two or more sets of impulses, any one of which coining alone would be followed by a simple reflex; or between two or more possible responses to a stimulus. If so, we can not expect a very high grade of consciousness in animals in whose nervous systems each center is under the dominant influence of one sense organ. The tension in the olfacto-visual, olfacto-gustatory, or visuo-muscular correlation centers would, too often, be dissolved by the dominant influence of one or other sense organ. Inhibition would not be very prolonged, one set of conditions would not hold the attention long for the purpose of weighing the difi'erent impulses or responses over against one another. The solution of the tension through a simple reflex or a combination of reflexes of a low order or of a habitual type would be unfavorable to the development of memory, of adaptability in responses, or of deliberation, which is essential to intelligent action.
92 J. B. JOHNSTON
In the forebrain center, however, just those conditions are presented which are favorable to the development of the faculties of intelligence. In addition to the freedom from the unequal influence of one set of impulses, the fact that impulses reach this center only by long paths and usually by a relay of three neurones is of great importance. In the definition of cortex in general I have elsewhere given weight to the relay of three neurones for these reasons: (1) Such a relay removes the cortex farther from the realm of direct reflexes by increasing the time of reaction through the cortex. The cortex is never involved where extraordinarily quick response is necessary. (2) The relay restricts the number of impulses passing to the cortex. Impulses to reach the cortex either must have suflBcient energy to connnand the right of way (through the synapses) or they must find the way prepared for them through attention; and attention itself is a conscious process and one of the greatest factors in the further development of consciousness.
If we were to look at the visceral sensory mechanisms we should find essentially the same arrangements as have been described for the somatic: a longitudinal colunm with long tracts connecting distant segments with one another. Into this column came the fibers of taste and smell and the long tracts brought these into relation in the forebrain, so giving rise to the visceral cortex.
I present, then, as three matters of great importance in the study of the correlation mechanisms: (1) the fundamental chai'acter of metameric correlation; (2) the development of the brain through the local hypertrophy of this segmental mechanism under the influence of the special sense organs, and the related segregation of special centers, and (3) the indifference of the somatic correlation center in the telencephalon, which offers the essential condition for the development of the cerebral cortex as the organ of conscious life.
PROCEEDINGS OF THE AMERICAN ASSOCIATION OF ANATOMISTS
TWENTY-FIFTH SESSION
In the Embryological Laboratory, Harvard Medical School, Boston, Massachusetts, December 28, 29, and SO, 1909.
Tuesday, December 28, 9.30 a. m., to 1.00 p. m.
The twenty-fifth session was called to order at 9.30 am. by President, James Playfair McMurrich, who appointed the following conmiittees.
Committee on Nominations; Charles S. Minot, Chairman; Thomas G. Lee, Simon H. Gage.
Avditing Committee; Milton J. Greenman, Chairman; August G. Pohlman.
Symposium of Comparative Neurology:
George H. Parker, Harvard University. The phylogenetic origin of the nervous system.
C. Jfdson Herrick, Xjniversity of Chicago. The relations of the peripheral and central nervous systems in phylogeny.
Francis L. Landacre, Ohio State iJniversity. The origin of the sensory components of the cranial ganglia.
John B. Johnston, University of Minnesota. The problem of correlation certers and the evolution of the cerebral cortex.
The general discussion was opened by Henry H. Donaldson, Wistar Institute of Anatomy.
The remainder of this session was devoted to the presentation of the following neurological papers:
Stewart Paton, Princeton y New Jersey. Neurofibrillation in relation to the first
movements of vertebrate embryos. Susanna Phelps Gage, Ithaca, New York. A pair of dorsal cerebral sacs on
either side of the terma in a 35 day and other human embryos, comparable
with the cerebral sacs in fishes. S. Walter Ranson, Northwestern University Medical School. Non-medullated
nerve fibers in the spinal nerves.
94 AMERICAN ASSOCIATION OF ANATOMISTS
Henry H. Donaldson, Wistar Institute of Anatomy. On the percentage of water in the central nervous system of the albino rat. (Lantern slides.)
S. Hatai, Wistar Institute of Anatomy. Preliminary report on the inheritance of the weight of the central nervous system in rats.
John B. Johnston, University of Minnesota. Early stages in the evolution of the cerebral cortex. (Only an abstract presented.)
The following neurological papers announced were read by title:
C. JuDSON Herrick, University of Chicago. The analysis of the paraterminal body and its relation to the hippocampus in lower brains.
Burt G. Wilder, Cornell University. The weight and form of the brain of some American negroes; illustrated by specimens, photographs and charts.
Elizabeth H. Dunn, University of Chicago. Some findings regarding the distribution of splitting medullated nerve fibers in the peripheral nervous system.
Tuesday, December 28, 2 to 5 P. M. Demonstrations as follows:
Charles R. Essick, Johns Hopkins University, (a) Specimens showing the development of the arcuate nuclei in the human embryo; (6) Dissections to show migration of cells in the medulla of the pig embrvo.
Susanna Phelps Gage, Ithaca, New York. Models of the head of a five-weeks human embryo.
Clarence M. Jackson, University of Missouri. Models of the thoracic and abdominal viscera of the human embryo.
John B. Johnston, University of Minnesota. Models illustrating the cortical areas in fishes and amphibians.
Frederick T. Lewis, Harvard Medical School, (a) The first Ijonph glands in rabbit and human embryos. Specimens and models illustrating tae relation of the atrioventricular valves to the interventricular foramen.
Stewart Paton, Princeton^ New Jersey. Preparations showing neurofibrillation in relation to the first movements of the vertebrate embryo.
William S. Miller, University of Wisconsin. Reconstruction models showing the arrangement of the cartilages in the trachea and bronchi of the Guinea pig. (6) Arrangement of the muscle in the trachea and at the carina tracheae in various animals.
S. Walter Ranson, Northwestern University Medical School. Sections of the human sciatic nerve showing non-medullated nerve fibers.
Florence R. Sarin, Johns Hopkins University. Specimens showing the development of the structural unit in the embryo pig's spleen.
J. Parsons Schaepfer, Cornell University Medical School, (Ithaca, New York). Modelft showing the development of the lateral wall of tne nasal cavitv iii man.
Harold D. Senior, College of medicine, Syracuse University. A method of obtaining orientation points in serial sections, for use in plastic reconstructions.
Charles F. Silvester, Princeton University. Preparations showing the presence of permanent lymphatico-venous communications at the renal level in the South Araierican monkey.
George L; Streeter, University of Michigan. Demonstrating for (a) F. H. Busby. Models showing the topography of the cerebral cortex of the opossum. (6) J. H. Stokes. Two models, showing the facial, vestibular and cochlear nerves with their central connections in the opossum.
(c) H. A. Calhoun. Models of the medulla oblongata of the opossum.
(d) H. W. Stiles. Model showing the Ventricular system of the brain of the opossum.
(e) H. N. T. Nichols. Double spinal ganglia.
John L. Bremer, Harvard Medical School. Demonstration of unit room No. 203, showing equipment and material used in the first year's course in Embryology and Histology in the Harvard Medical SchooL
PROCEEDINGS 95
Members of the staff demonstrated models illustrating vertebrate development; made by students in the Harvard Laboratory of Comparative Anatomy.
Wednesday, December 29, 9.30 a. m. to 1 p. m. Session for
THE reading of PAPERS, FlRST ViCE-PrESIDENT WiLLIAM S.
Miller and President James Playfair McMurrich, presiding.
Elexious T. Bell. University of Missouri. On the staining of fat in muscle fibers.
Victor E. Emmel, Washington University Medical School. Observations on the differentiation of regenerating epidermal and striated muscle tissue in the lobster.
Arthur E. Hertzler, Kansas City, Missouri. The formation of fibrous tissue.
George S. Huntington, Columbia University (New York City). The development of the thoracic ducts in embryo of the cat (with lantern slides).
Edwin G. Conklin, Princeton University. Cell size and nuclear size.
Jeremiah G. Ferguson, Cornell University Medical School (New York City), 1. The hypobranchial arterial system in the Selachiae. 2. The thyroid gland of elasmobranchs, with special reference to its Vascular supply.
Clarence M. Jackson, University of Missouri. Electric heating for laboratory apparatus.
The following papers announced on the program were read by title:
Charles S. Mi not, Harvard University. Notes on an early stage of pregnancy.
Herbert M. Evans, Johns Hopkins University. Note on the development of the superficial arteries of the nead in the human embryo; especially the occipitalis, auricularis posterior and temporalis superficialis.
Harvey E. Jordan, University of Virginia. A further study of the human umbilical vesicle.
William F. Mercer, Ohio University. Development of the metacarpal bones in the leg of the sheep.
12 to 1. Address by Professor Doctor Franz Weidenreich of Strassburg, Germany, On the morphology of the blood cells and their relation to each other. (Die Morphologie der Blutzellefi und ihre Beziehungen zu einander.)
This address, given at the invitation of Professor Minot and the Executive Committee, was delivered in German. At its conclusion, the Association extended Professor Weidenreich a vote of thanks and appreciation.
Wednesday, December 29, 2 to 4 p. m. Demonstrations AS follows:
Elexious T. Bell, University of Missouri. Preparation showing fat in muscle
fibers. Victor E. Emmel, Washington University Medical School. Preparations showing
the differentiation of regenerating epidermal and striated muscle tissue in the
lobster.
96 AMERICAN ASSOCIATION OF ANATOMISTS
Jeremiah S. Febguson, Cornell University Medical School (New York City), (a) Dissection of the hypobranchiai system of the dogfish. (6) Sections and total mounts of the thyroid gland of elasmobranchs.
George S. Huntington, Columbia University and C. F. W. McClure, Princeton University. Models illustrating the development of the jugular lymph sacs in mammalia.
Arthur E. Hertzler, Kansas City Missouri. Pieparations and drawings showing the formation of fibi ous tissue.
Professor Doctor Weidenreich. — A demonstiation of a seiies of pieparations showing the morphology of the blood cells and their relation to each other.
Wednesday, December 29, 4 p. m. Business Meeting.
On motion, the minutes of the Secretary as published in the Anatomical Record, Vol. Ill, No. 1, page 62 to 74, were approved. The Treasurer made the following report for the year 1909:
Total receipts for the year 1909 S1381 .20
Balance on hand December 24, 1908 172 . 17
Total $1553.37 $1553.37
Expenses of the Secretary. Baltimoie meeting $32.40
Smoker, Johns Hopkins Club 7 .60
Postage and envelopes 26.20
Wistar Insi itute of Anatom> for 275 subscriptions to American Journal of Anatomy and Anatomical Record at
$4.50 1237.50
Printing 19.40
Total $1323.10 1323.10
Balance on hand December 23, 1909, deposited in the Farmers and Mechanics Bank, Ann Arbor, Michigan $230. 27
August G. Pohlman reported for the Auditing Committee: We have examined the accounts of G. Carl Huber, SecretaryTreasurer for the year 1909 and found them correct."
On motion the reports of the Treasurer and of the Auditing Committee were accepted and adopted.
James Playfair McMurrich and Ross G. Harrison, members from this Association of the International Committee on Reformation of Myological nomenclature, reported progress. The committee was continued.
The Committee of this Association, consisting of Charles S. Minot, Franklin P. Mall, James Playfair McMurrich, G. Carl Huber, George A. Piersol, George S. Huntington, in charge of arrangements for the International Congress of Anatomy to be
PROCEEDINGS 97
held in Brussels, August 7 to 11, 1910, through its Chairman, Dr. Minot, reported progress.
The following were recommended by the Executive Committee for election to membership in the Association.
Robert P. Bigelow, Ph.D., Instructor in Biology and Librarian, Massachusetts
Institute of Technology. David Cheever, A.B., M.D., Demonstrator of Anatomy, Harvard Medical School, H. K. Corning, M.D., Professor of Anatomy, Basely Switzerland. Victor E. Emmel, Ph.D., Instructor in Histology and Embryology, Wc^hington
University^ St. Louis. Frederick Etherington, M.D., Professor of Anatomy, Queen* s University^ Kingston, Canada. William S. Halsted, M.D., Professor of Surgery, Johns Hopkins University. Davenport Hooker, M.A., Instructor in Anatomy, Medical Department, Yale
University. Franklin P. Johnston, A.B., Austin Teaching Fellow, Harvard Medical School. 3. F. McClendon, Ph.D., Assistant in Histology, Cornell University Medical
School, New York. Max Morse, Ph.D., Instructoi in Biology, College of the City of New York. Ernest Sachs, A.B., M.D., Physician and Surgeon, New York City. Daniel M. Shoemaker, B.S., M.D., Associate Professor of Anatomy, St. Ijouis
University. James M. Stotsenburg, M.D., Curator and Junior Associate in Anatomy,
Wistar Institute. Frederick Tilney, A.B., M.D., Associate in Anatomy, Columbia University,
New York City. I^ouis Hill Weed, A.M., Johns Hopkins Medical School. Baltimore. Franz Weidbnreich, M.D., a.o., Protessor and Prosector of Anatomy, Strass hurg, Germany.
On motion, the Secretary was instructed to cast a ballot for election to membership in the American Association of Anatomists of applicants recommended by the Executive Committee. Carried.
The Association then proceeded to the consideration of the constitution placed before this Association at its last meeting by the committee on revision of the constitution, consisting of G. Carl Huber (Chairman), Henry H. Donaldson and Robert R. Bensley, and sent to each member at least one month in advance of this meeting as provided for in Section 2, Article VII, of the constitution.
On motion, the constitution proposed by the committee was considered article for article. Each article was voted on separately and adopted as proposed or as amended. In conclusion the entire constitution was unanimously adopted as a whole, in the following form:
98 AMERICAN ASSOCIATION OF ANATOMISTS
CONSTITUTION.
ARTICLE I
Section 1. The name of the Society shall be "The American Association of Anatomists.
Sec. 2. The purpose of the Association shall be the advancement of anatomical science.
ARTICLE n
The officers of the Association shall consist of a President, a Vice-President, and a Secretary, who shall also act as Treasurer. The President and the Vice-President shall be elected for two years, the Secretary for four years. In case of absence of the President and Vice-President, the senior member of the Executive Committee shall preside. The election of all the officers shall be by ballot.
ARTICLE III
The management of the affairs of the Association shall be delegated to an Executive Committee, consisting of eleven members, including the officers. Two members of the Executive Committee shall be elected annually, and, so far as possible, election of members of the Executive Conmiittee shall be in proportion to the geographical distribution of members. Five shall constitute a quorum of the Executive Committee.
ARTICLE IV
The Association shall meet at least annually, the time and place to be determined by the Executive Committee. The annual meeting for the election of officers shall be the meeting of convocation week, or in case this is not held, the first meeting after the new year.
ARTICLE V
Section 1. Candidates for membership must be persons engaged in the investigation of anatomical or cognate sciences,
PROCEEDINGS 99
and shall be proposed in writing to the Executive Conunittee by two members, who shall accompany the recommendations by a list of the candidate's publications, together with references. Their election by the Executive Committee, to be effective, shall be ratified by the Association in open meeting.
Sec. 2. Honorary members may be elected from those who have distinguished themselves in anatomical research. Nominations by the Executive Conmiittee must be unanimous and their proposal with a reason for recommendations shall be presented to the Association at an annual meeting, a three-fourths vote of members present being necessary for an election.
ARTICLE VI.
The annual dues shall be five dollars. A member in arrears for dues for two years shall be dropped by the Secretary at the next meeting of the Association, but may be reinstated at the discretion of the Executive Committee on payment of arrears.
ARTICLE VII.
Section 1. Twenty members shall constitute a quorum for the transaction of business.
Sec. 2. Any change in the constitution of the Association must be presented in writing at one annual meeting in order to receive consideration and be acted upon at the next annual meeting; due notice of the proposed change to be sent to each member at least one month in advance of the meeting at which such action is to be taken.
Sec. 3. The ruling of the Chairman shall be in accordance with ^'Robert's Rules of Order.
The orders adopted by this Association, which read as follows, were not altered :
Newlv elected members must qualify by pajrment of dues for one year within thirty days after election.
The maximum limit of time for the reading of papers shall be twenty minutes.
The Secretary and Treasurer shall be allowed his tiaveling expenses and the sum of $10 toward the payment of his hotel bill, at each session of the Association.
That^ihe Association discontinue the separate publication of its proceedings and that the Anatomical Record be sent to each member of the Association, on payment of nis annual dues, this journal to publish the proceedings of the Association.
100 AMERICAN ASSOCIATION OP ANATOMISTS
Charles S. Minot, as Chairman of the Committee on nominations, placed before the Association the following nominations:
President George A. Piersol.
Vice-President, Charles F. W. McClure.
Secretary 'Treasurer, • G. Carl Huber.
For Members of the Executive Committee.
Irving Hardestt, Robert J. Terry,
Warren H. Lewis, Frederick T. Lewis.
On motion, the Secretary was instructed to cast a ballot for the election to the respective offices of the members nominated by the Committee on nominations.
Charles S. Minot moved ^'That the American Association of Anatomists recommend to the International Congress of Anatomy the appointment of an International Committee to revise embryological nomenclature and prepare a list of standard terms. Seconded and carried.
On motion of Thomas G. Lee, the business meeting was adjourned.
Thursday, December 30, 9:30 a.m. to 1 p.m. Session for the
READING OF PAPERS, SeCOND ViCE-PrESIDENT, FLORENCE R.
Sarin, and the President, James Playfair McMurrich,
PRESIDING. The FOLLOWING PAPERS WERE PRESENTED:
J. F. McClendon, Cornell University Medical School {New York City). The toti potency of the first two blastomeres of the frog's egg. J. Parsons Schaeffer, Cornell University Medical School (Ithaca). Or the genesis
of air cells in the nasal conchae. George S. Huntington and H.v.W. Schulte, Columbia University (New York
City). Contribution to the morphology of the mammalian salivary glands.
1. H. v. W. Schulte. Development of the salivary glands of the cat.
2. George S. Huntington. Anatomy of the salivary glands in primates. (Only a brief abstract presented.)
Leo Loeb and William F. H. Addison, University of Pennsylvania. The transplantation of skin of the Guinea pig and the pigeon into other species. Charles R. Stockard, Cornell University Medical School (New York City).
1. The influence of alcohol and other anaesthetics on the developing embryo.
2. The independent origin and self differentiation of the crystalline Tens. George L. Streeter, University of Michigan. A new method of dissection of
the spinal cord and brachial plexus (Lantern slides).. Robert J. Terry, Washington University Medical School. The morphology of the
pineal region in fishes. John Warren, Harvard Medical School. On the paraphysis and*pineal region in
lacerta and chrysemis marginata.
PROCEEDINGS 101
Franklin P. Johnston, Harvard Medical School, Development of the glands and
villi of the human digestive tract. Leonard W. Williams, Harvard Medical School. The somites of the chick. James Murphy, Johns Hopkins Medical Scliool. On the relation of the sulcus
lunatus to the visual area in the negro and white brains. G. Carl Huber, University of Michiaan. (Only brief abstracts presented).
1. On the relation of the notochord to the anlage of the pharyngeal bursa.
2. A note concerning the caudal end of the notochord in human embryos.
3. Concerning embryonic remains of the caudal end of the neural canal in the human embryo.
The following papers announced were read by title :
Charles F. Silvester, Princeton University, On the presence of permanent lymphatico-venous communications at the renal level in the South American monkeys.
Frederick Tilney, Columbia University (New York City). Comparative histology of the hypophysis.
Charles R. Bardeen, University of Wisconsin. Pi actical state board examination in anatomy.
Owing to the absence of Dr. Bardeen and at the suggestion of the Executive Conmiittee, the Association voted that Dr. Bardeen's paper be printed in the Anatomical Record and that the President appoint a committee to collect data and consider the question of State Board examinations and report to this Association at a future meeting.
The President appointed as such Committee, Charles R. Bardeen (Chairman), Franklin P. Mall, and George A. Piersol.
Thursday, December 29, 2 to 5 p.m. Demonstrations AS follows:
Robert J. Terry, Washington University Medical School, (a) Specimens and drawings illustrating the morphology of the pineal region in teleosts. (6) The velum trans versum of Opsanus, a true choroid plexus.
John Warren, Harvard Medical School. Models showing the paraph ysis and pineal region in lacerta and chrysemis marginata.
CHARLEe R. Stockard, Cornell University Medical School (New York City.) A sagittal section of a 2.2 mm. human embryo with 8 primitive se^ents.
H. V. W. ScHULTE, Columbia University (New York). Preparations illustrating the development of the salivary glands in the cat.
Clarence M. Jackson, University of Missouri. Electric heater and thermoregulator for paraffin ovens.
Leo Loeb and William H. F. Addison, University of Pennsylvania. Microscopic preparations of the skin of Guinea pig and pigeon after transplantation to other species.
Franklin P. Johnson, Harvard Medical School. Models showing the development of glands and villi of the human digestive tract.
102 AMERICAN ASSOCIATION OF ANATOMISTS
Charles A. Todd, Washington University Medical SckooL Specimens illustrating a plan for a human anatomical museum.
G. Carl Huber, University of Michigan. Prepaiations showing (a) The relation of the notochord to the anlage of the pharyngeal bursa; (6) The caudal end of the notochord in human embryos ; (c) Embryonic remains of the caudal end of the neural canal in human embiyos.
G. Carl Huber, Secretary'Treasurer, American Association of Anatomists.
AMERICAN ASSOCIATION OF ANATOMISTS
OFFICERS AND LIST OF MEMBERS
Officers
President George A. Piersol
Vice-President Charles F. W. McClure
Secretary-Treasurer G. Carl Huber
Executive CammiUee
Thomas G. Leb, Irving Hardbstt,
Simon H. Gagb, Robert J. Terry,
Robert R. Bbnblet, Warren H. Lbwis,
Henrt H. Donaldson, Frederick T. Lewis.
COBfMITTEES
Committee of Arrangements from this Association for IrUemcUional Congress of
Anatomy f Brussels^ August 7-10, 1910.
Charles. S. Minot (Chairman), Franklin P. Mall, James Playfair McMurrich,
George A. Piersol, Greorge S. Huntington, G. Carl Huber (Secretary).
American Members of the IntemcUional Committee on Reformation of the Myological
Nomenclature
James Platfair McMurrich, Ross G. Harrison
Delegate to the Council of the American Association for the Advancement of Science
Simon H. Gage
Members of Smithsonian Committee on the Table at Naples
George S. Huntington
Honorary Members
S. Ramon y Cajal Madrid, Spain
John Cleland Glasgow, Scotland
John Daniel Cunningham Edinburgh, Scotlarui
Camillo Golgi Pavia, Italy
Oscar Hertwig Berlin, Germany
Alexander Macallister Cambridge, England
A. Nicholas Paris, France
L. Ranvier Paris, France
Gustav Retzius Stockholm, Sweden
Carl Toldt •. Vienna, Austria
Sir William Turner Edinburgh, Scotland
WiLHELM Waldbybr Berlin, Germany
{| class="wikitable mw-collapsible mw-collapsed"
! American Association Of Anatomists - Members (1910)  
|-
| Addison, William Henry Fitzgerald, B.A., M.B., Demonstrator of Histology and Embryology, University of Pennsylvania, S9B8 Pine Street, Philadelphia, Pa.
Allen, Bennet Mills, Ph.D., Instructor in Anatomy, University of Wisconsin, 710 Nouhlin Place, Madison, Wis.
Allen, William F., A.M., Collector and Assistant, Marine Laboratory, University of California, New Monterey, Calif.
Allis, Edward Phelps, Jr., LL.D., Palais de CarnoUs, Menione, France.
Allison, Nathaniel, M.D., Instructor in Orthopedic Surgery, Washington University, Ldnmar Building, St. Louis, Mo.
Baker, Frank, A.M., M.D., Ph.D. (Vice-Pres. '88-'91, Pres. '96-'97), Professor of Anatomy, University of Georgetown, 1788 Columbia Road, Washington, D.C.
Baldwin, Wesley Manning, Instructor in Anatomy, Cornell University Medical School, First Avenue and 28th Street, New York City, N. Y.
Bardeen, Charles Russell A.B., M.D. (Ex. Com. *06-'09.) Professor of Anatomy, University of Wisconsin, Science Hall, Madison, Wis.
Barker, Lewellys Franklin, M.D., (Ex. Com. '02-'05), Professor of Medicine, Johns Hopkins University, 10S5 North Calvert Street, Baltimore, Md.
Bates, George Andrew, M.S., Professor of Histology, Tufts College, J^IS Huntington Avenue, Boston, Mass.
Baumgartner, William J., A.M. Assistant Professor of Histology and Zoology, University of Kansas, Lawrence, Kas.
Bean, Robert Bennett, B.S., M.D., Professor of Anatomy, Medical School, Manila, P.I.
Bell, Elexious Thompson, B.S., M.D., Assistant Professor of Anatomy, University of Missouri, Columbia Club, Columbia, Mo.
Benbley, Benjamin Arthur, Ph.D., Associate Professor of Zodlogy, University of Toronto, 816 Brunswick Avenue, Toronto, Can.
Bensley, Robert Russell, A.B., M.D. (Second Vice-Pres. '06-'07, Ex. Com. '08'12). Professor of Anatomy, University of Chicago, Chicago, III.
Bevan, Arthur Dean, M.D. (Ex. Com. '96-'98), Professor of Surgery, University of Chicago, 100 State Street, Chicago, III.
BiGELOW, Robert P., Ph.D., Instructor in Biology, Massachusetts Institute of Technology, 4^1 Boylston Street, Boston, Mass.
Blair, Vilray Papin, A.M., M.D., Lecturer on Descriptive Anatomy, Washington
University, S7B9 Delmar Boulevard, St. Louis, Mo.
Blake, Joseph Augustus, A.B. M.D., Professor of Surgery, Columbia Uniyersity, 601 Madison Avenue, New York City, N.Y.
Bloodgood, Joseph C, A.B., M.D., Associate Professor of Surgery, Johns Hopkins University, 904 N. Charles Street, Baltimore, Md.
Bremer, John Lewis, M.D., Harvard Medical School, 4^6 Beacon Street, Boston, Mass.
Brickner, Samuel Max, A.M., M.D., Gynecologist to Mt. Sinai Hospital Dispensary, 136 W. 86th. Street i New York City.
Br5del, Max, Associate Professor of Art as Applied to Medicine, Johns Hopkins University, Baltimore, Md.
Brooks, William Allen, M.D., 167 Beacon Street j BostoUy Mass.
Browning, Wiluam, Ph.D., M.D., Professor of Diseases of the Mind and Nervous System, Long Island College Hospital, 54 Lefferts Place, Brooklyn, N. Y.
Bruner, Henry Lane, Ph.D., Professor of Biology, Butler College, S50 South Ritter Avenue, Indianapolis, Ind.
Bunting, Charles Henry, B.S., M.D., Professor of Pathology, University of Wisconsin, Madison, Wis.
Burrows, Montrose I., M.D., Fellow, Rockefeller Institute, 66th Street and Avenue A, New York City, N. Y.
Campbell, William Francis, A.B., M.D., Professor of Anatomy and Histology, Long Island College Hospital, S94 Clinton Avenue, Brooklyn, N. Y.
Carpenter, Frederick Walton, Ph.D.,. Instructor in Zodlogy, University of Illinois, 1008 West Orange Street, Urbana, III.
Carr, William Phillips, M.D., Professor of Physiology, Medical Department, Columbia University, I4I8 L Street, N.W., Washington, B.C.
Chamberlain, Ralph V., Ph.D., Professor of Zodlogy, University of Utah, Salt Lake City, Utah.
Cheever, David, A.B., M.D., Demonstrator of Anatomy, Harvard Medical School, 20 Hereford Street, Boston, Mass.
Child, Charles Manning, Ph.D., Assistant Professor of Zoology, University of Chicago, Chicago, III.
Clapp, Cornelia Maria, Ph.D., Professor of Zodlogy, Mount Holyoke College, SoiUh Hadley, Mass.
Clark, Elbert, B.S., Assistant in Anatomy, University of Chicago, Chicago, III.
Clark, Eliot R., M.D., Instructor in Anatomy, Johns Hopkins University, Baltimore, Md.
CooHiLL, George E., Ph.D., Professor of Zoology, Denison University, Granville, Ohio.
CoHOE, Benson A., A.B., M.D., Professor of Anatomy, University of Pittsburg, 706 North Highland Avenue, Pittsburg, Ohio.
CoNANT, Wiluam Merritt, M.D., Instructor in Anatomy in Harvard Medical School, 4^6 Commonwealth Avenue, Boston, Mass.
CoNKUN, Edwin Grant, A.M., Ph.D., Sc.D., Professor of Zodlogy, Princeton University, Princeton, N. J.
Corning, H. M., M.D., Professor and Prosector of Anatomy, Basel, Switzerland.
Corson, Eugene Rollins, B.S., M.D., // Jones Street, East Savannah, Ga.
Craig, Joseph Davis, A.M. M.D., Professor of Anatomy, Albany Medical College, 12 Ten Broeck Street, Albany, N. Y.
CuLLEN, Thomas S., M.B., Associate Professor of Gynecology, Johns Hopkins University, S West Preston Street, Baltimore, Md.
Dahlgren, Ulric, M. S., Assistant Professor of Biology, Princeton University, 7 Evelyn Place, Princeton, N. J.
Dandy, Walter E., A.B., Johns Hopkins Med'cal School, Baltimore, Md.
Darrach, William, A.M., M.D., Demonstrator of Anatomy, Columbia University, 61 West 48th Street, New York City, N. Y.
Davidson, Alvin, M.A., Ph.D., Professor of Biology, Lafayette College, Easton, Pa.
Davis, David M., B.S., Johns Hopkins Medical School, Baltimore, Md,
Dawburn, Robert H. Mackay, M.D., Professor of Anatomy, New York Polyclinic Medical School and Hospital, 106 West 74th Streety New York City, N. Y,
Dean, Bashford, Ph.D., Professor of Vertebrate Zodlogy, Columbia University, £0 W. 82nd Street, New York City, N. Y.
Dbwitt, Lydia M., M.D., B.S., Instructor in Histology, University of Michigan, Ann Arbor, Michigan.
Dexter, Franklin, M.D., IJtS Marlborough Street, Boston, Mass.
Dixon, A. Francis, M.B., Sc. D., University Professor of Anatomy, Trinity College, 7S Grosvener Road, Dublin, Ireland.
Dodson, John Milton, A.M., M.D., Professor of Medicine, University of Chicago, 5806 Washington Boulevard, Chicago, III.
Donaldson, Henry Herbert, Ph.D., Sc.D. (Ex. Com. '09-' 13), Professor of Neurology, The Wistar Institute of Anatomy, Philadelphia, Pa.
Dunn, Elizabeth Hopkins, A.M., M.D., Associate in Anatomy, University of Chicago, Chicago, III.
DwiGHT, Thomas, M.D., LL.D. ( Ex. Com. '91-'93, Pres. '94-'95), Parkman Professor of Anatomy, Harvard Medical School, Boston, Mass.
EccLBS, Robert G., M.D., Professor Organic Chemistry, Brooklyn College of Pharmacy, 191 Dean Street, Brooklyn, N. Y.
Edwards, Charles Lincoln, Ph.D., Professor of Natural History, Trinity College, 89 BiLckingham Street, Hartford, Conn.
Eigenmann, Carl H., Ph.D., Professor of Zoology, Indiana University, Bloomington, Ind.
Eluot, Gilbert M., A.M., M.D., Assistant Demonstrator of Anatomy, Medical School of Maine, 152 Maine Street, Brunswick, Me.
Emmel, Victor E., Ph.D., Instructor in Embryology and Histology, Washington University, St. Louis, Mo.
Erdman, Charles Andrew, M.D., Professor of Anatomy, Medical Department, University of Minnesota, Minneapolis, Minn.
EssiCK, Charles Rhein, B.A., M.D., Assistant in Anatomy, Johns Hopkins University, Baltimore, Md.
Etherington, Frederick, M.D., Professor of Anatomy, Queen's University, 218 Albert Street, Kingston, Canada.
Evans, Herbert McLean, B.S., M. D., Instructor in Anatomy, Johns Hopkins University, Baltimore, Md.
Eycleshymer, Albert Chauncy, B.S., Ph.D., Professor of Anatomy, University of St. Louis, St. Louis, Mo.
Ferguson, Jeremiah Sweetser, M.Sc, M.D., Instructor in Histology, Cornell University Medical College, 55 W. 28th Street, New York City, N. Y.
Ferris, Harry Burr, A.B., M.D., Professor of Anatomy, Medical Department, Yale University, S95 St. Ronan, New Haven, Conn.
Fischelis, Philip, M.D., Associate Professor of Histology and Embryology, Medico-Chirurgical College, 828 N. 6th Street, Philadelphia, Pa.
FuNT, Joseph Marshall, B.S., A.M., M.D. (Second Vice-Pres. '03-'04.) Professor of Surgery, Yale University, Sll Temple Street, New Haven, Conn.
Fox, Henry, Ph.D., Professor of Biology, Ursinus College, Collegeville, Pa.
Frost, Gilman Dubois, A.M., M.D., Professor of Anatomy, Dartmouth Medical School, Hanover, N. H.
Gage, Simon Henry, B.S., (Ex. Com. '06-'ll), Emeritus Professor of Histology and Embryology, Cornell University, Ithaca^ N, F.
Gage, Mrs. Susanna Phelps, B.Ph., 4 South Aventief Ithaca, N, Y,
Gallaudet, Bern Btjdd, A.M., M.D., Demonstrator of Anatomy, Colimibia University, The Stuyvesant, 17 Livingston Place, New York City, iV. Y,
Gehring, Norman J., A.B., M.D., 706 N. Robinson Street, Oklahoma City, Oklahoma.
Gbrrish, Frederick Henby, A.M., M.D., LL.D. (Ex. Com. '93-'95, '97-'99, '02-'06, Vice Pres. '00-* 01), Professor of Surgery, Bowdoin College, 675 Congress Street, Portland, Me.
Gibson, James A., M.D. Professor of Anatomy, University of Buffalo, 170 Mariner Street, Buffalo, N. Y.
GiLMAN, Philip Kingsworth, B.A., M.D., Assistant in Operative Surgery, Medical School, Manila, P. I.
GoETTSCH, Emil, Ph.D., M.D., Assistant in Surgery, Johns Hopkins University, Baltimore, Md.
Greenman, Milton J., Ph.B., M.D., Director of the Wistar Institute of Anatomy, S6th Street and Woodland Avenue, Philadelphia, Pa.
GuYER, Michael F., Ph.D., Professor of Zoology, University of Cincinnati, 56i Evanswood, Clifton, Cincinnati, Ohio.
Halstead, William Stewart, M.D., Professor of Surgery, Johns Hopkins University, 1201 Eutaw Place, Baltimore, Md.
Hamann, Carl A., M.D. (Ex. Com. '02-'04), Professor of Anatomy, Medical Department, Western Reserve University, 40J^ Osborn Building, Cleveland, Ohio.
Hardesty, Irving, A.B., Ph.D., Professor of Anatomy, Tulane University, New Orleans, La.
Hare, Earl R., A.B., M.D., Instructor in Anatomy, University of Minnesota, SIS7 14th Avenue, Minneapolis, Minn.
Harper, Eugene Howard, Ph.D., Instructor in Zoology, Northwestern University, 1105 Grant Street, Evanston, III.
Harrison, Ross Granville, Ph.D., M.D., Professor of Comparative Anatomy, Yale University, 2 Hillhouse Avenue, New Haven, Conn.
Harvey, Basil Coleman Hyatt, A.B., M.B., Instructor in Anatomy, University of Chicago, ^4 E. 60th Street, Chicago, III.
Hatai, Shinkishi, Ph.D., Associate in Neurology, Wistar Institute of Anatomy, Philadelphia, Pa.
Hathaway Joseph H., A.M., M.D., Professor of Anatomy, University of Louisville, Louisville, Ky.
Haynes, Irving Samuel, Ph.B., M.D., Professor of Practical Anatomy, Cornell University Medical College, 107 W. 85th Street, New York City, N. Y.
Hazen, Charles Morse, A.M., ^1.D., Professor of Physiology, Medical College of Virginia, Richmond, Bon Air, Va.
Heisler, John C, M.D., Professor of Anatomy, Medico-Chirurgical College, Philadelphia, Pa., S829 Walnut Street, Philadelphia, Pa.
Herrick, Charles Judson, Ph.D., Professor of Neurology, University of Chicago, Chicago, III.
Hbrtzler, Arthur E., A.M., M.D., Ph.D., Professor of General and Surgical
Pathology and Experimental Sur^e-y, University Medical College, 402 Argyle
Building f Kansas Cityy Mo, Heuer, George Julius, B.S., M.D., Assistant Resident-Surgeon, Johns Hopkins
Hospital, Baltimore^ Md. Hewson, Addinell, A.m., M.D., Professor of Anatomy of Philadelphia Polyclinic for Graduates of Medicine ; Secretary of Pennsylvania State Anatomical
Board, 21f^ Spruce Street, Philadelphiay Pa, Hill, Eben Clayton, A.B., M.D., First Lieutenant, Medical Reserve Corps, U. S.
A., Washington, D, C. Hill, Howard, M.D., Professor of Anatomy, University Medical College, 4$6
Argyle Building, Kansas City, Mo. Hilton, William A., Ph.D., Instructor in Histology, Cornell University, Ithaca,
N. Y. Hodge, C. F., Ph.D., Professor of Biology, Clark University, Worcester, Mass. Hoeve, Heikobus, J. H. M.D., Professor of Anatomy, Drake University, Des
Moines, Iowa. Hooker, Davenport, M.A., Instructor in Anatomy, Medical Department, Yale
University, 1S3 Canner Street, New Haven, Conn. Hopkins, Grant Sherman, Sc.D., D.V.M., Professor of Veterinary Anatomy,
Cornell University, 125 Dry den Road, Ithaca, N. Y. Howard, Wm. T., M.D., Professor of Pathology, Western Reserve University,
Cleveland, Ohio. Hrdlikca, Ales, M.D., Curator of the Division of Physical Anthropology, United
States National Museum, Washington, D. C. HuBER, G. Carl, M.D. (Second Vice-Pres. '00— '01, Secretary-Treasurer '02-' 13).
Professor of Histology and Embryology, University of Michigan, 13S0 Hill
Street, Ann Arbor, Mich. Huntington, George S., A.M., M.D., D.Sc, LL.D. (Ex. Com. '95-'97, '04-'07,
Pres. '99-'03), Professor of Anatomy, Columbia University, 4S7 W. 69th • Street, New York City, N. Y. Ingalls, N. William, M.D., Instructor in Anatomy, Medical College, Western
Reserve University, St. Clair Avenue and East 9th Street, Cleveland, Ohio. Jackson, Clarence M., M.S., M.D., Professor of Anatomy and Histology, University of Missouri, 811 College Avenue, Coluanbia, Mo. Jayne, Horace, M.D., Ph.D., Walling ford. Pa. Johnson, Franklin P., A.B., Austin Teaching Fellow, Harvard Medical School,
Boston, Mass. Johnston, John B., Ph.D., Professor of Comparative Neurology, University of
Minnesota, Minneapolis, Minn. Jordan, Harvey Ernest, Ph.D., Adjunct Professor of Anatomy, University of
Virginia, Charlottesville, Va. •
Keiller, William, L.R.C.P. and F.R.C.S.Ed. (Second Vice-Pres. '98-'99.) Professor of Anatomy, University of Texas, Galveston, Tex. Kelly, Howard Atwood, A.B., M.D., LL.D., Professor of Gynecology, Johns
Hopkins University, I4I8 Eutaw Place, Baltimore, Md. Kemp, George T., M. D.,Ph.D., Hotel Beardsley, Champaign, III, Kerr, Abram T., B.S., M.D., Professor of Anatomy, Cornell University, Ithaca, N.Y.
Kingsbury, Benjamin F., Ph.D., M.D., Professor of Histology and Embryology, Cornell University, Ithaca, N. Y.
KiNOSLET, J. S., Sc.D., Professor of Biology, Tufts College, Mass.
Kirk, Edwin Garvey, B.S., Associate Instructor in Anatomy, University of Chicago, 6S7 Jackson Boulevard, Chicago, III.
Knower, Henry McE, A.B., Ph.D., ^Lecturer in Anatomy, Toronto University, Toronto, Canada.
KoFOiD, Charles Atwood, Ph.D., Professor of Histology and Embryology, University of California, Berkeley, Cal.
Kutchin, Harriet Lehmann, A.M., Assistant in Biology, University of Montana, Missoula, Mont.
Kyes, Preston, A.M., M.D., Assistant Professor of Experimental Pathology, University of Chicago, Quadrangle Club, Chicago, III.
Lamb, Daniel Smith, A.M., M.D. (Secretary -Treasurer '90-'01, Vice-Pres. '02'03.) Pathologist Army Medical Museum, Professor of Anatomy, Howard University, Medical Department, £114 l^lh Street, N.W., Washington, D. C.
Lambert, Adrian V. S., A.B., M.D., Instructor in Surgery, Columbia University, 29 W. Seth Street, New York City, N. Y.
Land acre, Francis Leroy, A.B., Associate Professor of Zo5logy, Ohio State University, Columbus, Ohio.
Lane, Michael Andrew, B.S., Assistant in Histology and Embryology, University of Chicago, lSi6 Jackson Boulevard, Chicago, III.
LeCron, Wilbur L., A.B., M.D., Hartford Hospital, Hartford, Conn.
Leb, Thomas G., B.S., M.D., (Ex. Com. '08-'10.) Professor of Anatomy and Director of the Department of Anatomy, University of Minnesota, Minneapolis, Minn.
LeFevre, George, Ph.D. Professor of Zoology, University of Missouri, Columbia, Mo.
Leidy, Joseph Jr., A.M., M.D. 1319 Locust Street, Philadelphia, Pa.
Lempe, George Gustave, A.B., M.D., Lecturer on Anatomy, Albany Medical College, 4£ Eagle Street, Albany, N. Y.
Lewis, Dean D., M.D., Assistant Professor of Surgery, Rush Medical College, 100 State Street, Chicago, III.
Lewis, Frederick T., A.M., M.D., Assistant Professor of Embryology, Harvard Medical School, Boston, Mass.
Lewis, Warren Harmon, B.S., M.D., Associate Professor of Anatomy, Johns Hopkins University, Baltimore, Md.
Lewis, William Evan, M.D., Professor of Anatomy, Miami Medical College, 409 E. 6th Street, Cincinnati, Ohio.
LiLLiE Frank Rathay, Ph.D., Professor of ZoSlogy and Embryology, University of Chicago, Chicago, III.
LissER, Hans, Johns Hopkins Medical School, Baltimore, Md.
LocY, WiLUAM A., Ph.D., Sc.D., Professor of Zoology and Director of the Zodlogical Laboratory, Northwestern University, Evanston, III.
LoEB, Hanau Wolf, A.M., M.D., Professor of Nose and Throat Diseases, St. Louis University, 6S7 N. Grand Avenue, St. Louis, Mo.
LoEB, Leo, M.D., Assistant Professor of Experimental Pathology, University of Pennsylvania, Philadelphia, Pa.
McCarthy, John George, M.D., Lecturer on Anatomy, McGill University, 61 Drummond Sireety Montreal^ Canada,
McClellan, George, M.D., Prof essor of Applied Anatomy, Jefferson Medical College, 1116 Spruce Street^ Philadelphia^ Pa,
McClendon, J. F., Ph.D., Assistant in Histology, Cornell University Medical School, New York City, N, Y,
McClurb, Charles Freeman Williams, A.M., Ph.D., Sc.D., Professor of Comparative Anatomy, Princeton University, Princeton, N. J,
McDonald, Archibald L., A.B., M.D., Professor of Anatomy and Physiology, University of North Dakota, Grand Forks, iV. Dak.
McDoNouGH, Edward Joseph, A.B., M.D., Instructor in Histology, Medical School of Maine, 624 Congress Street, Portland, Me,
McGiLL, Caroline, A.M. Ph.D., Instructor in Anatomy, University of Missouri, Columbia, Mo,
McMurrich, James Playfair, A M., Ph.D. (Ex. Com. '06- W, Pres '08-'09), Professor of Anatomy, University of Toronto, Toronto, Caruida,
McNeal, Ward J., Ph.D., M.D., Assistant Professor of Bacteriology, University of Illinois, 1005 W. Oregon Street, Urbana, III.
Major, Ralph Hermann, A.B., Johns Hopkins Medical School, Baltimore, Md.
Mall, Franklin P., A.M., M.D., LL.D., D.Sc. (Ex. Com. '00-'05, Pres. '06-W), Professor of Anatomy, Johns Hopkins University, Baltimore, Md,
Mann, Gustavb, M.D., B.Sc., Professor of Physiology, Tulane University, New Orleans, La.
Mark, Edward Laurens, Ph.D., LL.D., Hersey Professor of Anatomy and Director of the Zoological Laboratory, Harvard University, 109 Irving Street, Cambridge, Mass.
Martin, Walton, Ph.D., M.D., Instructor in Surgery, Columbia University, 68 E, 56th Street, New York City, N,Y.
Matas, Rudolph, M.D., Professor of Surgery, Tulane University, S255 St. Charles Avenue, New Orleans, La,
Mellus, Edward Lindon, M.D., Anatomical Laboratory, Johns Hopkins University Medical School, Baltimore, Md.
Mercer, William F., Ph.D., Professor of Biology, Ohio University, iSOO E. State, Street, Athens, Ohio.
Meyer, Adolf, M.D., LL.D., Professor of Psychiatry, Johns Hopkins University Baltimore, Md.
Meyer, Arthur W., S.B., M.D., Professor of Anatomy, Leland Stanford University, Palo Alto, Calif.
Miller, Adam M., A.M., Instructor in Anatomy, Columbia University, New York City, N. Y.
Miller, Walter McNat., B.Sc, M.D., Professor of Pathology and Bacteriology, University of Missouri, Columbia, Mo.
Miller, William Snow, M,.D. (Vice-Pres. '08-'09), Associate Professor of Anatomy, University of Wisconsin, University Club, Madison, Wis.
Minot, Charles Sedgwick, S.B., (Chem), S.D., LL.D., D.Sc. (Ex. Com. '9^'02, '06-'08, Pres. '04-'05), Professor of Comparative Anatomy, Harvard Medical School, Boston, Mass,
MiXTEB, Samuel Jason, B.S., M.D., Instructor of Surgery, Harvard Medical School, 180 Marlborough Streety Boston^ Mass.
Moody, Mart Blair, M.D., 166 S. Marengo Avenue, Pasadena, Cal.
Moody, Robert Orten, B.S., M.D., Assistant Professor of Anatomy, University of California, Berkeley, Cal.
Morgan, James Dudley, A.B., M.D., Clinical Professor, Georgetown University, 919 15th Street, McPherson Square, Washington, D. C.
Morgan, Thomas H., Ph.D., Professor of Experimental Morphology, Columbia University, New York City, N. Y.
Morse, Max, Ph.D., Instructor in Biology, College of the City of New York, New York City, N. Y.
MuNROB, John Cummings, A.B., M.D., Surgeon in Chief, Carney Hospital, 17S Beacon Street, Boston, Mass.
MuNsoN, John P., Ph.D., Head of the Department of Biology, Washington State Normal School, Ellensburg, Washington.
Murphy, James B., B.S., Pathological Institute, Wards Island, New York City, N. Y.
Myers, Burton D., A.M., M.D., Professor of Anatomy, Indiana University, Bloomington, Ind.
Nachtrieb, Henry Francis, B.S., Professor of Animal Biology, University of Minnesota^ 905 S.E. 6th Street, Minneapolis, Minn.
Nbal, Herbert Vincent, Ph.D., Professor of Biology, Knox College, 750 N. Academy Street, Galeshurg, III.
Noble, Harriet Isabel, M.D., Demonstrator of Anatomy, Woman's Medical College of Pennsylvania, Noble, Pa.
Parker, Charles Aubrey, M.D., Instructor in Anatomy, University of Chicago, 100 State Street, Chicago, III.
Parker, George Howard, D. Sc, Professor of Zodlogy, Harvard University, 16 Berkeley Street, Cambridge, Mass.
Paton, Stewart, A.B., M.D., Princeton University, Princeton, N. J.
Patten, Wiluam, Ph.D., Professor of Zodlogy, Dartmouth College, Hanover, N.H*
Patterson, James. B.S., Assistant in Anatomy, University of Chicago, Chicago, III.
PiBRSOL, George A., M.D., Sc.D., (Vice-Pres. '98-'99, '93-'94, '06-W.) Professor of Anatomy, University of Pennsylvania 47H Chester Avenue, Philadelphia, Pa.
PoHLMAN, August G., M.D., Junior Professor of Anatomy, Indiana University, 411 Fess Avenue, Bloomington, Ind.
Potter, Peter, M.S., M.D., 51 Owsley Block, Butte, Montana.
Prentiss, H. J., M.D., M.E. Professor of Anatomy, University of Iowa, Iowa City, la.
Primrose, Alexander, M.B., C.M.Ed., M.R.C.S.Eng., Professor of Surgery, University of Toronto, 100 College Street, Toronto, Canada.
Pryor, Joseph Wiluam, M.D., Professor of Anatomy and Physiology, State College of Kentucky, 261 N. Broadway, Lexington, Ky.
Radasch, Henry E., M.S. M.D., Associate in Histology and Embryology, Jefferson Medical College, 914 S. 47th Street, Philadelphia, Pa.
Ranson, Stephen W., M.D., Ph.D., Assistant Professor of Anatomy, Northwestern University Medical School, Chicago^ III.
Reese, Albert Moore, A.B., Ph.D., Professor of Zodlogy, West Virginia University', MorgantotDTij W. Va.
Reford, Lewis L., A.B., M.D. Assistant Resident Surgeon, Johns Hopkins Hospital, Baltimore^ Md.
Retzer, Robert, M.D., Assistant Professor of Anatomy, University of Minnesota, Minneapolis^ Minn.
Revell, Daniel Graisberry, A.B., M.B., Department of Public Health, Edmon" ton, Alberta, Canada.
Rice, Edward Loramus, Ph.D., Professor of Zoology, Ohio Wesley an University, 1S4 W. Lincoln Avenue, Delaware, Ohio.
Russell, Nelson G., M.D., Assistant in Anatomy, University of Buffalo, 476 •Franklin Street, Buffalo, N. Y.
Sarin, Florence R., B.S., M.D. (Second Vice-Pres. '08-'09), Associate Professor of Anatomy, Johns Hopkins University, Baltimore, Md.
Sachs, Ernest, A.B., M.D., Surgeon, 1070 Madison Avenue, New York City, N". Y.
Sampson, John Albertson, A.B., M.D., 180 Washington Avenue, Albany N". Y.
Santee, Harris E., Ph.D., M.D., Professor of Anatomy, University of Illinois, 2819 Warren Avenue, Chicago, III.
ScANNON, Richard E., A.B., Instructor in Histology and Embryology, Harvard Medical School, Boston, Mass.
Schaeffer, Jacob P., A.B., M.E., M.D., Instructor in Anatomy, Cornell University, Ithaca, N. Y.
Schaeffer, Marie Charlotte,M.D., Lecturer on Biology and Normal Histology, University of Texas, Galveston, Texas.
Schoemaker, Daniel M., B.S., M.D., Associate Professor of Anatomy, St. Louis University, St. Louis, Mo.
ScHULTE, Hermann Von W., A.B., M.D., Adjunct Professor of Anatomy, Columbia University, 176 W. 87th Street, New York City, N. Y.
ScHMiTTER, Ferdinand, A.B., M.D., First Lieutenant, Assistant Surgeon, U. S. Army, Fort Slocum, New York.
Seelio, Major G., A.B., M.D., Assistant in Anatomy, St. Louis University, 5S7 N. Grand Avenue, St. Louis, Mo.
Selling, Lawrence, A.B., Johns Hopkins Medical School, Baltimore, Md.
Senior, Harold D., M.B., F.R.C.S., Professor of Anatomy, Syracuse University, Orange Street, Syracuse, N. Y.
Shambaugh, George E., Ph.B. M.D., Instructor in the Anatomy of the Ear, Nose and Throat, University of Chicago, 100 State Street, Chicago, III.
Sheldon, Ralph Edward, A.M., M.S., Assistant Professor of Anatomy, University of Pittsburg, Brereton Avenue and 30th Street, Pittsburg, Pa.
Shepherd, Francis John, M.D., CM., M.R.C.S., Eng., LL.D. (Second Vice-Pres. '94-^97, Ex. Com. '97-'02.) Professor, of Anatomy, McGill University, 16ii Mansfield Street, Montreal, Canada.
Silvester, Charles Frederick, Assistant in Anatomy, Princeton University, 10 Nassau Hall, Princeton, N. J.
SissoN, Septimus, B.S., V.S. Professor of Comparative Anatomy, Ohio State University, Columbus, Ohio.
Sluder, Greenfield, M.D., S64ii Washington Avenue, St. Louis, Mo,
Smith, Charles Dbnnison, A.M., M.D., Professor of Physiology, Medical School of Maine, Maine General Hospital, Portland, Me.
Smith, Eugene Alfred, M.D., 1018 Maine Street, Buffalo, N. Y.
Smith, Frank, A.M., Associate Professor of Zoology, University of Illinois, 91S W. California Avenue, Urbana, III.
Smith, Helen Williston, A.B., Johns Hopkins Medical School, Baltimore, Md.
Smith, J. Holmes, M.D., Professor of Anatomy, University of Maryland, B206 St. Paul Street, Baltimore, Md.
Spitzka, Edward Anthony, M.D., Professor of General Anatomy, JefiFerson Medical College, 10th and Walnut Streets, Philcidelphia, Pa.
Starks, Edwin Chapin, Assistant Professor of Zoology, Leland Stanford University, Palo Alto, Cal.
Steensland, Halbert Severin, B.S., M.D., Associate Professor of Pathology and Bacteriology, and Director of the Pathological Laboratory, Syracuse University, 506 University Place, Syracuse, N. Y.
Stiles, Henry Wilson, M.D., Assistant Professor of Anatomy, Tulane University, New Orleans, La.
Stockard, Charles Rupert, Ph.D., Assistant Professor of Experimental Morphology, Cornell University Medical School, New York City, N. Y,
Stotzenburg, James M., M.D., Curator and Junior Associate in Anatomy, Wistar Institute of Anatomy, Philadelphia, Pa.
Streeter, George L., A.M., M.D., Prof essor of Anatomy , University of Michigan, Ann Arbor, Mich.
Stromsten, Frank Albert, D.Sc, Instructor in Animal Biology, University of Iowa, 2J^ East Burlington Street, Iowa City, la.
Strong, Oliver S., Ph.D., Instructor in Histology and Embryology, Columbia University, 4S7 W. 69th Street, New York City, N. Y.
Strong, Reuben Myron, Ph.D., Instructor in Zodlogy, University of Chicago, Chicago, III.
Sudler, Mervin T., M.D., Ph.D., Professor of Anatomy, University of Kansas, 1037 Tennessee Street, Lawrence, Kan.
Sundwall, John, Ph.D., Professor of Anatomy, University of Utah, Salt Lake City, Utah.
Taussig, Frederick Joseph, A.B., M.D., Clinical Assistant in Gynecology, Washington University, Metropolitan Building, St. Louis, Mo.
Taylor, Edward W., A.M., M.D., Instructor in Neurology, Harvard Medical School, 467 Marlborough Street, Boston, Ma.ss.
Taylor, Ewing, A.B., M.D., 19 Arden Place, Yonkers, N. Y.
Terry, Robert James, A.B., M.D., Professor of Anatomy, Washington University, 1806 Locust Street, St. Louis, Mo.
Thro, William C, A.M., iS9 W. 160 Street, New York City, N. Y.
Thyng, Frederick Wilbur, Ph.D., Assistant Professor of Anatomy, Northwestern University Medical School, Chicago, III.
Tilney, Frederick, A.B., M.D., Associate in Anatomy, Columbia University, 161 Henry Street, Brooklyn, N. Y.
Tobie, Walter E., M.D., Professor of Anatomy. Medical School of Maine, B Deering Street, Portland, Me,
TuppER, Paul Yoer, M.D., Professor of Applied Anatomy, Washington University, Ldnmar Building^ St. Louis, Mo.
TucKERMAN, FREDERICK, M.D., Ph.D., Amherst, Mass.
Waite, Frederick Clayton, A.M., Ph.D., Professor of Histology and Embryology, Western Reserve University, E. 9th Street and St. Clair Avenue, Cleveland, Ohio.
Walker, George, M.D., Instructor in Surgery, Johns Hopkins University, Cor, Charles and Centre Streets, Baltimore, Md,
Ward, Charles Howard,557 West Aventie, Rochester, N. Y,
Warren, John, M.D., Assistant Professor of Anatomy, Harvard Medical School, Boston, Mass.
Webster, John Clarence, B.A., M.D., F.R.C.P.Ed., Professor of Obstetrics and Gynecology, University of Chicago, 706 Reliance Building, Chicago, III.
Weed, Lewis Hill, A.M., Johns Hopkins Medical School, Baltimore, Md.
Weidenreich Franz, M.D., a.o. Professor and Prosector of Anatomy, 19 Vogesen Street, Strassburg, i. Els. Germany.
Wbisse, Faneuil D., M.D., (Second Vice-Pres. '88-'89.), Professor of Anatomy, New York College of Dentistry, 19 Gramercy Park, New York City, N. Y.
West, Charles Ignatius, M.D., Lecturer on Topographical Anatomy, Howard University, 9B4 M Street N.W., Washington, D. C.
Wbysse, Arthur Wissland, A.M., M.D., Ph.D., Professor of Biology, Boston University, 688 Boylston Street, Boston, Mass.
Whitehead, Richard Henry, A.B. M.D. Professor of Anatomy, University of Virginia, Charlottesville, Va.
Wilder, Burt G., M.D., B.S. (Ex. Com. '90-'92, Vice-Pres. *93-'97, Pres. '98-'99), Professor of Neurology, Vertebrate Zoology and Physiology, Cornell University, Ithaca, N. Y.
Wilder, Harris Hawthorne, Ph.D., Professor of Zodlogy, Smith College, 72 Aryads Green, Northampton, Mass.
Williams, Leonard Worcester, Ph.D., Instructor in Comparative Anatomy, Harvard Medical School, Boston, Mass.
Williams, Stephen Riggs, Ph.D., Professor of Biology and Geology, Miami University, Box 150, Oxford, Ohio.
Wilson, J. Gordon, M.A. M.B., CM. (Edin), M.D., Professor of Otology, Northwestern University Medical School, Chicago, III.
Wilson, James Meredith, Ph.D., M.D., Assistant Professor of Histology and Embryology, St. Louis University, St. Louis, Mo.
WiNSLOw, Guy Monroe, Ph.D., Instructor in Histology, Tufts Medical College, lJt6 Woodland Road, Auburndale, Mass.
WiTHERSPOON, Thomas Casey, M.D., S07 Granite Street, Butte, Montana.
Wolcott, Robert Henry, A.M., M.D., Professor of Anatomy, University of Nebraska, Station A, Lincoln, Neb.
Woods, Frederick Adams, M.D., Lecturer in Biology, Massachusetts Institute of Technology 1006 Beacon Street, Brookline, Mass.
WooLBEY, George, A.B., M.D., Professor of Anatomy and Clinical Surgery, Cornell University Medical College, 117 E. 36th Street, New York City, N. Y.

Latest revision as of 19:43, 25 February 2020

The Phylogenetic Relations Of The Lymphatic And Blood Vascular Systems In Vertebrates

Huntington GS. The phylogenetic relations of the lymphatic and bloodvascular systems in vertebrates. (1910) Anat. Rec. 4(1): 1-14.

GEO. S. HUNTINGTON

From the Anatomical Laboratory of Columbia University

At a time when the ontogenesis of the vertebrate, and especially of the mammalian, lymphatic system has called forth general interest and considerable activity in research, it seems advisable to regard the mutual relations of the haemal and lymphatic divisions of the vertebrate vascular system from the standpoint of their phylogeny, in as far as material for such observations is to date available, and in turn to fit the facts ascertained by the study of manmialian lymphatic ontogenesis into the framework obtained by these generalized comparisons.

This appears all the more advisable when we consider that any valid theory of lymphatic development must, on the one hand, agree in its postulates with the phylogenetic facts, as far as they are definitely established, and that, on the other hand, a review of the ascertained comparative conditions of the two systems in their mutual bearing on the general question will serve to direct attention to the problems of vascular morphology as yet imperfectly known, and thus guide the inquiries in the right direction.

In the earliest zoological conditions in multicellular organisms a simple circulation suflSces to supply all the metabolic demands of the tissues. Such a circulation is attained when a sjrstem of intercellular canals develops in which a clear plasmatic fluid, without free cellular elements moves in response to the pulsations of contractile areas included within the system.

In generd terms a circulation of this kind is, from the phylogenetic standpoint, a primary formation and represents the primitive lymphatic type of vascular organization, from which in higher forms the haemal system develops as a secondary vascular acquisition. In the physiological sense this establishment of a haemal circulation, as a graft on the earlier circulation of noncellular plasma, is to be interpreted as the expression of the increased rate of tissue combustion and the resulting growing demands of the organism for oxygen, required in the ascent to higher animal types. The biochemical agent which makes this elevation from the lower to the next higher rung of the zoological ladder possible, is the haemoglobin, and the morphological expression of its employment is found in the genesis of the modified mesodermal cell entering the circulation as the free red blood cell.

The first circulation of this type contains in the plasma-stream cells which enable the organism to establish a very simple type of respiration. Such a condition in its earliest inception is represented by the circulatory apparatus of Amphioxus. With the elevation to more advanced vertebrate organization this mixed lymphatico-haemal type of circulation no longer suffices for the growing respiratory requirements, and, in response to the resulting functional demand, a separation of the original single circulatory system into two divisions begins to develop. One of these divisions continues on the hereditary lines as the rudiment of the future lymphatic system in the narrower sense, with cell free' plasma, while the other, arising primarily in response to the ever increasing demand of the tissues for oxygen, differentiates as the anlage of a haemal circulation with the haemoglobin cell as its distinctive biochemical and morphological character.

In this process the bloodvascular system has gradually and continuously assumed more and more complex relations to the organism and has taken on successively higher and higher biochemical activities in addition to the original function of serving in the respiratory exchange, until it has morphologically and physiologically become the predominant vascular structure. The separation from the lymphatic channels has in consequence become more and more pronounced, until it has progressed in mammals to the point where, as the final outcome of the process, two distinct sets of vessels are established side by side. The component channels of one set, further specialized as arteries, veins, blood capillaries and heart, are closely associated and mutuaUy interdependent, and give structural expression to the importance attained in the course of phylogenetic evolution by the haemal vascular system. The second set, that of the lymphatic channels, is in its main extent independent of the first, simpler and more primitive in its organization, and more restricted in function, closely interlocked with the venous division of the bloodvascular sjrstem which it in certain functional respects supplements.

This division must of course have occurred gradually, and rather by multiplication of channels than by septal division of a single preexisting system into two components. Naturally this process should offer in the phylogenetic series many stages in which the division is still incomplete, and hence the gradual solution of peripheral organic continuity between hsemal and lymphatic vascular organization, in proceeding from the lower to the higher types, is, even with our present scanty knowledge, quite evident in the vertebrate series. No recent contributions to comparative vatecular anatomy have done more to clear this question and to advance our correct perspective than the investigations of Favaro^ on vascular organization in fishes.

The Italian anatomist has described a very close and intimate relationship in teleosts between lymphatic and venous organization. In several forms the same vessels appear to function at certain periods as lymphatic channels, while at others they are physiologically venous in character. Hand in hand with this interchangeable functional relationship goes a marked complexity of the lymphatic and venous hearts.

The investigations of Allen^ have led to similar results.

In ascending the zoological scale we encounter, together with the increasing independence of haemal and lymphatic vascular organization, a progressive and phylogenetically most significant reduction in the number, complexity and histiological differentiation of the lymph hearts. Favaro's demonstration of the primitive relationship between the teleostean lymphatic and venous system now completes the chain between the conditions presented by Amphioxus and those encountered next above the fishes in the urodele amphibians. This ascent is marked by a more definite separation of venous and lymphatic pathways, although the still large number (14-20) of the iu*odele veno-lymphatic hearts recalls the former more intimate association of the two systems.


Favaro, Guiseppe, 1905: II cuore ed i seni caudali dei Teleostei Ahi R, 1. Veneto di sc. lettr et arti, 1905-06, tome 65- Part II. Append, alia Dispensa, bet. 1906, Venejin 1906- Anat. Ana. Bd. 27, p. 879-880. Archivio di Fisiologia, Bd. 2, l-asc. 5.

^ Allen, W. F.: Distribution of the Subcutaneous Vessels in the Head Region of the Ganoids, Polydon and Lepisosteus. Washington Acad. Sc. Proc., vol. ix, pp. 79-188, 1907. Distribution of the Subcutaneous Vessels in the Tail Region of Lepisosteus. Am. Jour. Anatomy, vol. viii, pp. 50-89, 1908.


A reduction of the lymph hearts to two pairs, an anterior and a posterior, is next encountered in the aniu*e amphibians. In the reptiles only a single (posterior) pair of these organs is carried into the adult organization. The anterior lymph heart appears, however, during the ontogenesis in a rudimentary form, as determined by recent examinations of the 7.5 nun. and 9 mm. embryo of Scleroporus undulatus.

In birds the posterior lymph heart is retained throughout life in some forms. In others, as shown by Sala,' it develops in the embryo, but disappears soon after the assumption of free life. While the subject is still under investigation, there is reason to believe that the presence of a rudimentary anterior lymph heart in birds during the ontogenesis can be demonstrated, and that this structure effects the final lymphatico-venous connection.

In mammals, finaUy, a reduced single pair of anterior organs, the jugular lymph sacs, alone persists, as far as we at present know, as the sole remnants of the extensive antecedent series of lymphatico-venous connections and serves as the bond between the otherwise completely separated venous and l3anphatic systems.

Thus the more prominent and highly specialized the hsemal vascular system appears as compared with the lymphatic, the higher in general is the animal organization possessing this type. Conversely, in descending the zoological series, the individuality and independence of the two systems diminishes steadily until they finally merge into the single conmion archaeal anlage.

'Sala, L.: SuUo sviluppo dei cuori linfatici e dei dotti torarcici nell' embrione di poUo. Roma, 1900.


As previously stated* the lymph hearts represent in this evolutionary process, on the one hand, the line along which the gradually acquired organic separation of the blood-vascular and lymphatic systems proceeds, while on the other hand, they play in the various phases of this process of segmentation the important role of links between the lymphatic and the hsemal channels, which, in ascending the scale, are becoming progressively and incre^ngly more independent of each other.

For obvious physiological and mechanical reasons this original connection can never be entirely interrupted, but we see in the relative organization of the lymphatic and venous systems in the mammalia, in comparison with the conditions formed in lower vertebrates, the highest degrees of this phylogenetically acquired independence.

I have in a previous publication* pointed out the fact that the possibility exists in the plan of manmialian lymphatic organization for the establishment of lymphatico-venous connections at other points in the adult than those afforded by the typical connections of the anterior lymph heart or jugular lymph sac with the veins at the common jugular and jugulo^subclavian angles. Such connections, if they exist in certain forms, must be interpreted with our present knowledge of mammalian lymphatic organization, as retentions of other primitive lymph heart bonds between the lymphatic and venous system which, in the greater number of mammalia, are not developed and carried into the tjT)ical adult plan, but which may, while atypical for the general class, appear in certain specialized forms.

It is quite conceivable that development on these lines would lead to results which would serve the mammalian physiological demands equally well, if not better, than the prevalent type of manunalian lymphatic organization. It is possible that the reported instances of the termination of the thoracic duct in one of the azygos veins or its tributaries in the adult human subject can be interpreted as variations depending for their genesis on the atypical development and retention of a lymphatico-venous heart formation at points other than the ones normally concerned in the production of the jugular lymph sac. The reported cases are, however, not sufficiently authentic to accept them at their apparent face value, and the available evidence is too scanty to warrant the assumption that these variations, if they exist, are of a progressive character tending toward the eventual reduction of the thoracic duct and the substitution for the same of a paore direct connection of the abdominal lymphatic channels with the venous system.

Huntington: The Genetic Interpretation of the Development of the Mammalian Lymphatic System. Anatomical R«5ord, vol. ii, nos. 1 and 2, 1908, pp. 1-44. » Loc. dt., p. 30.


The more our knowledge of comparative vascular anatomy grows, the clearer the perception becomes, that in spite of the apparent structural and functional differences between venous and lymphatic organization, the two systems are but parts of an originally single and united whole, and hence must be primarily of equal and identical origin. The genetic unity of all vascular structure is a proposition which is constantly becoming more self-evident. Even if it were not for the direct observations to the contrary, this fact alone negatives the assumption of the derivation of the systemic lymphatics from the veins as secondary products of their endotheUel proliferation. The line of reasoning above outlined, if carried to its logical conclusion, stamps the entire complicated haemal vascular apparatus of the higher vertebrate types as the genetic descendant of a preexisting simple lymphatic vascular system. In other words, in place of considering our modem Ijinphatics as derivatives from the veins, I believe that in a correct valuation of the relative position of veins and lymphatics, we are obliged to regard the lymphatic system as the primary organization, from which gradually in the phylogenesis the bloodvascular system has been derived. In spite of the predominance of haemal over lymphatic structure in the higher forms, the latter should be recognized as the phylogenetically older primarj'^ structure.

The separation between the two has in the evolutionary sense become more and more pronounced, until it has progressed in the mammal to the point where, even in the ontogenesis, the anlages of both are laid down independently. But their common genetic basis is to be found in the vascular strands of the early mesoderm. It is however not at all improbable that the mammalian lymphatic system, as we at present know it, in the relatively few forms that have been carefully studied, is still in the evolutionary sense undergoing progressive changes which in their broader significance trend toward further reduction and simplification of the lymphatic, as compared with the haemal vascular organization. In view of the predominant association of the mammalian lymphatic channels with intestinal alimentation and the metabolic processes of digestion, such further evolutionary modification of lymphatic organization from the type now prevalent in mammalia, would in aU probability be in the direction of still greater development oi this physiological character. This might find structiu'al expression in the higher development of the intestinal lymphatic complex and a coincident reduction of the general lymphatic channels at present associated with them. The mammalian lymphatic system would under these conditions correspond mainly to the hepatic-portal venous channels and would convey the products of digestion directly to the systemic venous current.

The organic principle of the above described phylogenetic separation of a haemal from a preexisting single primitive lymphatic circulation repeats itself within the far narrower circle of the former in the phylogenetic division which leads, through the Dipnoean and Perennibranchiate lines, to the replacement of the primitive single branchial type of respiration and circulation by the double cycle of the air breathing forms. This change in environment, with its resulting enlarged scope of vertebrate life, has led step by step to more highly organized structural types within the framework of the primitive haemal vascular system, through which stages the single-hearted, coldblooded branchial form has advanced to the double-hearted, warm-blooded pulmonary type.

In its physiological significance this general evolutionary process again means primarily vastly greater and more rapid tissue metabolism or combustion in the broad sense. The structural response to this functional demand is strikingly given in the phylogenetic (and ontogenetic) development of the intra-cardiac and intra-aortic septa. We encounter here on a large and unmistakable scale, and associated with an evident biochemical function, the division of part of the originally simple and imifonn hsemal vascular system of cardiac chambers and truncus arteriosus into two bilateral and equivalent elements. This change is effected primarily not by addition from wiOwvt (except the neomorphism of the pulmonary vein) of something new but by a change and re^arrangement of parts already existing within the framework of the primary bloodvascular system. If, therefore, as McClure and I have definitely proved,* the manmialian jugular lymph sac, or cervical lymph heart, is secondarily separated from the manunalian embryonic pre- and postcardinal veins, this process of division of originally single hsemal channels into completely separate elements is not genetically a new process, confined to the lymphatico-venous terminal, but follows on a smaller scale and much more obscurely, genetic lines already laid down in the division of the primitive single heart tube into its completely distinct dextral and sinistral components.

The question here involved is of great and far reaching importance in establishing the correct relative position and value of the hsemal and lymphatic vascular systems.

If the metabolic demand for increased and more rapid supply of oxygen is capable of calling into existence, within the already organized confines of the hsemal division of a simple vertebrate circulation, the structiu*al changes leading to the divided heart and the lung in place of the antecedent branchial type of circulation and respiration, then the same force is evidently suflScient to derive, in far earlier phylogenetic stages, from the primitive general non-cellular circulatory system, a separate set of channels conveying plasma with free haemoglobin cells as the circulating medium, and developed primarily in the service of the oxygen-carbon dioxide exchange of the tissues.


• Huntington and McClure: The Anatomy and Development of the Jugular Lymph Sacs in the Domestic Cat. Anatomical Record, vol. ii, nos. 1-2, 1908, pp. 1-18.


In this way there comes to be established the phylogenetic anlage of a secondary bloodvascular system, derived from the primitive general vascular apparatus circulating non-cellular plasma. With the appearance of the hsemd system the dis* tinction between it and the persistent portion of the primitive vascular organization as a lymphatic system develops.

Thus the primitive simple hsemal system, subsequently destined to xmdergo imder the stimulus of phylogenetic advance, a complete secondary division, was in its own turn originally segmented from a simpler antecedent circulation of lymphatic type for the pmpose of satisfying the earliest demand of the tissues for oxygen by becoming the carrier of hsemoglobin cells, while the persistent elements of the earUer system are retained as lymphatic vessels serving a new physiological purpose under changed conditions of metabolism.

As stated above the series of lymph hearts would in this genesis of the bloodvascular system represent points where the original continuity of lymphatic and haemal elements is retained, in a specialized and modified form for definite physiological purposes. The number and distinctive character of these lymph hearts would then naturally diminish in proceeding seriaUy from the lowest to the highest types, coincident with the serially developed greater and greater independence of the hsemal and lymphatic divisions of a general vascular system.

This change impUes an enormous degree of adaptability and structural response to fimctional demands. Many examples of this extreme plasticity of vascular organization are encountered throughout the entire formative period of the manmiaUan embryo, in which the bloodvascular system is the predominant agency of nutrition as well as respiration. This character appears not only in the crystallization of definite assymetrical arterial and venous pathways from an antecedent symetrical bilateral type, but also in many of the more intricate relations of the bloodvascular channels to the temporary and the future permanent metabolic demands of the tissues. Thus, for instance, in the placentalia the vitelhne veins appear in the r6le of the earliest embryonic nutritive and respiratory channels. They subsequently, in the placentd period, yield this part to the secondarily involved umbilicals. Their own primary signifiance is lost and remains in abeyance throughout the whole of the placental epoch, to suddenly reassert itself when the hepatic portal channels, as the direct descendants of the afferent vitelline veins, assume with, the establishment of intestinal aUmentation at birth, the important share in the nutritive processes of the body which they are henceforth to maintain throughout the life of the individual. The anlages of these vessels were, so to speak, side-tracked for the very considerable umbilical or placental period of embryonic and foetal existence. But they continued to develop dm^ing this entire period of functional displacement and obscurity, and became associated with the growing alimentary canal, in anticipation of the moment when, with the first establishment of post-foetal conditions, they resumed their original significance and entered into their now definite and permanent function as nutrient afferent hepatic vessels.

In the same way the entire extensive series of structural changes within the three divisions of the bloodvascular system, leading finally to the establishment of the pulmonary circulation, is developed in anticipation of the sudden assumption of pulmonary respiration at birth.

This law of anticipatory ontogenesis is of very wide application and expresses especially the cardinal character of extreme adaptability, both to present requirements and future needs of the organism, in all developing vascular structure.

It is quite possible, that the lymphatic vessels, which we must recognize in the broad phylogenetic ground plan of vascular organization, as the primary and earliest channels, appear in the complicated and highly specialized manmiaUan vascular system of predominantly haemal type, in a subordinate and secondary position, owing to genetic influences of this general character.

They are formed, during the embryonic period, just as the portal and pulmonary channels are formed, but like these, they develop in anticipation of assuming their functional activity only with the altered environment and changed nutritive conditions of the post-foetal period.

In this sense they appear as secondary structures, allied to the all important hsemal embryonic channels, just as the placental viteUine veins, within narrower phylogenetic limits, appear subordinate to the new bloodvascular conditions dependent upon the acquisition of the umbilical vein as the main embryonic nutritive and respiratory vessel, in the phylogenetic ascent from the vitelUne to the placental phase of embryonic development.

This brings us to the question of the comparison between the ontogenesis of the mammaliam systemic lymphatics and the lymphatic organization of the lower vertebrates. Briefly stated, our observation as to the development of the mammalian lymphatic vessels, can be summed up as follows:

1. The first anlages of the bloodvascular channels and of the systemic lymphatic vessels in the mammalian embryo are identical. These common anlages are formed by independent intercellular mesodermal tissue spaces, which, in enlarging, become Uned, in obedience to the mechanical pressure effects of the clear fluid contents of the spaces, with endothelium.

2. The spaces become confluent to form larger and continuous channels. The bloodvascular system differentiates genetically from the lymphatic system by the secondary inclusion of the speciaUzed mesodermal haemoglobin cell of the blood islands in the clear non-cellular stream of the plasma circulating during the primary stage in the hsemal system of channels in response to the cardiac pulsations.

The systemic lymphatic channels continue on the other hand, to convey a clear fluid containing no, or only a few, cellular elements.

3. This histogenetic identity, and the fact that subsequently the only criterion defining respectively the early embryonic bloodvascular and lymphatic channels is the red blood ceU content of the former, precludes definite differentiation of the two sets of vessels prior to the period at which the haemal channels acquire their distinctive free cellular elements.

4. Hence we must accept three chronological possibilities in regard to the ontogenetic period at which these anlages begin to appear. :

a. The bloodvascular and lymphatic channels develop siniul

12 GEO. S. HUNTINGTON

taneously as capillary anlages side by side, and subsequently differentiate firom each other as above detailed.

b. The lymphatic anlages are the first to develop. Subsequently a portion of the conunon system, or a second generation of equivalent channels, differentiates as the hsemal component of the vascular system, in contradistinction to the persisting primary lymphatic system.

c. The bloodvascular system is ontogenetically the first to develop in the mammalian embryo. The lymphatic anlages appear secondarily as an equivalent system of mesodermal spaces, which subsequently unite. The resulting channel system does not acquire the free circulating blood cells characteristic of the hfiemal division, but finally gains access to the blood vascular system by union with the jugular lymph sacs, derived from the veins, and is thus enabled to enter as an integral component into the triple constitution of the general circulatory apparatus.

From the phylogenetic standpoint the second of the above enumerated possibilities is the one which is most consistent with the haemo-lymphatic organization as seen in its general evolution in the vertebrate series. At the same time the last of the three possibilities appears from the evidence at hand to represent most acciu'ately the conditions encountered in mammalian embryos. The separation between bloodvascular and systemic lymphatic organizations has here not only progressed to a degree in which even the ontogenetic anlages of the two channel systems are laid down independently of each other, but has further resulted in placing their first appearance into different embryonic periods.

From the phylogenetic standpoint this must be regarded as the result of factors operative in the speciaUzation of the highest vertebrate types, and not as the original common condition. The mammalian ontogenetic relationship between the haemal and lymphatic anlages appears as an expression of the tremendous development which in the evolution of the higher zoological types, the bloodvascular system has gained over the primary lymphatic circulation. This paramount influence of haemal over lymphatic vascular development has even reversed the relative ontogenetic period in which the first distinct anlages of


PHYLOGENESIS OP VERTEBRATE VASCULAR SYSTEMS 13

each system appear. The bloodvascular organization has gained the complete ascendancy, the lymphatic has been relegated to a secondary position, with highly curtailed and specialized function. Moreover, as above stated, the actual assumption of this function has been in the mammalian ontogenesis postponed to the end of the placental epoch, and the assumption of individual nutrition with the eatabUshment of the definite postnatal conditions.

Compared with the position of the lymphatic circulation in the ancestral series, one is almost tempted to characterize its development in the placental embryo as the reversional appearance of a system, formerly of much greater extent and importance, but now to a large extent replaced by more modem zoologies^ acquisitions, and retained only in a modified and reduced form with greatly restricted functional application.

At any rate, there is no radical inconsistency in the observed facts, either of the phylogenetic or ontogenetic history of vertebrate lymphatic vessels.

In respect to their genesis in the mammalian embryo, it makes but Uttle difference as to exact embryonic period in which they make their first appearance as definite lymphatic anlages.

Their development may be synchronous with that of the earliest haemal channels, or precede these, or finally, as seems to be actually the case, they may first appear distinctly after the main embryonic bloodvascular lines have been laid down.

Their ultimate secondary union with each other, and then with the venous system through the intervention of the comphcated jugular lymph sacs, and the entire character of the completed adult lymphatic-system as a ^* shadow-picture" of the venous organization, suggests strongly that the macMnalian lymphatic vessels have phylogenetically acquired this secondary position relative to the dominant haemal vascular system.

This subordination of lymphatic to bloodvascular structures manifests itself not only in the morphological relations existing ontogenetically and in the adult between the two systems, but the same influence has operated to retard the embryonic appearance of the first definite lymphatic anlagen to a period in which the


14 GEO. S. HUNTINGTON

blood-vascular organization has already assumed clear cut and definite character.

We thus reach the end-link in the long chain of successive diflferentiations which lead through the vertebrate series to the final stage in which the greatest attainable degree of independence between lymphatic and haemal vascular structiu*e has been reached, and in which the primitive relative value to the organism of the two systems has been reversed, in obedience to the law which has stamped the bloodvascular system as the main organic line of evolutionary progress.

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