On the Nerve Supply of the Radix Linguae of Newborn Dog. One of the present authors, KIKUCHI, has reported in detail on the innervation

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1 Arch. hist. jap. Vol. 19, n. 3 (May 1960). P Anat. Labor. of Prof. H. SETO, Tohoku Univ., Sendai. On the Nerve Supply of the Radix Linguae of Newborn Dog. Mizuho KIKUCHI, Shunsaku HATAKEYAMA, Hideo HONMA and Daihei YAMAGUCHI. (Received December 14, 1959.) One of the present authors, KIKUCHI, has reported in detail on the innervation of the dorsum and the facies inferior of the tongue of a newborn dog. The same author succeeded this work with a similar study on the innervation of the radix linguae of a newborn dog under the collaboration of the three coworkers named above, and discussing the results in comparison with the findings on the innervation of the same part of man (INAZAWA, 1949) and a few other mammals (YAMAMOTO et al., 1957 and KAMADA, 1958), obtained some interesting results as reported hereunder. The sagittal frozen sections and stained very beautifully by the SETO's silver impregnation method, as in the previous study. I. Individual Findings. The radix linguae of dog has neither the large-sized lingual papillae as found on the root of tongue of goat nor the smaller-sized ones as found on that of cat, but is thoroughly covered by an noncornified stratified flat epithelium as that of hedgehog. In hedgehog, the epithelium here contains papillae growing out of the propria, better developed in the fore part but less in the back part, but in the newvorn dog, no such papillae were found in formation. It is of interest that lingual follicle crypts are frequetly found formed by depression of the mucous membrane in the root of tongue of dog, surrounded by the so-called tongue follicles, large and small. These follicles on the tongue root of the newborn dog, however, do not protrude so much into the oral cavity as those on the human tongue. The lingual follicles on the tongue root of newborn dog, because of their known absence on the tongue root of goat, cat and hedgehog, were found especially conspicuous. They are far less well developed than in man, but in the prpria beneath the epithelium facing such follicles, lymph nodes or groups of lymphocytes are often fully developed, the latter frequently infiltrating into the very epithelium (Fig. 1). Not rarely, however, such lingual follicles are entirely devoid of lymphocyte groups. In the follicle somewhat protruding a group of lymphocytes nowhere. into the oral cavity shown in Fig. 2, we see such According to INAZAWA, the epithelium of the human lingual radix often contains some taste-buds and OHTOMO says that taste-buds are found on rare occasions 437

2 438 M. KIKUCHI, S. HATAKEYAMA, H. HONMA and D. YAMAGUCHI: Fig. 1. A sagittal section of the radix linguae of a newborn dog. c tonsilar crypt of a lingual tonsil, l lymph nodule, e epithelium, p propria mucosae, g mucous glands, d gland duct, m striated muscle fibres. SETO's impregnation. Fig. 2. A sagittal section of the radix linguae of a newborn dog. l lingual tonsil devoid of lymph nodule, c tonsilar crypt, p proprial plexus, s submucosal plexus, g mucous glands, m striated muscle. Same stain-

3 On the Nerve Supply of the Radix Linguae of Newborn Dog. 439 in the epithelium of the radix linguae of hedgehog too, but such taste-buds were not found in the same part of the tongue of cat and goat. To our interest, we found a rather large number of taste-buds in the root of tongue of our newborn puppy specimen. In Fig. 3 is shown 2 of such taste-buds formed side by side. Fig taste-buds standing side by side in the stratified flat epithelium of the radix linguae of a newborn dog. n a thick sensory fibre entering into the propria mucosae. Same staining. In our specimens, the development of the purely mucous glands is very good. They extend from the submucosa deep into the muscularis, in a manner recalling what has been repoted on such glands in the human radix linguae (Figs. 1 and 2), and their ducts of two-rowed cylindrical epithelium always open out in the follicular crypts (Fig. 1). In the radix linguae of dog thus showing a histological structure considerably resembling that of the radix linguae of man, the incoming sensory nerves originate in the 3rd ramus of the trigeminal nerve, the isthmic branch of the mandibular nerve, the lingual branch of the glossopharyngeal nerve and the pharyngeal branch of the vagal nerve, while the motor nerves originate in the hypoglossal nerve and the sympathetic nerves in the maxillary ganglion. These nerve elements run from the outside into the muscularis and then into the glandular layer forming nerve bundles of varying size, then through the submucosa into the propria mucosae to form the submucosal and the proprial plexus. As found in the radix linguae of man and hedgehog, these bundles form coarse plexus in their courses in the muscularis layer, also in newborn dog. as well as the glandular The prprial and the submucosal plexus consist of thick myelinated sensory fibres and thin unmyelinated vegetative fibres. It is of interest that small nerve cells are found in groups in these plexus (Fig. 4). Ganglia of more numerous nerve cells are found along the nerve bundles forming the plexus in the muscularis and the glandular

4 440 M. KIKUCHI, S. HATAKEYAMA, H. HONMA and D. YAMAGUCHI: Fig. 4. A small ganglion cell group (g) found along the proprial plexus (p) in the radix linguae of a newborn dog. e epithelium. Details in the text. Same staining. Photo layer. These nerve cells have a few very hard-to-stain nerve processes and show the structure as those found by KIKUCHI on the dorsum linguae, clearly indicating that they are of sympathetic nature. The vegetative nerves terminate in terminal reticula as has been always the case in any past study at this laboratory; such terminal reticula were found very notably developed in the glandular layer here. In the proprial plexus in the radix linguae of dog, myelinated sensory fibres are contained in a number smaller than in man but considerably larger than in hedgehog. These sensory fibres emerge from the plexus and form their terminations beneath the epithelium. In newborn dog, these fibres never form such very highly evolved capsulated or uncapsulated corpuscular terminations as found in the human tongue (INAZAWA), or even such end-bulbs as found in this part of goat (YAMA- NOTO et al.), but nearly always in simple branched terminations somewhat more complex than those found in hedgehog (OHTOMO). Not rarely, some end in unbranched terminations. Their stem fibres are mostly of medium size but sometimes very thick and the terminal fibres are either thick and show considerable change in size or thin and show little change in size during their courses and end mostly in sharp points but more rarely in blunt points.

5 On the Nerve Supply of the Radix Linguae of Newborn Dog. 441 Fig. 5. An unbranched sensory termination (n) originated in a medium-sized stem fibre found in a lingual tonsil of a newborn dog. c tonsilar crypt, l lymphocytes gathering. Details in Fig. 6. An unbranched (u) and a bifurcated (b) sensory terminations originated in 2 largersized stem fibres found subepithelially in the radix linguae of a newborn dog. Some of their terminal fibres enter the epithelium (e) to pass over into short intraepithelial fibres.

6 442 M. KIKUCHI, S. HATAKEYAMA, H. HONMA and D. YAMAGUTCHI: In Fig. 5 is shown an unbranched termination formed by a sensory fibre of medium size running into a grouped mass of lymphocytes in a lingual follicle, which upon losing its myelin sheath runs a rather strongly winding course while showing slight change in size at its further end part and ends sharply without ever ramifying. In Fig. 6 is shown an unbranched termination (u) and a bifurcated termination (b) formed by sensory fibres somewhat larger-sized than the above. In these, the terminal fibres show more or less perceptible change in size and some of them run a very short way into the epithelium before ending. It is another intersting finding that such intraepithelial fibres never found in the radix linguae of man, cat, goat or hedgehog are not rare in that of newborn dog. In Fig. 7 is shown a branched termination originating in a medium-sized stem Fig. 7. A simple branched sensory termination formed subepithelially in the radix linguae fibre and comprising 4 or 5 terminal fibres, but in this photo some of the terminal branches are not apparent as desired, being hidden in the proprial connective tissue. These terminal fibres are nearly always thin and show little change in size and some of them again run a little into the epithelium before ending. 3 simple branched terminations formed by a thick and 2 medium-sized fibres are illustrated in Fig. 8. Most of the terminal fibres run not much winding courses while showing moderate change in size and end bluntly or sharply beneath the epithelium. The taste-buds found in the radix linguae are said to be rather scanty, nearly rudimentary and devoid of nerve supply in man (INAZAWA), but in our specimens of newborn dog, these taste buds were often more or less well supplied with sensory fibres, so that it is indubitable that these at least function as gustatory receptors, though utterly uninnervated taste-buds were not absent either as exemplified in Fig. 3. In Fig. 9 is shown a taste-bud found in the thin stratified flat epithelium near

7 On the Nerve Supply of the Radix Linguae of Newborn Dog. 443 Fig. 8. A few simple branched sensory terminations originated in large- or medium-sized stem fibres and found subepithelially in the radix linguae of a newborn dog. e epithelium. Pig. 9. A bifurcated sensory termination supplying a taste-bud (t) found in the epithelium of the radix linguae of a newborn dog. Branch fibres (a and b) somewhat rich in change in the orifice of a follicular crypt. A somewhat more than averagely thick sensory fibre runs toward this taste-bud and then apparently branches out into two rather thick terminal fibres, one of which (a) penetrates a little into the taste-bud, while the other (b) ends near the basis of it, bluntly, respectively. In Fig. 10 is shown another taste-

8 444 M. KIKUCHI, S. HATAKEYAMA, H. HONMA and D. YAMAGUCHI: Fig. 10. Some simple branched sensory terminations found just beneath a taste-bud in the epithelium of the radix linguae of a newborn dog. Their branch fibres showing somewhat change in size arrange plexus-like. Details in the text. Fig rather complex branched sensory terminations found beneath a taste-bud in the epithelium of the radix linguae of a newborn dog. Their branch fibres show conspicuous change in size during their winding courses. Details in the text same staining.

9 On the Nerve Supply of the Radix Linguae of Newborn Dog. 445 bud, which is innervated not by a single sensory fibre as the preceding but by more complex branched trminations formed by some stem fibres in corroboration. The terminal branches show more or less change in size and run conspicuouly winding courses, so that the general arrangement is that of a complex plexus, which stands in a very close contact with the taste-bud. In the photo we see them not clearly enough, but some of the terminal branches run a short way into the gemmal epithelium to end in intra- and extra-gemmal fibres. In Fig. 11 is shown another taste-bud supplied with a rather complex branched termination originating in 2 or 3 thick fibres found in the radix linguae of dog. We regret that this photo shows only one plane and fails in bringing out the complexity of the termination as distinctly as might be desired. In this termination, most of the terminal fibres showed distinct change in size, but none of them formed infra or extragemmal fibres. II. Summary. The radix linguae of newborn dog contains some lingual follicles with varying number of lymphocyte groups such as never found in the tongues of goat and cat. The purely mucous glands in the submucosa of this part are very well developed and are as distributed as in man. It is of interest that the epithelium here in newborn dog is provided with a considerable number of taste-buds. Small groups of sympathetic nerve cells contained in the plexus formed here in the propria and the submucosa. These nerve plexus are made of thin vegetative fibres and a rather large number of thick sensory fibres. The former end as always in STOHR's terminal reticula. The sensory fibres terminate beneath the epithelium in the propria in and near the follicles, either in unbranched or more often in simple branched terminations formed somewhat more complexly than those in hedgehog, but never in corpuscular endings as found in the human radix of the tongue or in end-bulbs as found in this part of goat. The stem fibres are sometimes thick enough, but more frequently medium in size and the terminal fibres are either thick and subject to change in size or thin and mostly end in sharp points. In some cases the the terminal fibres slightly penetrate into the epithelium to form intraepithelial fibres such as never found in the same part of man or any other mammal examined hitherto. The taste-buds in the radix linguae in newborn dog are not such degenerated rudiments as they are in man and some mammals, for some of them have fully developed plexiform terminations formed by several fibres just beneath them and some of the terminal fibres frequently form intra- and extra-gemmal fibres.

10 446 M. KIKUCHI, S. HATAKEYAMA, H. HONMA and D. YAMAGUCHI. References. Abe, Y., Endo a. M. Goto: Sensory innervation of the fore part of dorsum linguae in hedgehog. Tohoku J. exp. Med. 60 (1954). - Inazawa, Y.: Histological studies on the nerves, especially sensory nerves in the human tongue root. Tohoku Igaku Zassi. 42 (1942). - Kamada, Sh.: On the innervation, especially sensory innervation of mucous membrane of the oral cavity of cat. Arch. hist. jap. 8 (1955). - Kikuchi, M.: On the nerve supply of the dorsum linguae and the facies inferior linguae in newborn dog. Ibid. 19 (1990). Nakayama, T.: On intrapithelial nerve fibres in human tongue. Tohoku Igaku Zassi. 33 (1943). - Histological studies on nerves in human tongue papillae, espceially on sensory nerve endings. Ibid. 33 (1943). - On innervation of taste-buds in human tongue. Ibid. 34 (1944). - Ohtomo, N.: Innervation of radical part of tongue of hedgehog. Arch. hist. iap. 7 (1954). - Okano, Sh.: Innervation especially sensory innervation of dog tongue. Tohoku J. exp. Med. 57 (1953). - Yamamoto, T., Y. Ito, H. Ueda a. J. Yamaguchi: Sensory innervation of dorsum linguae in goat. Arch. hist. jap. 13 (1957). - Yamamoto, T., R. Abe, T. Suzuki a. S. Ohta: On the innervation of the posterior part of the tongue in goat. Ibid. 13 (1957).