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General Considerations.
==General Considerations==




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The Epibranchial Sense Organs.
==The Epibranchial Sense Organs==




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The Gustatory Organ.
==The Gustatory Organ==




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This view has been opposed by Peter (1901) ; he contends that an unpaired olfactory plate occurs in the rest of the vertebrates in the region of the neuropore, and I can from my own observations confirm his statements. The first anlage of the olfactory organ in man is formed by a paired convex area, covered by thickened epithelium (sensory epithelium), situated near the point where the anterior neuropore has closed. A%n Wyhe (1882) has maintained that the olfactory nerve is only apparently the first cranial nerve ; in reality it is the second, the optic being the actual first and the succession being reversed by the cranial flexure. This would also be the case with the corresponding sense organs. Nussbaum (1900) has also reached the same conclusion, and says, "Consequently the spot where the optic anlage leaves the brain has been secondarily transferred from the dorsal to the ventral surface and at the same time pushed caudally, on account of the forebrain flexure. By this the optic nerve, as Van Wyhe has already pointed out, has become the second cranial nerve, although it was originally on the dorsal surface in front of the olfactory nerve, which is counted as the first cranial nerve in adult vertebrates." Hatschek (1909) has also quite recently made the same statement. The question depends upon what is to be regarded as the anterior end of the medullary plate. If the infundibulum repre
This view has been opposed by Peter (1901) ; he contends that an unpaired olfactory plate occurs in the rest of the vertebrates in the region of the neuropore, and I can from my own observations confirm his statements. The first anlage of the olfactory organ in man is formed by a paired convex area, covered by thickened epithelium (sensory epithelium), situated near the point where the anterior neuropore has closed. A%n Wyhe (1882) has maintained that the olfactory nerve is only apparently the first cranial nerve ; in reality it is the second, the optic being the actual first and the succession being reversed by the cranial flexure. This would also be the case with the corresponding sense organs. Nussbaum (1900) has also reached the same conclusion, and says, "Consequently the spot where the optic anlage leaves the brain has been secondarily transferred from the dorsal to the ventral surface and at the same time pushed caudally, on account of the forebrain flexure. By this the optic nerve, as Van Wyhe has already pointed out, has become the second cranial nerve, although it was originally on the dorsal surface in front of the olfactory nerve, which is counted as the first cranial nerve in adult vertebrates." Hatschek (1909) has also quite recently made the same statement. The question depends upon what is to be regarded as the anterior end of the medullary plate. If the infundibulum represents its original anterior end and the regions of the chiasma and the recessus opticus have been formed by suture, and if the optic vesicles, as must also be assumed, are dorsal structures corresponding to the part of the edge of the medullary tube which has in this region united by suture, then Van Wyhe is correct. I re gard this primary question, however, as not yet settled, and accordingly cannot regard it as settled that the olfactory nerve really lies caudal to the optic (compare also Keibel; 1889).
 
 
DEVELOPMENT OF THE SENSE.-ORGANS. 189 sents its original anterior end and the regions of the chiasma and the recessus opticus have been formed by suture, and if the optic vesicles, as must also be assumed, are dorsal structures corresponding to the part of the edge of the medullary tube which has in this region united by suture, then Van Wyhe is correct. I re gard this primary question, however, as not yet settled, and accordingly cannot regard it as settled that the olfactory nerve really lies caudal to the optic (compare also Keibel; 1889).





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XVI. The Development of the Sense-Organs

By F. Keibel.



General Considerations

Not only are stimuli perceived that come to the body from the exterior, but also the internal conditions, such as the position of the joints and the tension of the muscles. For the reception of both kinds of stimuli special apparatus, the sense-organs, may be developed. On account of the surpassing importance and the variety of the external stimuli, the sense-organs for their reception are much more perfectly and variously developed than are those for the perception of internal processes ; indeed it is even doubtful whether the tendon and muscle spindles should be regarded as sense-organs, and the lamellate bodies have recently on good grounds been denied that character (Ramstrom, 1908, and von Schumacher, 1907). Furthermore it is to be noted that the entire external skin possesses in addition to other functions that of a sense-organ ; its development, as well as that of the hairs and hairdisks which belong to it, has been considered in a special chapter.


In the higher sense-organs (the eye and ear) and the olfactory organ the portions which receive the stimuli are derived from the ectoblast. The gustatory organs, as will be shown later, are possibly, indeed probably, derived from the entoblast. As regards the organs of internal sensation, free nerve terminations must be regarded as the stimulus receptors, just as they are in the external skin ; that which at first sight appears to be the sense-organ should really be regarded as accessory apparatus and is developed from the mesoblast.


The Touch=cells, the Lamellate Corpuscles (Vater=Pacinian Corpuscles), the End=bulbs (W. Krause's Corpuscles), the Touch=corpuscles (Meissner's Corpuscles), the Sexual Corpuscles.


It has just been pointed out above that free nerve terminations must be regarded as the stimulus receptors in all the organs mentioned here. As to the development of the accessory apparatus, if the skin and its organs, which have been specially considered, be left out of the question, very little is known. The development of the lamellate corpuscles in man has not, to my knowledge, been investigated in recent times.


Henle and Kolliker made some observations upon them in 1844. These authors recognized them in the sixth month of preg 180

DEVELOPMENT OF THE SENSE-ORGANS. 181 nancy as cell masses without any special arrangement of the cells ; in the new-born child they appeared to be quite similar to those of the adult, except that they were smaller and had little or no fluid between the lamella?. W. Krause (1860) found them relatively far developed at a much earlier period. "A corpuscle from the volar surface of the index-finger of a fetus at the end of the fifth month of pregnancy, which he measured, had a length of 0.29 mm. and a breadth of 0.11 mm.; the outermost capsule was quite distinct and the innermost was also recognizable; the rest were merely indicated and possessed an enormous number of oval nuclei arranged lengthwise. Transverse fibres could not be detected. The nuclei just mentioned occurred also in the central cavity, which was 0.225 mm. in length and 0.018 mm. in breadth, , and in its axis was a very distinct, glistening terminal filament which had a diameter of 0.0038 mm. and ended close to the peripheral part of the inner cavity with a slight enlargement." Davydow (1903) has recently investigated the development of the lamellate corpuscles of the cat, but I know of his results only through Weinberg's abstract of them in Schwalbe's Jahresbericht, Neue Folge, Bd. x (1904). According to this the Vater-Pacinian corpuscles in their earliest stages consist of a small number of connective-tissue cells. By rapid increase these cells soon form round or oval cell groups; the roundish elements become altered centrally into elongated ones, and finally all are employed in the formation of the lamella? of the developing Pacinian corpuscle. In the new-born cat a rapid increase in the number of Pacinian corpuscles takes place by budding. In the division the Timofejew apparatus is usually formed from a common fibril-bundle, an arrangement which indicates the possibility of a functional cooperation of several Pacinian corpuscles.


There are also some observations on the development of the touch-corpuscles by W. Krause (1860). He found them in a seven months' fetus in the tips of the papilla? of the vola manus. According to Krause the new-born child possesses in its little fingers and toes just as many touch-corpuscles as does the adult individual, and it must therefore possess a more delicate sense of distance. New touch-corpuscles and especially terminal corpuscles do not form after birth. With these results those of Ranvier (1880-1881) do not quite agree. Eanvier starts with observations made by Langerhans (1873) on young children. According to him the development takes place essentially after birth. In the new-born child one sees in vertical sections through the finger pulp at the summit of most of the papillae, immediately below the first row of epithelial cells, some transverse stria? and, somewhat deeper, an island of roundish mesoblast cells. The transverse stria? represent a nerve telodendron : the nerve ascends directly to the summit of the papilla and there divides into a small number of branches, which terminate in enlargements. These branches lie horizontally, as if they had been forced up through the cell island against the bases of the epithelial cells. In children 50 days old the nerve telodendron has developed greatly, its branches are more numerous and thicker and the mesoblast cells have penetrated between them (Fig. 120). In the sixth month the upper lobe of the composite corpuscle has reached its definitive form. It is well delimited, and in its interior one sees PV^H a certain number of telodendra separated by - S^fof cells that are weakly flattened transversely.


The second lobe is in process of formation. At the base of the first lobe one sees, that is to say, a new nerve telodendron and beneath this is a group of roundish cells that seem about to penetrate it. The contradictions contained in the puscie'ofachiidonodays" observations of Krause and Eanvier are pertreated with gold chloride. } ia p S on i v apparent ones. Eanvier has not n, nerve; b, nerve telodendron, between the branches examined the youngest stages and Krause has of which the cells of the sub- , • ^ \ n n i i*»ji n jacent node are penetrat- not considered the development of the finer S-^ioJ^^E Parts of the small organ. Krause (1869) has ri I is- a 7 ti ) aild Wjss ' Leip " a ^ S0 i nves tigated the development of the spherical end-bulbs in the conjunctiva bulbi of man; in a six months' fetus they had the appearance of masses of nuclei or cells, nevertheless they already possessed a distinct investing membrane.


The Epibranchial Sense Organs

Epithelial thickenings that may be found dorsal to the branchial clefts of embryos of from 4 to 12 mm. may be regarded as rudimentary sense-organs. These thickenings, which are termed sense-placodes, occur in connection with the vagus, glossopharyngeal, and facial nerves, and less distinctly with the trigeminus, cells being given off from the ganglia of these nerves: they may then be transformed into small epithelial pouches. See regarding them Keibel and Elze, Normentafel zur Entwicklungsgeschichte des Menschen (1908), Plates 10-45, Ingalls (1907), and the chapter in this work on the development of the peripheral nervous system. The placodes have probably a great importance from the standpoint of comparative anatomy and embryology. It is supposed that the auditory and olfactory organs have been formed from such placodes, and the lens of the eye has also been derived from a placode; this may have been originally the actual sense-organ. On this point see Brachet (1907a and 1907b).


The Gustatory Organ

The tongue is frequently spoken of simply as the organ of taste, and one may say of a person that he has a good tongue just as one might say he "has a good eye ; but on the one hand the tongue is not merely a gustatory organ, and on the other hand, the organs that are receptive for taste, the taste-buds, are not limited in their distribution to the territory of the tongue. Accordingly the development of the tongue will be treated along with that of the digestive tract, and we have to discuss here in the first place the development of the taste-buds. Brief consideration must also be given to those papillae of the tongue which are to be regarded as accessory organs of the gustatory sense. The territory within which taste-buds are found in man is quite extensive. Their principal situation in the adult individual is on the papillae vallatae; but they have also been described as occurring on the papillae foliatae and the papillae fungiformes, on the under surface of the tongue on the plica fimbriata (Ponzo, 1905 1 , 1905 2 , and 1907), on both surfaces of the epiglottis and also in the mucous membrane of the larynx itself, and in the region of the arytenoid cartilages (Davis, 1877). They are also said to occur in the anterior surface of the soft palate, especially in the neighborhood of the uvula (A. Hoffmann, 1875, W. Krause, 1876). Von Ebner (1899) has not been able to find them in this situation, and J. SchafTer (1898) believes that the thickened ends of papillae have been confused with taste-buds; Ponzo (1907), however, has recently stated that he has found them in the human fetus on the palatine tonsil, on the palatine arches, and on both surfaces of the soft palate. Such contradictions are probably to be explained by the fact that, as will be seen, the taste-buds are at first more widely distributed than they are later on, and undergo a partial retrogression which apparently is not of quite the same extent in all individuals. Very generally the gustatory organs have been regarded as being of ectodermal origin (see Schwalbe, Lehrbuch der Anatomie der Sinnesorgane, p. 36) ; this view is not, however, free from objection. It is not possible, it is true, to delimit exactly in the mouth cavity the ectoblastic and entoblastic territories; but the majority of the tastebuds lie undoubtedlv within the entoblastic territorv, and even although epithelial encroachments are possible, yet it seems difficult to suppose that the ectoblast has penetrated into the region of the larynx. The first thorough investigations of the development of the taste-buds in man were undertaken by Tuckermann (1889, 1890 \ 1890 2 ), who also reviewed the older literature, for Hoffmann (1875) and Lustig (1884) had already published statements concerning the fetal conditions. Tuckermann failed to find taste-buds in a fetus of ten weeks, but did find them in one of fourteen weeks ; he concluded, therefore, that they were formed during the twelfth week of intra-uterine life. The first statements, accompanied by figures, concerning the actual histological differentiation of the buds were made by Qraberg (1898), and his account will lie followed here.


In a fetus of about three months (11 cm. vertex-sole length) this author could not recognize any anlagen of the papillae vallatae, but he found two ridges of the mucous membrane at the back part of the tongue which were placed obliquely and met in the median line to form an angle open anteriorly. These ridges are the foundations for the papillae vallatae. The epithelium covering the ridges is growing even at this stage into the stratum proprium in the form of simple invaginations and is dividing the ridges into papillae. The first anlagen of the taste-buds are accordingly to be found in this fetus, but they are not as yet clearly denned (Fig. 121). The basal cells of the epithelium have lost their usual low cylindrical form and have increased in size noticeably. It is noteworthy that already in this earliest stage of development a nerve is in connection with that portion of the epithelium from which a taste-bud is differentiating, and Graberg believes that it may have a direct influence on the differentiation. Fig. 122 shows a further developed, well-defined taste-bud with a gustatory pore, from a fetus of 21.3 cm. vertex-rump measurement; a differentiation of the cells of the taste-bud into extrabulbar, basal, and pillar cells has also taken place to some extent, and, in addition, there are also present cells of an indifferent nature. So soon as they have become well differentiated the cells of the taste-bud reach the surface of the epithelium; then the gustatory pore is formed by the epithelium at the sides of the taste-bud increasing in thickness while the cells of the bud itself have almost completed their growth in length. The appearance of the taste-buds and their degree of development are in general subject to great variation. In the new-born child the different kinds of cells which constitute a bud are readily recognizable in transverse sections, neuro-epithelial cells, pillar cells, basal cells, and the extrabulbar cells; Graberg failed to find only the rod-shaped cells of Hermann, but, on the other hand, he believed that he could distinguish the striated margin of the inner gustatory pore, or ciliary corona of Schwalbe, as well as the hairs projecting into the pore. Many taste-buds undergo degeneration during the latter portions of intra-uterine life and after birth, and the degeneration process affects the firstformed buds situated on the upper free surfaces of the papillae vallatae, furthermore those on the papilla? fungiformes and those on the anterior surface of the epiglottis, on the tonsils, the soft palate, and on the plica fimbriata. Thus, Kiesow (1902) in almost mature fetuses in the majority of cases found taste-buds on the lingual surface of the epiglottis; after birth they vanish. According to Stahr (1901) the abundance of buds on the different kinds of papillae is associated with the degree of elaboration of the form of the papillae, their size and number. The vallate papillae are late to become fully formed, and when they do the papillae fungiformes assume a less definite form; they become relatively smaller and less numerous, and their epithelium partly loses its buds and becomes cornified. In the new-born child taste-buds occur on all the fungiform papillae. The significance of the different kinds of papillae for the function of taste alters during the life of the individual. The fungiform papillae have their greatest abundance of taste-buds, and with that their chief period for functioning as taste-organs, in the new-born child ; for the vallatae and the f oliatae these conditions occur in the adult. As regards the degeneration of the taste-buds on the upper surfaces of the papillae vallatae, Graberg finds that in fetuses of 24.5 and 39.5 cm. their outlines become indistinct and the nuclei of their cells shrivel. Occasionally leucocytes seem to invade them. The degenerated buds are carried to the surface and thrown off by the growth of the epithelium.



Fig. 121. — Frontal section through a papilla vallata of an 11 cm. human fetus. (After Graberg. Schwalbe's Morphol. Arbeiten, vol. 8, 1898, PI. 11, Fig 1.) a, places at which the formation of tastebuds is beginning; n, nerves.



Fig. 122. — Frontal section through a papilla vallata of a 21.3 cm. human fetus. (After Graberg, Schwalbe's Morphol. Arbeiten, vol. 8, 1898, PI. 11, Fig. 4.) o. indifferent cells; c, extrabulbar cells; d, basal cells; e, gustatory pore; p, pillar cells.




Fig. 124 Fig. 125 Figs. 123-125. — The summits of three taste-buds from a human fetus of 21.3 cm. a, in Fig. 123, indication of the gustatory pore, in Fig. 124, its anlage, and in Fig. 125, outer gustatory pore; b, gustatory canal; c, inner gustatory pore. (After Graberg, Schwalbe's Morphol. Arbeiten, vol. 8, 1898, PL 11, Figs. 8-10.)



The papillae vallatae, f oliatae, and fungiformes may properly be regarded as organs accessory to the taste-buds. The first appearance of the fungiform papillae is shown in the Normentaf el of Keibel and Elze in Plates 62, 64, and 66, in embryos less than 20 mm. in length. Graberg has described and illustrated by some diagrams (Fig. 126, a-d) the development of the papillae vallatse. The ridges that precede the anlagen of these papillae have alreadybeen described, and also the process by which they are broken up into the individual papillae. The annular walls are formed from definite epithelial growths, derived from the epithelial ridges that bound the primitive papillae, and, lateral to these, extending down into the stratum proprium. The stratum proprium on its part then projects up into the epithelial thickening, raising the epithelium over it and thus producing on the free surface of the mucous membrane surrounding the papillae a slight elevation, which is the anlage of the annular wall. The fossae are formed by the fusion of small clefts that develop in the epithelial downgrowths that separate the papillae. The glands of Ebner appear as solid outgrowths which extend laterally from the lower edges of the epithelial downgrowths. Later they acquire a lumen by the degeneration of their central cells, but even in the new-born child they are not everywhere fully developed. Until after birth the growth of the fungiform papillae is mainly in length (Stahr, 1901), the fungus shape being acquired with the development of secondary crops of papillae, by which a second stage in the growth of the papillae is characterized ; now for the first time can the papillae be said to have a foot and a head. The secondary papillae have already appeared in children of a few months, and in these all fungiform papillae still bear taste-buds, whereas in the tongue of the adult fungiform papillae without buds occur. In the adult the epithelium often cornifies to form long tips, yet papillae also occur whose epithelium is in part cornified and in part bears buds. Transitions between vallate and fungiform and between fungiform and filiform papillae do not occur.



Fig. 126, a-d. — Diagrams illustrating the development of the vallate papillas and their adnexse. (After Graberg. Schwalbe's Morphol. Arbeiten. vol. 8, 1898, p. 121-122.) o, "primary," b, "secondary" epithelial downgrowths: c, anlagen of glands of von Ebner; d, fossae: e, annular wall.



Bibliography

(For the lamellate corpuscles, touch-corpuscles, and the gustatory orgai Davis, C. : Die becherfbrmigen Organe des Kehlkopfes, Arch, fur mikr. Anat., vol. 14, 1877. Davydow : Materialien zur Kenutnis der Entwicklung des peripheren Nerven systems, Dissert., Moskow, 1903. vox Ebxer, V.: in Kolliker's Handbuch der Gewebelehre, vol. 3, p. 21, L899. Graberg, J.: Beitrage zur Genese des Geschmacksorganes des Mensehen, Schwalbe's Morphol. Arbeiten, vol. 8, p. 117 (12 plates and 4 text figures), 1898. Henle, J., and Kolliker, A. : Ueber die Pacini' schen Korperchen an den Nerven des Mensehen und der Saugetiere, with 3 plates, gr. 4to. Meyer and Zeller. Zurich, 1844. Hoffmann, A. : Ueber die Verbreitung der Geschmaeksorgane beim Mensehen, Virchow's Arch. f. path. Anat., vol. 62, 1875. Keibel, F., and Elze, C. : Norrnentafel zur Entwicklungsgesckichte des Mensehen, Jena, 1908. Kiesow, F. : Sur la presence des boutons gustatifs a la surface linguale de 1'epiglotte humaine avec quelques reflexions sur les rneines organes, qui se trouvent dans la muqueuse du larynx, Arch. Ital. Biol., vol. 37, p. 234. 1902. Krause, W. : Die tenninalen Korperchen der einfach sensiblen Nerven, Hannover, 1860. (Compare Hex-twig's Handbuch, vol. 2, p. 330.) Die motorischen Endplatten der quergestreiften Muskelfasern, Hannovei*, 1869. Anatomie, vol. 1, 1876. Langerhans, P.: Ueber Tastkorperchen und rete Malpighii, Arch, fiir mikr. Anat., vol. 9, 1873. Lustig, A. : Beitrage zur Kenntnis der Entwicklung der Geschmacksknospen, Sitzungsber. Akad. Wiss. Wien, vol. 89, part 3, p. 308, 1884. Ponzo, M. : Sulla presenza di calici gustativi in alcune parti della retrobocca e nella parte •nasale della faringe del feto umano, Giornale d. R. Accad. di Med. Torino, vol. 68, also in Monit. Zool. Ital., vol. 16, 1905 \ Sur la presence de bourgeons gustatifs dans quelques parties de l'arriere bouche et dans la partie nasale du pharynx du foetus humain, Arch. Ital. Biol., vol. 43, 1905'. In torn o alia presenza di organi gustativi sulla faccia inferiore della lingua del feto umano, Anat. Anz., vol. 30, 1907. Ramstrom, M. : Anatomische und experimentelle Untersuchungen iiber die lamellosen Endkorperchen im peritoneum parietale des Mensehen. Anat. Hefte. vol. 36, Part 109, 1908. Ranvier, L. : Nouvelles recherches sur les organes du tact, Comptes Rend. Acad Sci. Paris, vol. 91, p. 1087, 1880. Traite technique d'histologie, p. 706-707, 1880. Schumacher, S. von : Ueber das glomus coccygeum des Mensehen und die glomeruli caudales der Saugetiere, Verhandl. Anat. Ges. "Wiirzburg, Anat. Anz., vol. 30, Suppl., 1907. Schaffer. J. : Beitrage zur Histologie menschlichen Organe. V. Mundhohle. Schlundkopf, Sitzungsber. Akad. Wiss. Wien.. vol. 106 (Oct.. 1897), 1898.


Stahr, H. : Ueber die papillae fungiformes der Kinderzunge und ihre Bedeutung als Geschniacksorgan. With 4 plates. Zeit. fur Morphol. und Anthrop., vol. 41, p. 199, 1901.


Tuckermann, F. : On the Development of the Taste-organs of Man, Journ. of Anat.and Physiol., vol. 23, p. 559, 1889.


Further Observations on the Development of the Taste-organs of Man, Journ.of Anat. and Physiol., vol. 24, p. 130, 1890 1 . On the Gustatory Organs of the Mammalia, Proc. Boston Soe. Natural Hist., vol. 24, p. 470, 1890\ The Olfactory Organ.




As is well known, the gnathostomatous vertebrata may be divided into monorhinous and amphirkinous forms. By their monorhinous condition the Cyclostomes stand in contrast to the rest of the vertebrates. KupfTer (1884) has sought to bridge the gap between the two conditions, and his views have for that reason secured much acceptance. He regards the ciliated groove at the anterior neuropore of Amphioxus as an olfactory organ. The Cyclostomes, in addition to the unpaired anlage of the olfactory organ, the " unpaired olfactory placode," situated close to the neuropore, had also paired organs situated more laterally, the lateral " olfactory placodes," which secondarily fused with the unpaired one ; the rest of the vertebrates in addition to the lateral olfactory placodes had also the anlage of the unpaired placode, but this latter degenerated.


This view has been opposed by Peter (1901) ; he contends that an unpaired olfactory plate occurs in the rest of the vertebrates in the region of the neuropore, and I can from my own observations confirm his statements. The first anlage of the olfactory organ in man is formed by a paired convex area, covered by thickened epithelium (sensory epithelium), situated near the point where the anterior neuropore has closed. A%n Wyhe (1882) has maintained that the olfactory nerve is only apparently the first cranial nerve ; in reality it is the second, the optic being the actual first and the succession being reversed by the cranial flexure. This would also be the case with the corresponding sense organs. Nussbaum (1900) has also reached the same conclusion, and says, "Consequently the spot where the optic anlage leaves the brain has been secondarily transferred from the dorsal to the ventral surface and at the same time pushed caudally, on account of the forebrain flexure. By this the optic nerve, as Van Wyhe has already pointed out, has become the second cranial nerve, although it was originally on the dorsal surface in front of the olfactory nerve, which is counted as the first cranial nerve in adult vertebrates." Hatschek (1909) has also quite recently made the same statement. The question depends upon what is to be regarded as the anterior end of the medullary plate. If the infundibulum represents its original anterior end and the regions of the chiasma and the recessus opticus have been formed by suture, and if the optic vesicles, as must also be assumed, are dorsal structures corresponding to the part of the edge of the medullary tube which has in this region united by suture, then Van Wyhe is correct. I re gard this primary question, however, as not yet settled, and accordingly cannot regard it as settled that the olfactory nerve really lies caudal to the optic (compare also Keibel; 1889).


The sensory epithelium of the olfactory placodes is at first, especially ventrally, imperfectly marked off from the epithelium that covers the rest of the head. This condition was found by Keibel and Elze (Fig. 127) in an embryo of 4 mm. in its greatest length (Normentafel, Plate 10) ; the olfactory areas were already distinguishable in an embryo of 3 mm. described by Bromann (189G) (Normentafel, Plate 11), while Hammar (Normentafel, Plate 9) could not find them in an embryo with a greatest length of 4.7 mm.




Fig. 127. — (From Keibel and Elze, Normen- Fig. 128. — (From Keibel and Elze, Normen tafel zur Entwicklungsgeschichte des Menschen, tafel zur Entwicklungsgeschichte des Menscben Fig. 9 e.) X30. R, olfactory area; Vh, forebrain. Fig. 12 k.) X30. R, olfactory area; Vh, forebrain.


The delimitation of the olfactory epithelium is more perfect in the embryo of Plate 14 of the Normentafel (4.9 mm. nape-breech length, 4.7 mm. vertex-breech length) (Fig. 128). x In an embryo with a greatest length of 5.3 mm. (4.6 nape length) the olfactory areas are still convex, but are beginning to be more sharply delimited dorsally. They then become flattened (Fig. 129) (Normentafel 21, greatest length 6.75 mm.) and later begin to be depressed in their dor so-lateral part (Fig. 130) (Normentafel, Plate 24, in an embryo of 6.5 mm. greatest length = nape-breech length, vertex-nape length 4.7 mm., vertex-brow length 3.0 mm., age fairly certainly 21 days ; also Normentafel, Plate 25, greatest length = nape length 6.25 mm.). In an embryo of 8 mm. (Normentafel, Plate 30 and Fig. 21 b) the olfactory area, according to Hammar, is feebly depressed, and in its caudal portion, which has deepened into a pocket, the nasal groove has formed. This embryo corresponds with that which His (1880-1885) figured in Fig. 29, p. 46, of the third part of his Anatomie menschlicher Embryonen, and which has also been figured by Kallius (1905) and has formed the basis of his description; I repeat His's figure here as Fig. 132 for comparison, although I have some doubts whether it correctly represents the normal conditions. The nasal fossa is surrounded by a marginal swelling which is interrupted below toward the maxillary process. The lateral limit of the swelling covers only a part of the medial wall of the nasal fossa. A process on the medial limb His identified as the processus globularis (p. g.?), and further down, where the medial edge comes into relation with the maxillary process, there is a larger projection, and internal to this a small round, rather deep and sharply margined depression (J. 0.?), which His regarded as the earliest anlage of Jacobson's organ. I have never seen the earliest anlage of Jacobson's organ of this form in man, it appears in my opinion as a groove, and the projection also which His identifies as the processus globularis I would not so identify, but would suggest that the swelling near the maxillary process and external to the depression designated by His as Jacobson's organ is much more probably the structure that should be identified with the processus globularis. I follow, accordingly, my own observations here and must leave it for later investigations to decide which are correct.


1 Delia Vedova (1907) has already described olfactory fossae in an embryo of 4.7 mm.



Fig. 129. — (From Keibel and Elze, Normentafel zur Entwicklungsgeschichte des Menschen, Fig. 16 i.) X25. Ao, aorta; At. d., right atrium; D. A., ductus venosus Arantii; Lb., liver; Mg, stomach; R., olfactory area; 9. R. S., ninth body somite; <S. v., sinus venosus; V. c. p., posterior cardinal vein; Vh, forebrain; W. G., Wolffian duct.



Fig. 130. — (From Keibel and Elze, Normentafel zur Entwicklungsgeschichte des Menschen, Fig. 18 f.) X20. Ao. W., aortic root; D. C. d. (s.), right (left) Cuvierian duct; N. v., vagus nerve; Oe., ossophagus; Rg., olfactory fossa; 3. R. S., third body somite; S. I., septum primum; Tr., trachea; Vh., forebrain; Vtr. s., left ventricle; Vv. v. d. (s.), valvula venosa dextra (sinistra).



Some further observations are necessary for a comprehensive account of the development of the nasal fossae, and the formation of the face must be recalled. In a stage such as that shown in Fig. 133 the oral fossa is bounded above by the frontal process, to the right and left by the maxillary processes, and below by the mandibular processes. Since a. projecting angle is formed where the right and left mandibular processes meet % the entrance into the oral fossa has a pentagonal form. The two upper lateral angles, where the maxillary processes are better developed, extend as the lachrymal grooves as far as the eyes; they therefore bound the frontal process laterally. In the territory of the frontal process there is now formed, as we have seen, on either side a nasal area (His). 2 The nasal area is at firsl convex, in correspondence with the form of the surface of the frontal process, and even when the epithelium has become sharply delimited on all sides it is not recognizable on superficial examination. Only when it becomes flattened, and especially when it begins to be depressed, is it distinct. These first processes may be determined essentially by growth of the epithelium covering the nasal area (Peter, 1900 and 1902), but in man observations for determining this point have not been made. Later the margins of the area become raised by the growth of the surrounding mesoderm and thus deepen the nasal fossa, or rather the nasal grooves, for the wall surrounding the olfactory area is interrupted orally. In this stage, shown in its earliest stages in Fig. 134, the anlagen of the olfactory organ are separated by almost the entire breadth of the frontal process. It is customary to term the portion of the frontal process lying between the areas the middle frontal process and the lateral portions the lateral frontal processes; these latter coincide almost exactly with the lateral nasal processes, which project lateral to the olfactory grooves. Quite different is the relation of the medial nasal processes to the middle frontal process; they originally occupy only a very small lateral portion of it. The further transformation of the nasal grooves into the primitive nasal cavities is brought about by the maxillary processes coming into contact and fusing with the lower ends of the medial nasal processes. These lower ends project markedly forward and are known as the processus globulares (His). The fusion takes place from within outwards and occurs as the processes meet, so that the primitive nasal cavities in man, as in the rest of the mammalia, 3 are never connected by a groove with the primitive mouth cavity ; there is no reservation of a choana, so that the primitive nasal cavities, which open anteriorly by the external nares, are blind




Fig. 131. — (After Hammar, from Keibel and Elze, Normentafel, Fig. 21 b.) X 25. A, eye; H, cerebral hemisphere; Nf, olfactory area; Nr, nasal groove.



Fig. 132. — (After His, from Anat. Menschlicher Embryonen, III, p. 46.) X 20. View of the anterior portion of the head of a human embryo from the left side. P. g f, marked by His (without ?) as the processus globularis; J . O t, marked by His (without f) as Jacobson's organ.



Fig. 133. — Head end of an embryo seen from in front. (After Rabl, Entwicklungsgeschichte des en face. (After Rabl (1902), Entwicklungsgeschichte Gesichtes, 1902, and corresponding practically with des Gesichtes.) This corresponds almost with Fig.


Fig. 134. — Head of an embryo of 8.3 mm. N L. in front. (After Rabl, Entwicklungsgeschichte des en face. (After Rabl (1902), Entwicklungsgeschichte Gesichtes, 1902, and corresponding practically with des Gesichtes.) This corresponds almost with Fig.


Embryo M of His.) X 20. XIV of the Normentafel of Keibel and Elze. X 10.



3 Echidna alone forms an exception. (Seydel, Denkschr. med. nat. G-es., Jena, Vol. 6, 1899.)


sacks and are at first shut off from the mouth cavity (Hochstetter, 1891 and 1892, Keibel, 1893, Delia Vedova, 1907). By the coming in contact of the maxillary processes with the processus globulares, the nasal grooves become gradually closed and the external nares more and more narrow; finally, the lateral nasal process comes into contact with the medial one and assists in bounding the primitive nasal cavity laterally and below, as I can state in confirmation of Peter's (1902) results. At the close of this developmental process (Fig. 135) the upper border of the mouth is formed by the maxillary processes and the medial nasal process and the lower border of the nares by the medial and lateral nasal processes. (Compare also Vol. I, p. 83, Fig. 64.) The primitive nasal cavities are shut off from the palate, but their epithelium is in connection with that of the mouth cavity by a plate of epithelium (Fig. 136). While this epithelial plate becomes transformed at its posterior end into a membrane, the bucconasal mem




Fig. 135. — Model of the anterior part of the head of a human embryo of 10.5 mm. (After Peter, from Hertwig's Handbuch, vol. Hi, p. 53, Fig. 60.) Ventral view. X12.5. J. R., Jacobson's groove; L. N. F., lateral, M. N. F., medial nasal process; P. G., processus globularis; 0. K. F., maxillary, U. K. F„ mandibular process.


brane (Hochstetter), and finally tears, the primitive choanae being thus produced, the mesoderm of the maxillary processes and of the lateral nasal processes is growing toward that of the medial nasal processes; it eventually destroys the epithelial plate and forms the primitive palate. This can be regarded as consisting of a facial portion, from which the upper lip is formed, and an oral portion, the premaxillary palate. The mesoderm of both portions is furnished by the maxillary and medial nasal processes, the lateral nasal processes participating only at the lower border of the nares.


While the developmental processes just described have been taking place, the middle frontal process has been gradually becoming smaller and the two nasal openings have been brought closer together. On the middle frontal process there may be distinguished laterally the medial nasal processes, each ending in a processus globuiaris, between these the trough-like depressed infranasal area (His), and above this the area triangularis (His), above which, again, is the part of the head which projects owing to the anlagen of the cerebral hemispheres (Fig. 135). The infranasal area is separated from the area triangularis by an angle that is at first indistinct but later becomes more sharply defined and from which the border and tip of the nose are formed; the area triangularis becomes the dorsum of the nose and the infranasal area is transformed into the septum. His believed that the nasal septum had a paired origin, because in the stages in which the nasal openings are close together the medial nasal processes are almost in contact in the median line and the whole of the portion of the middle frontal process lying between them has become a



Fig. 136. — (After Keibel and Elze, Normentafel zur Entwicklungsgeschichte des Menschen, Fig. 32 a.) X20. D.n.l., nasolachrymal duct; H., cerebral hemisphere; J.O., organ of Jacobson; p. G., primary palate.


Fig. 137. — (After Keibel and Elze, Normentafel zur Entwicklungsgeschichte des [Menschen, Fig. 24 i.) X20. H., cerebral hemisphere; J. O., Jacobson's organ.


rather deep groove. This groove may, as a rule in many animals but exceptionally in man, persist, forming a median lip cleft. Normally this embryonic cleft closes by the growth of the mesoderm forcing the epithelium out of the cleft, not by the medial nasal processes coming into contact and uniting, so to speak, by a suture. In my opinion, therefore, it is not proper to speak of an actual paired anlage of the nasal septum, although the material for it is thrust in toward the median line from the right and the left.


We have now in the first place to consider the anlage of the organ of Jacobson and that of the conchce, and then the transformation of the primitive into the definitive nasal cavities.


The organ of Jacobson 4 in man appears as a groove-like depression on the medial wall of the olfactory fossa. I have seen its earliest anlage in an embryo of 8.5 mm. greatest length (Normentafel, 32). Fig. 137 shows it in section in an embryo of 9.2 mm. greatest length, 8.8 mm. NL. (Normentafel, Plate 38). It is seen further developed (Fig. 136) in an embryo of 14 mm. (Normentafel, Plate 51). The groove has deepened and it then closes from behind forwards. The mouth of the cylinder produced in this way narrows, and on its medial wall there forms olfactory epithelium, in connection with which, however, no cilia have yet been observed ; glands also develop. In the human fetus the organ lies in the anterior portion of the nasal septum ; in a fetus of about ten weeks Kallius (1905) found it on both sides with a length of 0.42 mm.; its entrance was narrow and led into a greatly (about tenfold) enlarged sack. About this time one can readily observe, as Kolliker first pointed out, that branches of the olfactory nerve pass from Jacobson's organ to the brain. 3 In the twentieth week of fetal life the organ, according to Kallius, has reached the height of its development. Later it varies greatly and may completely degenerate, even in the embryo, but, on the other hand, it is not infrequently found and has often been described in the adult. (Compare on this point Merkel, 1892.)



Fig. 138. — Section through the head of a human embryo of 18.5 mm. greatest length. (Collection of Robert Meyer, No. 32; Normentafel of Keibel and Elze, Plate 64, Fig. XXI.) X 15. G.L., palatal process; J.O., Jacobson's organ; point of union with the nasal cavity; S., nasal septum, in which there is a common blastema for the cartilage of the septum and Jacobson's cartilage; Z., tongue, in which the musculature is beginning to differentiate. The tongue (Z) lies between the palatal processes. An early stage of the dental ridges may be recognized.


  • The organ of Jacobson was discovered by Fr. Ruysch in 1703.



Fig. 139. — Section through the head of the embryo of Fig. 13 !. The section lies 150 m further caudad. The cerebral hemispheres and one eye have been cut, but Jacobson's organ is no longer visible. The lingual and hypoglossal nerves are entering the tongue. The lettering as in Fig. 138. X15.


A case in which it was present in the adult in a quite exceptional degree of development has recently been recorded by Mangakis (1902). Although Peter (1901 2 , p. 71) again repeats the view already frequently stated, that the organ is often destroyed in extra-uterine life as the result of frequently occurring catarrh of the nasal mucous membrane, yet I agree with Merkel (1892) that there are no sufficient grounds for this opinion, since the organ often disappears in the fetus. A supportive apparatus for Jacobson's organ is also formed, Jacobson's cartilages. According to Mihalcowics (1898), these cartilages separate from the cartilage of the nasal septum, but, like Kallius (1905), I find that they arise independently. At first only one cartilage anlage is to be seen on either side, "but in the fourth to the fifth month one sees several, usually three, a larger one that is frequently somewhat curved, and two smaller" (Kallius). Originally also the cartilages are situated close to the organ of Jacobson, but later they separate from it. Their relationship to Jacobson 's organ has been called in question and they have been described as the vomero-nasal cartilages (see Spurgat, 1893 and 1896) ; in my opinion this is incorrect, for comparative embryology shows that these human cartilages are to be homologized with the typical Jacobson 's cartilages of the mammals. How the comparison is to be followed out in detail, when in later stages three cartilages are present, will be considered further on. Delia Vedova (1907) believes that the lateral wall of the cartilaginous nasal skeleton also takes part in the formation of these cartilages, and, with Mihalcowics (1898), regards them as the remains of a plate that in other animals closes the nasal cavities below. That Gegenbaur (1886) should deny the occurrence of an organ of Jacobson in man, when the relation of the olfactory nerve to the organ during development had previously been clearly shown by Kolliker (1883), is surprising.



  • Delia Vedova incorrectly doubts this.





Fig. 140. — Section through the head of a human embryo of 2 mm. greatest length. (Collection of Robert Meyer, No. 321; Normentafel of Keibel and Elze, Plate 84.) X15. G.L., palatine processes; J. K., Jacobson's cartilage; J.O., Jacobson's organ; M.K., Meckel's cartilage; O., eye; S., cartilaginous nasal septum; U.M., inferior concha (maxilloturbinal). The bony anlagen (maxillary and mandibular) are black.


Gegenbaur identifies the structure that is here described as the organ of Jacobson with the septal gland first described by Steno. From what has been said, there cannot be any doubt but that in the human Jacobson's organ we have a portion of the olfactory organ which possesses special functions in many animals, but has become rudimentarv in man.



198 Some stages in the development of Jacobson's organ are shown in Figs. 139 to 144, and the development of Jacobson's cartilages may be followed in Figs. 138, 139, 140, 143, and 144. It will be seen that they arise from a blastema common to them and the cartilage of the nasal septnm (Figs. 138 and 139) ; from their first appearance, however, they are sharply marked off from the cartilage of the septum (Fig. 140). Fig. 141 shows the right side of the nasal cavity under higher magnification. The formation of nerves in connection with the organ of Jacobson is taking place, and in the epithelium of the nasal cavity a peculiar doublelayered condition is noticeable. The most superficial cells are arranged like a covering layer, except in those regions which are already recognizable as sensory epithelium. The same condition obtains also in older stages, as may be seen from Fig. 143 (fetus of 4.2 cm. sitting height), and it certainly deserves a thorough investigation. Fig. 142 shows a stage intermediate between Figs. 140 and 143. The palatal processes have come into contact, but the epithelium has not yet been forced out by connective tissue along the line of suture. The right and left nasal cavities are still in continuity below the septum. Fig. 144 shows some sections taken from a frontal series through a fetus of 47 mm., the sections following one another in apicocaudal direction. In Fig. 144, A, two very short lateral processes {p) branch out from the septal cartilage and very soon separate from it (Fig. 144, B, p), but the septal cartilage, which is very thin in places, is never connected with any of the other cartilages. Basal from these processus laterales ventrales (Zuckerkandl, 1909) there then appears on either side a cartilage plate (Fig. 144, C, pi), which soon divides into a medial and a lateral portion (Fig. 144, B, I and m) . While first the cartilage indicated by I and then that indicated by p disappear, a small piece separates from m (Fig. 144, E and F). According to Zuckerkandl (1909), this much is at least certain, that the medial portion of the plate pi becomes Jacobson's cartilage and that the portion p is to be homologized with the processus nasalis lateralis of other forms. He does not suggest an homology for the cartilage I.



Fig. 141. — A portion of the right side of Fig. 140 more enlarged. X 95. J.O., Jacobson's organ; U.M., inferior concha (maxilloturbinal). Over a considerable portion of the epithelium of the nasal cavity there is a sort of covering layer.



Fig. 142. — Frontal section through the head of a human embryo about 8 weeks old, taken 1.9 mm. from the most anterior point of the head. (After Kallius, in Bardeleben's Handbuch, vol. 5, Section 1, Part 2, p. 202, Fig. 70; somewhat modified.) D., dental anlage; G. L., palatal processes; J. K., Jacobson's cartilage; J. O., Jacobson's organ; Max., anlage of the maxilla; U. M., inferior concha (maxdlloturbinal); Z., tongue. XI 5.



The development of the concha takes place entirely in the region of the sensory epithelium, — that is to say, in the region of the primitive nasal cavities. The conchal apparatus of the human nose, like the human olfactory organ in general, is reduced, so that it is impossible to obtain a satisfactory understanding of it without the aid of comparative anatomy and embryology.


The way toward a satisfactory understanding of it has been shown especially by the work of Killian (1895, 1896, 1902) and Peter (1902 2 ); but the observations of Zuckerkandl (1887, 1892 x and 1892 3 ) and Schonemann (1901) should also be mentioned. According to Peter, the conchae arise as well on the lateral as on the medial wall of the primary nasal cavities, 6 the maxilloturbinal and nasoturbinal arising from the lateral and the ethmoturbinals from the median wall. Fig. 145 shows a section through the posterior portion of the olfactory fossa of a rabbit embryo of 3.5 mm. head length; the dorsal region of the medial wall is slightly bent away from the lateral one, and the slight swelling above the bend represents the first ethmoturbinal. How it is transferred from the medial to the lateral wall is made clear by Fig. 146 ; it is brought about by the ingrowth of the epithelium at x. In a similar manner two other ethmoturbinals are formed independently from the septal wall in the rabbit, in the region of the posterior blind sack of the nose (Fig. 147). The one which is first formed is in embryonic life completely divided into two secondary ridges by a groove. From the lateral wall the conchal structures which Peter terms the conchas obtectse are formed below the rostrally projecting border of the first ethmoturbinal. In front of these, in the region of a cleft which is bounded anteriorly by the sharply marked posterior border of the nasoturbinal (the processus uncinatus), the maxillary sinus is sinking in in a downward direction.



Fig. 143. — Frontal section through the nasal cavities and the palate of a fetus of 4.2 cm. (sitting height). (KeibePs collection.) X 15. J.K., Jacobson's cartilage; J.O., Jacobson's organ; U.M., inferior concha (maxilloturbinal); S., cartilaginous nasal septum.


  • Delia Vedova (1907) has recently opposed this view.




Peter has made it probable that the ethmoturbinals are formed from the medial wall in man also, but he has not been able to demonstrate it. As a difference in the human development as compared with that of the rabbit, it may be noted that the nasoturbinal is very rudimentary and develops very late; it becomes the agger nasi (Peter, 1901 2 , p. 64). In early stages the maxilloturbinal alone is present; it occupies the posterior two-thirds of the lateral wall throughout its entire height. Gradually it becomes more sharply marked off, especially ventrally; the groove thus formed becomes the inferior nasal meatus. It is interesting to note that in man a dorsal lamella is added to this concha in the fourth month (Mihalcowics, 1896 2 , p. 71), 7 so that at this stage it recalls the doubly coiled maxilloturbinal of many mammals. Only late does the agger nasi appear as a slight elevation above the inferior concha and in front of the first ethmoturbinal. In an embryo of 30 mm. vertex-breech length Peter finds a second ethmoturbinal behind the first, and behind this still other four in maximo may appear (Killian). That a new ethmoturbinal is interposed





Fig. 144. — Frontal sections through the nasal septum of an embryo of 47 mm. The sections have been taken from a series passing in the apicocaudal direction. (After Zuckerkandl, 1909.) 8, septum: p, ventral lateral process: pi, cartilage plate below p: m and I, portions formed from cartilage pi; according to Zuckerkandl, m becomes Jacobson's cartilage.


Fig. 145. — Section through the posterior blind sac of the olfactory organ of a rabbit embryo of 3.5 mm. head length. X 50. (After Peter, from Hertwig's Handbuch, vol. II 2 , p. 61, Fig. 69 a.) ET., ethmoturbunal; x., bend in the medial wall.


Fig. 146. — Section through the oral end of the olfactory organ of a rabbit embryo of S.5 mm. vertex-breech length. X 50. (After Peter, from Hertwig's Handbuch, vol. Ih, p. 61, Fig. 69 b.) ET., ethmoturbinale I; M.B.-N., bucconasal membrane.



Fig. 147. — Nasal cavities of a rabbit embryo of 13 mm. head length, seen from the medial side after removal of the upper part of the septum. X15. (After Peter, from Hertwig's Handbuch, vol. IIj, p. 60, Fig. 68 b.) A portion of ethmoturbinale I has been removed and its contour is indicated by a broken line. C. o., concha obtecta; D. N.-P., nasopharyngeal duct; D. St., Steno's duct; ET.I, first, ET.II, second ethmoturbinal; J. 0., Jacobson's organ; Lt., lamina terminalis; MT., maxilloturbinal; NT., nasoturbinal; S. m., maxillary sinus.


Fig. 148. — Lateral wall of the right nasal cavity of a fetus from about the ninth or tenth month. X 1.5. (After Killian, Arch, fur Laryngologie, vol. 3.) ET.I-ET.V, ethmoturbinale I-V; ET.II cd., ethmoturbinale II cms descendens; ET.I ca., ethmoturbinale I crus ascendens; ET.I cd., ethmoturbinale I crus descendens; MT., maxilloturbinale; NT., nasoturbinale; Si ra., first principal groove, ramus ascendens; 5i rd., first principal groove, ramus descendens; S. s., sinus sphenoidalis.


and grows out between two of those already present, as Zuckerkandl supposes, I cannot admit; nor can I agree with Delia Vedova's (1907) criticisms of Killian, whose preparations I have seen.



  • Compare also Killian (1896), PL II, Fig. 39, and the text-figures.



In the description of the succeeding developmental processes I follow Killian, differing from him only in that, with Peter, I do not term nasoturbinal (agger nasi) ethmoidale I, but contrast the nasoturbinal, maxilloturbinal, and conchae obtectae as lateral conchae with the ethmoturbinals which are medial conchae. Killian 's ethmoturbinale II is accordingly termed ethmoturbinale I in the figures taken from his works, and similarly with the others. Killian has acquiesced in this alteration of his nomenclature.


Fig. 149. — Lateral wall of the right nasal cavity of a fetus from the ninth or tenth month. XI. 5. (After Killian, Arch, fur Laryngologie, vol. 3.) MT., maxilloturbinale; NT., nasoturbinale; Sira., first principal groove, ramus ascendens; Si rd., first principal groove, ramus descendens; S. s., sinus sphenoidalis.





Fig. 150. — (After Killian, Arch, fur Laryngologie, vol. 13.) " ETi-ETv, ethmoturbinale I-V; NT, nasoturbinale; MT, maxilloturbinale; Si-St, first to sixth principal groove; Tb, opening of Eustachian tube.


Figs. 148 and 149 show the lateral nasal walls of two fetuses of the ninth to the tenth months; Fig. 150 is a combined diagrammatic figure representing the maximal number of ethmoidalia, an arrangement that only very rarely occurs. In addition to the maxilloturbinal and the nasoturbinal (agger nasi) five ethmoturbinals may be recognized, the free edge of each of the anterior ones forming a cms ascendens and a cms descendens, while where the two crura meet there is a more or less pronounced lobulus with a nodulus, which is to be compared with the tip of the ethmoturbinals of the mammals. In addition to these principal conchae Killian finds other accessory conchae in the principal grooves, and accessory grooves may also develop on the conchee. Fig. 151 shows the middle meatus of a human embryo of the sixth month ; the anterior part of the middle concha has been removed. One sees between the bulla ethmoidalis, which is formed by two conchas obtectae, and the processus uncinatus the inf undibulum ; in it lie three infundibular accessory conchae ; the groove between the upper and the middle one is marked Sim^s. Above the bulla ethmoidalis and the inf undibulum lies the upper part of the recessus ascendens, the frontal recess, with three frontal conchae bounded by four grooves. The development of the nasal cavities is complicated by the formation of the sinuses and the ethmoidal cells ; also fusions of grooves and parts of grooves occur (Killian), a phenomenon that may, at least in part, be regarded as a compensation for growth processes (Schonemann, Peter). Killian 's account is followed here. The three posterior crura ascendentia fuse throughout their whole extent, but only the anterior borders of the anterior three fuse, in such a manner that each unites with the upper surface of the next succeeding concha; thus recesses are formed under the anterior parts of the conchae, the recessus ascendentes, the first of which is the recessus frontalis, already mentioned. The rami descendentes IV-VI become completely obliterated, but the anterior three only partially, so that the free margins persist and form the definitive conchae, which, accordingly, represent only the crura descendentia of the original principal conchae. From recessus ascendens III a posterior ethmoidal cell may be formed frequently a cell then unites with it, which has its origin from the portion of the groove corresponding to the ramus descendens. The superior recess of the second groove also becomes a posterior ethmoidal cell, the groove itself becomes two cells, an upper and a lower, which are separated by an accessory concha (Killian, 1895 2 ). From the recessus superior of the first groove, whose upper part Killian has named the recessus frontalis, the upper and anterior ethmoidal cells (frontal cells) arise.



Fig. 151. — Middle nasal meatus of a human fetus of the sixth month. The anterior part of the middle concha, ET.I, has been removed. There are to be seen above the bulla ethmoidalis (Cim\ s.) and the processus uncinatus (Pr. u.) three frontal conchae (C. /1-3) on the lateral wall of the frontal recess and bounded by four frontal grooves (S.fi-t). (After Killian, Arch, fur Laryngologie, vo' 13.) MT., inferior concha (maxilloturbinale) ; Simi S., groove between the upper and middle infundibular accessory conchas.




In addition the recessus frontalis gives origin to the sinus frontalis ; indeed it may be completely transformed into that cavity or else the sinus is formed by one of the frontal cells protruding between the frontal conchas mentioned above. These concha? themselves usually vanish completely by fusing with one another and with neighboring structures; the third one may fuse with the upper end of the bulla ethmoidalis. The frontal sinus grows very slowly; it is still wanting at the time of birth (Delia Vedova, 1907) and at puberty has only the size of a pea.




Fig. 152 a and b. — Diagrammatic horizontal section through the right half of a human nose of primitive structure, a on an upper and b on a lower level. (After Killian, from Peter, Entwicklungsgesch. des Geruchsorgans, in Hertwig's Handbuch, vol. Hi, p. 68, Figs. 73 a and b.) C1-C5, principal conchse (ethmoturbinalia) ; below and between these the principal grooves with ascending (in a) and descending (in b) rami and with accessory (Cim.) and frontal conchse (C/.)j Inf., infundibulum; p. u., processus uncinatus; S. f., frontal sinus, formed directly (<2. m.) or indirectly (t. m.); S. m„ maxillary sinus; S. 8., sphenoidal sinus; S. n., nasal septum. The regions of fusion recognized by Killian are indicated by parallel lines.


The maxillary sinus develops at about the middle of the third month of intra-uterine life from the recessus inferior of the first groove. 8 At first it is only a small depression, which soon becomes a sack. In correspondence with its point of origin the fully formed sinns opens usually into the most posterior and lower portion of the infundibulum. Only after the eruption of the milk-teeth does it enlarge and begin to assume its characteristic pyramidal form; up to the fifth or sixth year of life it is round. In 10 per cent, of cases there now arises above the centre of the middle concha an accessory opening. The sphenoidal sinus is the most posterior part of the nasal cavity itself, separated by fusion processes ; as it increases in size it gradually penetrates the body of the sphenoidal bone. Two diagrammatic horizontal sections (Fig. 152, a and b) through the right half of the nose show clearly the relation of the embryonic arrangement to that of the adult.


  • According to Vedova (1907), it forms in the first half of the third month.




The inferior concha is the maxilloturbinal of comparative anatomy and the agger nasi the nasoturbinal. The middle concha is derived from the descending and a small part of the ascending portion of ethmoturbinale I.


The superior concha, when it is present, corresponds to the descending portions of ethmoturbinalia III and IV.


The superior meatus corresponds to the descending ramus of the second groove, the supreme meatus to the descending ramus of the third groove.


The accessory spaces may be classified as in the following table, in which the spaces between two principal conchae are regarded as of the first order, those between principal and accessory conchas as of the second order, and those between two accessory conchas as of the third order.



Level.



Upper

Lower

First principal groove.



I order: Frontal groove with frontal sinus (if developed di r rectly)

II order: First and fourth frontal cell (cell fl and cell /4)

III order: Second and third frontal cell (cell /2 and cell /3)

Second principal groove.



Third principal "groove.



I order: I II order: I order: Ascending Ascending

cell (cell 2a)

with frontal sinus (if developed indirectly) Upper cell (cell Upper and lower

Is) — middle ethmoidal cell (Bulla-cell). Recessus inf. (lower part of infundibulum) with maxillary sinus.



intermediate cell (cell 1 im. and t)

Upper and lower cell (cell 2s and 2i)

(cell 3a)

cell

Descending cell (cell 3d)

The septal folds, plicae septi, which may be seen on the nasal septum in fetal life, have nothing to do with the formation of the conchae; they lie in the region of the vomer and were seen and figured by Euysch (1703). Killian (1895) has studied them carefully and Figs. 153, a and b, are taken from his paper. Even in a three months ' fetus the epithelium in this region is thicker than elsewhere on the septum and the septal folds are formed by the ingrowth of furrows covered with epithelium. 9 They can first be recognized with the naked eye in the fourth month ; from that time on the proportion of septa on which they may be seen increases until the end of the eighth month and then diminishes again until birth. After birth the folds usually disappear ; if they persist they not infrequently form, by hypertrophy, tumor-like structures in the adult.


The development of the olfactory nerves has not been carefully investigated in man, but there is no reason for supposing that it takes place differently from what occurs in other vertebrates. In these the olfactory fibres are formed as outgrowths from the basal portions of the olfactory cells, extending to the brain. Some cells also wander out from the epithelium and are later to be found scattered along the entire length of the olfactory nerves, appearing like ganglion-cells ; their processes extend on the one hand to the olfactory epithelium and on the other to the brain. It has already been stated that olfactory nerve-fibres also develop from Jacobson's organ. Why nerve-fibres develop from only a very small portion of the primitive sensory epithelium of the olfactory fossa becomes clear when it is remembered how small the olfactory region of the fully developed nose is in comparison to the relative area of the primitive nasal fossa. For data on this point reference may be made to the observations of Brunn (1892), to Kallius in von Bardeleben's Handbuch, and to the account, given later on, of the relation of the primitive to the definitive nose.



Fig. 153a Fig. 153b Fig. 153a. — Nasal septum of a human fetus of 31 weeks, showing the plicse septi in unusual perfection. Natural size. (After Killian, Arch, fur Laryngologie, vol. 2.) PL s., plicae septi; J. 0., Jacobson's organ; J. W., Jacobson's swelling with septal folds; D. inc., upper middle incisor tooth.


Fig. 153b. — The same septum as is shown in Fig. 153a. The boundary of the vomer is shown (V.), otherwise the lettering is as in Fig. 153a.



The glands of the human nose, the small Bowman's glands, develop in the third and fourth months as solid processes. "In the new-born child they are weakly developed on the floor of the nasal cavity, but more abundantly on the medial surface of the inferior concha" (Kallius, 1905). They reach their complete development only after birth. 10 Delia Vedova (1907) states that a mucous degeneration of the epithelium of the nasal cavities occurs in early stages, but I cannot confirm this statement. He found the first cilia in a fetus of 5.7 cm. in the region of the lower concha and the middle meatus. In a fetus of 10.5 cm. (first half of the fifth month) they occur everywhere.


  • For further information concerning these structures and also for a possible function for them, see Killian (1895 1 ).




Up to the present the development of the primitive nasal cavities has alone been considered, and it must now be pointed out that, although the largest and most important part of the definitive nasal cavities arise from these, yet a portion of the primary mouth cavity becomes incorporated into the nasal cavities by the formation of the definitive palate and together with the primary nasal cavities forms the definitive ones.


Fig. 154. — Palate of a 3.8 om. human fetus. (After Dursy, from Peter, Entwicklung des Geruchsorgans, in Hertwig's Handbuch, vol. II», p. 56, Fig. 63.) Ac, external aperture; Ch., primitive choanae; <?., palatal process; z., anlage of the uvula.


It will be remembered that the primary nasal cavities open secondarily into the primary mouth cavity, the primary choanae being thus formed. With the more rapid growth of the facial region of the head these primary choanae increase in length and become slit-like. In this stage the nasal cavities are separated from the mouth cavity by the primary palatal processes (Dursy, 1869), which I do not always find well developed. These processes are formed by the margins of the primary choanae growing somewhat toward one another ; they lie in the region of the lower border of the medial frontal process and in that of the medial border of the maxillary process. The tongue, as soon as it has developed, lies close against the primitive choanae. Now (in the seventh to the eighth week) 11 the secondary palatal processes appear in the primitive mouth cavity on the inner side of the maxillary processes ; they begin at the anterior end of the primitive choanae and extend to the region of the pharynx; about their middle a projecting knob may be seen (Fig. 154, z), the anlage of the uvula.


  • 10 More detailed statements regarding these glands have heen made by Delia Vedova (1907). This author found their first anlagen as solid processes on the inferior concha and in the middle meatus of a 9.2 cm. fetus; in a fetus of 10.5 cm. he saw lumina appearing in them, and in one of 15 cm. their tubuli were richly branched.
  • 11 Delia Vedova (1907, 1908) gives for this, as well as for the general formation of the palate, earlier dates than do other authors.



The primary palatal processes appear at first as inconspicuous folds of the mucous membrane on the inner surface of the roots of the secondary palatal processes ; these are at first almost sagittal in position, their free edges looking downward and embracing the anlage of the tongue. This relation is shown in Figs. 138, 139, and 140.


In later stages the free edges of the secondary palatal processes are directed toward one another and the tongue is no longer between them. How this alteration in the relative positions of the palate and tongue has been brought about has been variously explained. His (1885, 1901) supposed that the tongue actively withdrew itself, 12 and if this did not happen properly a cleft palate results. In support of his view he refers to cases in which the tongue is withdrawn on one side and not on the other. Fick (1902) at first agreed with His; later he speaks in opposition to the idea of an upward bending of the palatal plates. According to his view, there must occur an extensive alteration in shape of the palatal and alveolar processes, which requires time for its accomplishment. He calls attention to a ridge in the pig, which, by further growth, produces a palatal plate having from the first its proper position above the tongue. According to this view the essential thing would be a change of form by growth and not active movement of the tongue. This is apparently the view held by Anna Polzl (1904), although her account of the process is not altogether clear to me. The closure of the secondary palate is made possible "by the tongue growing forward out of the space between the palatal plates without coming into it behind." The palatal plates themselves grow above the tongue in a horizontal direction, changing their form. Schorr (1908), who at my suggestion has recently investigated the question, comes to the conclusion that the change of position of the palatal processes is the result of a series of complicated phenomena depending on the principle of unequal growth ; the tongue and the palatal plates play quite independent parts in the process, but their parts must also be closely coordinated in order that a normal result may be brought about. The tongue changes its position and the secondary palatal processes become bent up by unequal, regular growth. A ridge, such as Fick described for the pig, Schorr could not find. "The depression and elongation of the tongue and the tendency of the palatal plates to gradually bend upwards produce a slow gliding movement between the lateral surfaces of the tongue and the medial surfaces of the palatal plates, a constant adaptation of one to the other and, in addition, a gradual change of position of one part after the other from before backwards." When the palatal plates have become bent up, they bound the secondary palatine cleft (Dursy), which becomes obliterated by the fusion of the plates. Contact between them takes place first behind their anterior ends and from there the fusion proceeds in both directions: it is completed in the eleventh or twelfth week. The epithelium originally present along the line of contact is forced out by the mesoderm, but portions of it may persist as epithelial pearls (Leboucq, 1881) and mav also give rise to cvsts (Dursy, 1869).

"His says, "This withdrawal (of the tongue) may be induced by active muscle centractions, — i.e., by depression of the lower jaw and by movements of the tongue."



Posteriorly the fusion extends as far as the uvula, which is formed from a paired anlage, — that is to say. it extends beyond the territory of the nasal cavities, and anteriorly also the plates do not fuse completely; in this region there later projects between them the anterior part of the septum, and only the nasopalatine ducts (ductus incisivi, Stenonis) persist, at first as solid cords of epithelium. After the palatal processes have fused in the median line, the two sides of the nasal cavity are still for a time continuous beneath the anlage of the septum (Fig. 142) ; later, by the fusion of the lower border of the septum with the palate, they become completely separated from each other and open by the secondary choanse into the pharynx posteriorly.


By the processes that have just been described a portion of the primary mouth cavity becomes added to the nasal cavity. In embryos one may indicate, with Schwalbe (1882, 1887, p. 51 et seq.), the boundary between the territories belonging to the primary and secondary nasal cavities by a line extending from the nasal opening of the incisive canal to the anterior inferior angle of the body of the sphenoid bone; later this line will not represent the boundary, since the posterior portions of the second and third concha 1 project beyond the line into the region of the short nasopharyngeal passage. The nasopalatine ducts, whose formation has already been described, later acquire for a time a lumen; then it disappears except at its upper and lower ends, which may to a greater or less extent persist. In the nasal cavities these remains of the nasopalatine ducts lie close to either side of the septum; on the palate they are on either side of the papilla palatina, which is formed in the region of the part of the nasal septum which takes part in the formation of the palate.


To recapitulate once more, the entire nasal floor is formed in the region jusl behind the external nares by a part of the lateral nasal process, by the premaxillary palate, by a small part of the lower border of the nasal septum, and by the anterior pari of the palatal processes of the maxilla'.


The external nares, as Kolliker (1879, p. 767) found and Retzius (1904 > and 1904 2 ), Peter (1901 2 , p. 72), and Delia Vedo (1907) have recently thoroughly demonstrated, are for a time (from the second to the sixth month, Kallius) closed by epithelial growths, formed (according to Peter), in man at least, al first only from the median walls. These epithelial masses are eg cially prominent at the anterior end of the nasal vestibule and for a time project from the external aares. Posteriorly they extend to the nasoturbinal. "In the fifth to the sixth month," according to Delia Vedova (1907) even in the fourth month, "the solution of the closure begins, apparently by the degeneration of the middle masses of epithelium. But for a long time one still finds remains of the epithelium in the open nares" (Kallius, 1905, p. 220).


The development of the nasal skeleton has been considered in connection with the skull ; only a few remarks, taken essentially from Kallius (1905, p. 212 et seq.), are necessary here. I may first point out that in the conchae of the nose the skeleton, as was formerly supposed, is not the primary structure. The swellings of the mucous membrane are the primary structures and the cartilage does not grow into these, but arises in them.


Quite briefly also the question as to the mechanism of the growth of the conchce may be considered. Schonemann (1901) confirms the view of Born and Legal (Peter, 1901 2 , p. 55) that the conchae are cut out of the lateral walls of the nasal cavities by grooves and that they are accordingly persistent portions of the nasal walls and not evaginations into the lumen of the nasal cavities; the epithelium must, therefore, grow towards those regions of the connective-tissue matrix where it finds the least resistance. Peter believes that Schonemann in this view has attributed to the connective tissue "an altogether too important part in the outgrowth of the epithelial grooves." It seems to me, on the contrary, that he underestimates the role of the connective tissue, whose growth also has its part to play in the formation and form of the concha; and elevations, and Kallius (1905, p. 203) does likewise.


The formation of the cartilage tissue begins in the seventh to the eighth week in the region of the body of the sphenoid bone. It advances thence apically in the septum; it is always further developed in this than in the lateral walls, where LI form- in the various conchae; in the wall of the inferior meatus and in the floor of the nasal cavity no cartilage forms. "When the cartili has formed in the regions mentioned, the cartilaginous skeleton (of the nose) consists of a sagittal unpaired plate in the nasal septum and of lateral paired plates, continuous with the former and forming the lateral walls and roof of the aasal cavity. Yet the union of the lateral and median plates is complete only in the anterior parts, in what will later be the roof of the external nose; posteriorly there is at first a wide opening, elongated in the sagittal direction, through which the fibres of the olfactory nerve pass. Then individual rods of cartilage develop, which divide the large opening into several smaller ones. By the increase of the partitions of the opening the cartilaginous cribriform plate is eventually formed." In a fetus of nine weeks the cartilaginous septum is continuous anteriorly with the lateral plates. These are curved in their lower portion and project into the maxilloturbinals ; they are not yet in connection with the orbital plates ; on their medial surfaces, those turned towards the septum, the anlage of the middle concha may be recognized as a quite small projection. Figs. 155 and 156 - e.g. are of a reconstruction from a fetus of twelve weeks; the small, somewhat indistinct ridge in front of the anlage of the cartilage of the middle concha (m.M.) forms the cartilaginous basis of the nasoturbinal. The orbital plates have now united with the nasal capsule; the cartilaginous anlage of the cribriform plate has not yet formed, but in its place there is a single large foramen. The Jacobson cartilages, whose development has already been described (p. 196, 197), are formed. Mention may also be made of the processus cartilagineus paranasalis (Mihalcowics), which later becomes incorporated in the upper jaw.



Fig. 155. — Reconstruction of the cartilaginous skeleton of a human fetus of about 12 weeks, seen from in front and partly from the side. (After Kallius, from Bardeleben's Handbuch, vol. 5, Part 1, p. 213, Fig. 77.) X30. c. g, crista galli; K. J., Jacobson's cartilage; Pr. p., processus cartilagineus paranasals.


The cartilaginous nasal skeleton in part becomes transformed into bone (ethmoid and inferior concha) ; another portion becomes overlaid by connective-tissue osseous anlagen, and where this happens the cartilage is for the most part absorbed. The cartilaginous portion of the septum and the cartilages of the external nose of the adult are persistent portions of it. These parts do not, however, remain unchanged, but are divided by ingrowing connective tissue (Mihalcowics, 1898, 1899, 1900, Kallius, 1905). Thus the cartilaginous septum usually becomes separated from the anterior portions of the lateral cartilages and remains per


DEVELOPMENT OF THE SENSE-ORGANS. 213 inanently connected with them only posteriorly; thus also are formed the alar cartilages, whose peculiar configuration begins to appear in the sixth month of uterine life.


The main points of the development of the external nose have already been described on p. 192. It was also pointed out there how greatly the parts originally lying between the nasal cavities were compressed from both sides ; this process also makes relative progress later. The entire space between the two processus globulares is represented in the fully formed individual only by the philtrum of the upper lip, the space between the entrances into the nasal cavities of the embryo only by the border of the nasal septum between the adult external nares; in this region there occurs occasionally an absolute reduction of the distance. His 13 found it in a five weeks' embryo to be 1.7 mm., in a seven weeks' one 1.2 mm., and in a somewhat older one 0.8 mm. The further formation of the external nose is dominated in later stages of development principally by the outgrowth of the middle portion of the nasal angle together with the tip of the nose, whereby the dorsum is formed. The nares, which originally looked directly forward, become directed downward ; their upper borders in the embryo lie at first very high, later, as may be perceived by a comparison with the position of the eyes, decidedly lower. The development of the individual form of the external nose begins only long after birth and lasts until puberty; it will not be followed further, but in a general way it may be remarked that the nose in women frequently retains more or less of its infantile habitus.



Fig. 156. — Reconstruction of the cartilaginous skeleton of the'right lateral wall of the nose of a human embryo of about 12 weeks. The cut surface formed by cutting through the roof of the nose is unshaded. (After Kallius, from Bardeleben's Handbuch, vol. 5, Part 1, p. 213, Fig. 78.) X 30. o. M., m. M., u. M., cartilages of the superior, middle, and inferior conch® ; K., wing of sphenoid bone; v. R., anterior border.


The development of the nasal cavities after birth has been thoroughly studied by Merkel (1885-1890) and Disse (1889). I give what are essentially the results of these investigators in the summary by Kallius (1905). "If one compares the nasal cavities of the child with those of the adult, one finds that the ethmoidal and maxillary portions are of equal height in the adult, while in the child the ethmoidal part is twice as high ; the maxillary portion must therefore gain considerably in height during growth. In the seventh year of life the definitive proportions are first acquired, and growth proceeds very slowly." In the new-born child the inferior concha reaches the floor of the nasal cavities, and the inferior meatus is therefore very narrow and the nasal exit also. The middle meatus is mainly used as the air-passage. Only after the milk dentition has fully erupted is there a better development of the nasal spaces. Thus the inferior meatus becomes pervious at about this time, although it remains quite narrow until about the seventh year. With the eruption of the molar teeth the maxilla, and with it the nasal cavities, elongates from before backward.

Cited from Kallius, 1905, p. 218.



With the formation of the body of the maxilla, which occurs at this time, its wall and the middle concha, which is fastened to this, undergo a downward movement. In this, however, the entrance into the maxillary sinus, which is of the proper size when the teeth break through, does not participate, and it therefore comes to lie at the upper part of the cavity which is enlarging downwardly.


When the change of dentition begins there is a cessation of the growth of the maxilla until puberty, when the change of the dentition is complete.


This corresponds in general with the growth of the skull, in which Merkel (1882 and 1885-1890) recognizes two periods; one lasts until the seventh year, then follows a pause, and the second period begins with puberty.


The growth relations of the upper jaw may also be determined from the position of the pharyngeal opening of the tuba auditiva; in the fetus it lies below the level of the palate, in the new-born child at its level, and in the second year of life at the level of the posterior end of the inferior concha (maxilloturbinal). Furthermore, the upper jaw is also pushed somewhat anteriorly during its growth, whereby the orthognathous face of the newborn child assumes a more or less pronounced prognathous form.


Some of the malformations in the nasal region may be explained as inhibitions of the development. The median lip cleft has already been referred to (p. 194) as an inhibition phenomenon occurring in the region of the upper lip and nasal septum. When disturbances of the formation of the primitive palate occur, the condition known as harelip is produced. To explain its formation it is not necessary to assume that the contact of the maxillary process with the processus globularis of the medial nasal process is entirely suppressed ; it may follow this, for if the growth of the mesoderm fails (see p. 193) the fused epithelia may again become separated by further growth. Naturally all variations may occur ; the lateral nasal process may come into contact with the medial one but the contact of the maxillary processes may fail, or, on the other hand, the fusion may fail in general (compare Fig. 157).


If the secondary palatal processes fail to come into contact, so that the formation of the secondary palate is incomplete, a cleft palate, palatum fissum, results. In such cases one side of the nasal cavity may be closed below by the fusion of the downgrowing septum with one of the palatal plates. A fusion of the nasal septum with the united palatal plates may also fail to occur. This inhibition is practically important if at the same time harelip occurs on both sides; then the portion of the upper lip that lies between the two clefts and the nasal septum protrude greatly, on


Fig. 157. — Defective formation of the lips and palate in a fetus of about three months. X 5. (After His, Anatomie menschlicher Embryonen, Part III, p. 43, Fig. 28.)

account of the septum not being anchored posteriorly. Naturally both harelip and cleft palate may occur simultaneously.


That the septal folds may not only persist but even become hypertrophied has already been stated.


Other malformations, such as the closure of the external nares and of the choanae, receive no explanation from the developmental history and are probably to be referred to intra-uterine pathological conditions.


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