Anat. Labor. of Prof. H. SETO, Tohoku University, On the Histology and Innervation of Rectum and. Anus of Snapping Turtle.

Transcription

1 Arch. hist. jap. Vol. 15, n. 1 (July 1958). P Anat. Labor. of Prof. H. SETO, Tohoku University, Sendai. On the Histology and Innervation of Rectum and Anus of Snapping Turtle. Recently, ABE of this laboratory has succeeded in obtaining many interesting and utterly dependable results in his studies on the fine structure and the innervation of the cloaca and the outer genital organs of the reptile the snapping turtle. As the histology of the various organs, not to speak of their innervation, in reptiles and amphibians, has been left in the dark in most part, the abovecited histological work by ABE is a very valuable one, to say the least. In succession of ABE, the author of this paper also was given the opportunity of studying the histology and the nerve supply of the distal parts of the colon of a male snapping turtle. The materials, fixed for a long time in neutral formol were As in the case of ABE, every one of my preparations was very ideally stained, and upon thorough examination of these, I succeeded in obtaining many interesting findings as follows. I. Individual Findings. ABE has spoken a few words on the histology of the anal part of the rectum in his study, but since this part of the reptile shows a histological picture very complicated and rather widely different from that of man and other mammals, it seems that his description contains a few failures if I may adduce the results of my more detailed examinations in collation. For example, he claims that the anal bladders found on both sides of the end colon are very ill developed, and it seems he had misobserved the urethra in his specimens. The histological picture of the part of male snapping turtle, as reconstructed from my innumerable serial cross sections, was follows, when given in the order starting from the rectum distalwards to the anal part and to the cloaca. The inferior part of the rectum is a tube of 4.5mm diameter, has a rather broad lumen and its mucosa forms 4-5 longitudinal mucous folds. The epithelium here is a smooth-surfaced one-rowed long cylindrical epithelium and has numerous crypts depressed into the propria, a feature of this epithelium distinguishing from that of the anal part described hereunder. These crypts are lined by cubic epithelial cells, which, like the goblet cells in this part of mammals, probably secrete mucus. The propria here is not similar to that in mammals formed of a reticular tissue of 161

2 162 R. MONMA: full of free cells, especially, lymphocytes, but is of fine fibrous connective tissue rich in fibrocytes and contains many blood capillaries in it. The muscularis mucosae is very ill-developed and the submucosa is of loose connective tissue rich in blood vessels. The tunica muscularis is made of an inner circular and an outer longitudinal layers and its surface is lined by a serosa in most part of it (Fig. 1). As details of above, the structure of the rectum of snapping diffe- but in does not show any essential rence from that of mammals, turtle the next anal part, there are many mentionable specificities in the histological picture. The proximalmost part of the anus is somewhat smaller than the rectum, measuring ca. 3mm in diameter, the crypts in the mucosa are observed no more, the lumen is narrowed by formation of a larger number of longitudinal folds and the epithelium is replaced by a stratified cylindrical epithelium, so that the distinction between the rectal and the anal parts is clear at a glance. Now, such changes in the histological structure begin first in the median part of the dorsal side, then gradually pass over the lateral sides, finally to the ventral side. The propria is of a fibrous connective tissue, but unlike in the rectum, aggregates of lymphocytes or lymphonodules are formed here and there, so there are some places formed of reticular tissue. It is very interesting that, unlike in the rectum, the muscularis mucosae is here powerfully developed. The smooth muscle fibres mostly run circularly. Outside the submucosa tunica muscularis consisting of an inner circular and an outer longitudinal layers is observed, as in the rectal part. Going a little more distalwards, the anal part increases to ca mm in diameter and epithelial sacs appear deeply caving into the submucosa on both sides and reaching through the muscularis mucosae down to the surface layer of the tunica muscularis. As exemplified in Fig. 2. A cross section of the proximal part of the anal canal of 4mm in diameter of a snapping turtle. l 1st anal sac on the right side; v the same on the left side. Details in

3 On the Histology and Innervation of Rectum and Anus etc. 163 Fig. 2, a considerably large epithelial sac with longitudinal folds is here found caved into the submucosa on the right side. This sac is connected through a thick haft with the anal canal proper lined by the muscularis mucosae. In the left half of the picture is seen the tangential section of another epithelial sac extending into the submucosa. These sacs are the first pair of anal sacs. Further down at the level of the orificium urethrae internum of the urinary bladder, as shown in Fig. 3, the anal canal decreases in size to ca. 2-3mm in Fig. 3. A cross section of the anal canal at the leavel of the orificium urethrae internum (i) of snapping turtle. s 2nd anal sac, e ductus ejaculatorius, l 1st anal sac on the right side, b epithelium of urinary bladder. Details in the text. Same diameter. No mentionable alteration appears in its fine structure, except that the tunica muscularis is particularly better developed here on the dorso-lateral sides. Besides, at this height, on both sides of the anal canal and somewhat far from its tunica muscularis, rather large sacs of epithelium similar to the anal epithelium become visible; these sacs reach further downwards and finally open out into the anal canal (Fig. 5), that is, they are the second pair of sacs belonging to the anal canal. The ductus ejaculatorii appear in cross-sections on the ventral side of these cacs. Still more distalwards in the anal canal, the considerably large urethra rich in longitudinal folds approaches the anal canal and finally opens out into it on the ventral side (Fig. 4). On this level, the sacs of the second pair as well as the ductus ejaculatorii gradually come nearer to the anal canal. The muscularis mucosae becomes still better developed, and not only passes over into that of the urethra on the ventral side, but also pressing aside the submucosa fuses with the inner circular layer of the tunica muscularis. Thus, in the vicinity of the outer orifice of the

4 164 R. MONMA: urethra, the development of the smooth muscle tissue becomes quite more remarkable. Fig. 4. A cross section of the anal canal at the level of the orificium urethrae externum of a snapping turtle. u urethra, s 2nd anal sac, e ductus ejaculatorius. Fig. 5. A cross section of the anal canal a little farther caudal to the urethral opening. A 2nd pair of the anal sacs (s) opens out into the anal duct, e ductus ejaculatorius, p corpus cavernosum penis on the left side. Details in the text. Same

5 On the Histology and Innervation of Rectum and Anus etc. 165 A little farther caudal to this urethral opening, the anal canal undergoes a very abrupt change. The anal canal increases in size to ca. 4.5mm, its lumen broadens, the folds becomes even better developed and the second pair of the anal sacs opens out into the anal duct, as shown in Fig. 5. The ductus ejaculatorii also approach the muscularies of the lateral side. It is of deep interest that the proximal part of the corpus cavernosum penis makes appearance on the ventro-lateral side of the anal canal at this level. Fig. 6. A cross section through the anal canal of 5.5mm in diameter of a snapping turtle. e ductus ejaculatorius running through the tunica, muscularis, p corpus caver- Still further downwards, the anal canal begins to swell further to ca. 5.5mm in diameter and the lumen attains the maximum breadth (Fig. 6). The ductus ejaculatorii run gradually into the muscularies on both sides, which, however, loses a little in development at this level and further downwards it goes on becoming worse developed. The ductus ejaculatorii enter the propria on either side, run to the ridge of a pair of large folds standing out of the mucosa on the ventral side into the lumen and open out into the anal canal there (Fig. 7). A third large mucous fold protrudes from the dorsal side. At this level, the corpora cavernosa penis become now fully developed. Going further down beyond the openings of the ductus ejacutatorii, the anal canal is slowly reduced in size, till its diameter becomes only 2-3mm. The mucous folds consist here in small narrow ones and the narrow lumen lies amidst them showing the cross-section reminding those of the FALLOPIan tube. At this level, a spongy body probably corresponding to the corpus cavernosum urethrae appears on the ventral side. What is of high interest, epithelial sacs or canals lined by an epithelium similar to that of the anal canal begin with a blind end at the central part of the spongy body in a pair, which, when followed up in the cross-sections,

6 166 R. MONMA: Fig 7. Across section of the anal canal of a snapping turtle at the level of the openings of the ductus ejaculatorii. Small ductus ejaculatorii on both sides are contained in the heads of 2 ventral long mucous folds (v), d dorsal large mucous fold. Details in soon unite into a single canal and then it runs toward the dorsal side of the cavernous body (Fig. 8). Further down, it begins to assume the form similar to the anal canal with a narrow lumen amidst long and narrow folds, then comes into full communi- Fig. 8. A cross section of the distal part of the anal canal (a) of ca. 3mm in diameter of a snapping turtle. u corpus cavernosum urethrae, t 3rd anal sacs

7 On the Histology and Innervation of Rectum and Anus etc. 167 cation with the anal canal on its dorsal side as shown in Fig. 9 and finally opens out into the cloaca. ABE has taken this canal to represent the urethra, but this is nothing but the third pair of sacs of the anal canal fused in one. Fig. 9. A cross section of the anal canal of a snapping turtle at the level of the communication between the anal canal (a) and the united single canal of the 3rd anal sacs (t), u corpus cavernosum urethrae. p corpus cavernosum penis. Details in the text. Photo Many works have been reported from this laboratory on the innervation, especially, the sensory innervation of the rectum and the anus of man and mammals, but none of them was concerned with reptiles, except that by ABE, who has achieved many interesting results in his study on the sensory innervation of the outer genitals and the cloaca of a male snapping turtle. The preesnt-author also could obtain many new informations on the innervation, especially sensory innervation, of the inferior rectum and the anal part of a male snapping turtle as reported below. These findings of mine I will describe in comparison with the findings on the same part of man and mammals by the above-cited predecessors and those on the cloaca of snapping turtle by ABE, in the following. Between the outer and the inner layers of the tunica muscularis of the rectum of snapping turtle, I found AUBERBACH's plexus as was found in the rectum of man and mammals, but the ganglia in it were very ill developed, the small number of ganglion cells therein having only 2-3 processes at most or being quite apolar. This plexus is essentially of sympathetic nature and the nerve fibres are composed of thin fibres. In the nerve bundles coming through the mesorectum, however, not a small number of thick sensory fibres may be found beside such fine vegetative fibres. MEISSNER's plexus closely related to the AUERBACH's plexus is formed in the submucosa of the rectum too, but this is even worse developed than the AUERBACH's plexus above, nearly no nerve cell, being contained in it. The fine

8 168 R. MONMA:

9 On the Histology and Innervation of Rectum and Anus etc. 169 vegetative nerve fibres originating in any of these AUERBACH's and MEISSNER's plexuses finally come into formation of STOHR's terminal reticula in snapping turtle's rectum too and they spread out in the tunica, muscularis and also in the submucosa and the mucosa. The incoming sensory fibres end sometimes in unbranched and simple branched snake-like terminations showing very peculiar winding courses in the muscularis or spreading thence into the submucosa (Fig. 10), and sometimes in unbranched and simple branched terminations in the vicinity of the crypts after running into the propria and without branching or sending out 2-3 terminal branches which usually run wavy courses and end in sharp points. These sensory terminations generally originate in thick fibres, but those originating in thin fibres are not rare either. In Fig. 11 is shown an unbranched sensory termination originating in a thick fibre, which shows change in size in its wavy course and ends sharply, found in the basal part of crypt, while in Fig. 12 we see 2 unbranched terminations similarly ending in sharp points, which originate in moderately thick fibres and of which the one on the right side describes 2 loops in its course while the other on the left side Fig unbranched sensory terminations found near the basis of a crypt in the distal part of the rectum of a snapping turtle, of which the one on the right side

10 170 R. MONMA: Fig. 13. A bifurcated sensory termination found near the basis of a crypt in the caudal part of the rectum of a snapping turtle. shows no mentionable winding throughout. Fig. 13 shows a bifurcated sensory termination of a fine fibre, with its terminal fibres running wavy courses before ending sharply in the basal part of a crypt. As described above, sensory terminations are not rarely found particularly in the mucous membrane of the inferior part of the rectum of snapping turtle, as much in the counterpart of man (SETO) and mammals (YOKOYAMA, YAMAMOTO, SHIMODA, NIIZUMA et al.). Their terminal fibres mostly end around the crypts, but none of them enter their epithelium to form intraepithelial fibres, in turtle as well as in man and mammals. Besides, these are more simply formed in this reptile than the same in man and mammals. Upon passing from the rectum into the proximal end part of the anus, the AUERBACH's plexus and the MEISSNER's plexus are still in formation, even in better development than in the rectum, the MEISSNER's plexus here often containing ganglion cells. This better development of the plexus is in keeping with the far better development of the lamina muscularis mucosae here than in the rectum. The sensory fibres in this part are also much more numerous than in the distal part of the rectum, but their terminal formation is not much different,

11 On the Histology and Innervation of Rectum and Anus etc. 171 unbranched and simple branched terminations being only found subepithelially. For example, in Figs. 14 and 15 are shown loop-like and snake-like terminations of Fig. 14. A loop-like unbranched sensory termination found in the propria mucosae of the proximal part of the anal canal of a snapping Fig. 15. A snake-like unbranched sensory termination found in the propria of a mucous fold in the proximal part of the anal canal of a snapping turtle. u a fine unbranched sensory termination ending sharply beneath simple type both found in the propria of different mucous folds in the proximal part of the anus. In man (SETO) and mammals (YAMAMOTO, SHIMODA, YOKO- YAMA and NIIZUMA), intraepithelial fibres are found in abundance in this part,

12 172 R. MONMA: but I could not find intraepithelial fibres in the stratified cylindrical epithelium in this part of the reptile I studied. In the narrowest part of the anus at the height of the orificium urethrae internum, the lamina muscularis mucosae is still better developed, thickening to a small distance to the tunica muscularis, so that the submucosa is pressed down to an extreme thinness and the AUERBACH's and MEISSNER's plexuses are permitted to develop luxuriantly while the sensory fibres also grow considerably larger in number than in the proximal part. The terminations of these sensory fibres consist in comparatively complex loop-like endings in the muscularis mucosae, beside a rather large number of subepithelial unbranched and simple branched terminations similar to those in the proximal anal part above (Fig. 16). More rarely, I found Fig. 16. A bifurcated sensory termination found in the propria mucorae in the narrowest part of the anal canal of a snspping turtle at the hight of the orificium urethrae internum. Details in the text. Same staining. branched terminations composed of several strands of terminal fibres, but no intraepithelial fibres were demonstrated here either. In the still more distal part where the urethra has its outer opening into the anal canal, the sensory fibres gain even more in number than the AUERBACH's and MEISSNER's plexuses gain in development. The sensery fibres here too usually penetrate into the mucous folds and end subepithelially in unbranched and simple branched terminations, while some loop-like terminations are found in the muscularis here too, as in the more proximal In the part a little parts above. below the level where the second pair of anal sacs open out into the anal canal, that is, in the part where the anal canal attains the largest diameter, many nerve bundles are found running in accompanying the thick blood vessels entering the anal wall on the dorsolateral sides (Figs. 6 and 7). These nerve bundles pass over into the AUERBACH's plexus formed in the muscularis here

13 On the Histology and Innervation of Rectum and Anus etc. 173 arranged somewhat irregularly and the MEISSNER's plexus formed in the submucosa. The latter plexus is considerably well developed in the ventral side and contain rather large ganglia. In this part, the sensory fibres increase still further, and such simple branched terminations of fibres running very complex looped courses as shown in Fig. 17 are found in many places of the submucosa rich in connective Fig. 17. Unbranched and simple branched sensory terminations, fibres of which run complex looped courses, found in the submucosa of the anal canal of a snapping turtle at the level of its largest diameter. Same tissue. The number of the sensory fibres running into the propria and forming comparatively complex branched teminations grows also considerably larger. So, in this part, we may find branched terminations even more complex in formation than in the more proximal parts. In Fig. 18 is shown a somewhat complex branched termination found in the subepithelial propria on the ventro-lateral side of the anal canal here. Its stem fibre is a thick one and its many terminal fibres, showing change in size in their frequently winding courses, end all in sharp points. In my specimens, however, I found no such intraepithelial fibres as found in this part of man and mammls here either. Fig. 19 shows 2 bifurcated terminations also found in the propria of the ventro-lateral side, the teminal fibres of which run frankly looped courses while showing change in size and end sharply. AUERBACH's and MEISSNER's plexusese are still in good development in the

14 174 R. MONMA: Fig. 18. A comparatively complex branched sensory termination found in the propria mucosae of the anal canal at the level of its largest dia- Fig bifurcated sensory termiations, fibres of which run complex looped courses and show change in size, found in the propria mucosae of the anal canal distal part of the anal canal, but the ganglia in them are poorer in formation. The sensory fibres also slowly decrease as the cloaca is approached, but the snake-like terminations in the muscularis are still in frepuent formation (Fig. 20). Unbranched and simple branched terminations are chiefly formed in the mucosa, more complex

15 On the Histology and Innervation of Rectum and Anus etc. 175 Fig. 20. A looped unbranched sensory termination formed in the inner layer of the tunica muscularis of the distal part of the anal canal of a snapping turtle. Same staining. branched terminations now being extremely rare. It is, however, very interesting that here uncapsulated glomerular terminations of small type are not at all rare in the propria of this part. For example, in Fig. 21 we see beside two unbranched Fgi unbranched sensory terminations consisting in thin fibres and an uncapsulated glomerular sensory termination of small type found in the propria on the dorsal side of the distal part of the anal canal of terminations a simple glomerular termination found in the propria on the dorsal side of the anal canal. Its terminal fibres consist in medium -sized fibres showing little change in their courses. In Fig. 22 is shown a somewhat complex glomerular termination found subepithelially on a lateral side of the anal canal, consisting of fine fibres and thick fibres showing change in size.

16 176 R. MONMA: The distal part of the anal canal of the reptile is the part essentially corresponding to the zona intermedia ani of man and mammals. Consequently, it seems natural that in this part of snapping turtle, there should be found such glomerular terminations, for in the corresponding part of man and mammals, it is known that glomerular type genital nerve bodies are frequently in existence (SETO et al.) In the last place, I may point out that subepithelial sensory terminations are found in the anal sacs too, although in quantity much smaller than those in the anal canal proper and of much simpler formation limited to the unbranched and simple branched type. No intraepithelial fibres were ever found in these sacs either. As described above, the sensory fibres in the rectum and the anus of snapping turtle consist in thick smooth-surfaced fibres and have terminations of the same type as in the cloaca and the penis of the same reptile as reported by ABE. Only the terminations in the anal part of the distalmost colon, however, are generally more complex in form and more numerous in quantity than those in the cloacal wall. Fig. 22. An uncapsulated somewhat complex glomerular sensory termination found in the propria on a lateral side of the distalmost part of the anal II. Summary. The author has studied the histology and the innervation of the region between the lower part of the rectum and the cloaca of a male snapping turtle using preparations stained with SETO's impregnation. The distal part of the rectum measures 4.5mm in diameter and several longitudinal mucous folds protrude into the rather spacious lumen, which is lined by a one-rowed cylindrical epithelium and crypts are formed in the propria. These crypts are lined by a one-rowed cubic epithelium probably of mucous nature. The

17 On the Histology and Innervation of Rectum and Anus etc. muscularis mucossae is very ill-developed, and the tunica musclaris here is composed of an inner circular and an outer longitudinal layers. The proximalmost portion of the anal part is 3mm in diameter, has no crypts in the mucosa, the epithelium is of a stratified cylindrical epithelium, and lymphonodules are found scattered in the propria. The muscularis mucosae is markedly well developed, and the tunica muscularis is similar to that in the rectum. In the part a little more distal, the anal canal enlarges to 4-4.5mm in diameter and the first pair of anal sacs formed by depression of the epithelium makes appearance in the submucosa on both the lateral sides. Going a little more distalwards to the level of the orificium urethrae internum, the anal canal narrows down to 2-3mm in diameter, the tunica muscularis becomes particularly well developed on the ventro-lateral sides, and the second pair of anal sacs comes into view on both the lateral sides extending even beyond the tunica muscularis. The ductus ejaculatroii are found running on their ventral side. Upon going further caudalwards, at the height of the orificium urethrae externum, the second pair of sacs as well as the ductus ejaculatorii come nearer to the anal canal. The muscularis mucosae is here further better developed. A little further downwards, the anal canal enlarges to 4.5mm in diameter, its lumen is broaden and the longitudinal folds grow larger. The second pair of sacs open out here into the anal canal and the proximal part of the corpus cavernosum penis comes into view on the ventro-lateral sides on this level. On the level a little further below, the anal canal attains the largest diameter of 5.5mm. The ductus ejaculatorii enter the tunica muscularis on both the lateral sides and soon open out on the ridge of a pair of large folds standing out from the mucosa on the ventral side. Another large mucous fold protrudes from the dorsomedian part of the mucosa. The anal canal loses in size further distalwards, narrowing down to 2-3mm. It is provided with many small narrow folds in this part and the lumen is narrowed down. A spongy body that must correspond to the corpus cavernosum urethrae of mammals appears now on the ventral side. A pair of blind canals is formed in the central part of that body. More dorsal to the spongy body, these two canals unite into one, which runs more caudalwards and finally commnnicates with the anal canal, then opens out into the cloaca. These blind canals represent the third pair of anal sacs. The AUERBACH's plexus in the tunica muscularis is very poor in development in the lower part of the rectum, and the incoming nerve fibres consist in fine vegetative fibres and a small number of thick sensory fibres. The MEISSNER's plexus formed also in the submucosa here is even worse developed than the AUER- BACH's plexus. The vegetative fibres here too end always woven into STOHR's terminal reticula. The sensory fibres coming into the rectum sometimes end in unbranched and simple branched snake-like terminations in the muscularis or spreading thence further into the submucosa, but otherwise also run further into the propria and form unbranched and simple branched terminations there. The latter have terminal fibres running wavy courses and end sharply in the vicinity of the rectal crypts. As in the same part of mammals, intraepithelial fibres are not found here.

18 178 R. MONMA: The AUERBACH's and the MEISSNER's plexus are found in the cranialmost part of the anal canal too, in better development here than in the rectum. Here the number of sensory fibres is also much larger, but their terminal formation is similar to that in the rectum. No such intraepithelial fibres as found in the corresponding part of man and mammals could be found in my specimens. At the height of the orificium urethrae internum, or the narrowest part of the anal canal, the AUERBACH's and the MEISSNER's plexus are further better developed and the sensory fibres reincrease in number. Beside unbranched and branched terminations, somewhat more complex branched terminations are also often found subepithelially. At the height of the orificium urethrae externum, the above plexuses are indeed well developed, but the further increase of sensory fibres is even more remarkable. The sensory terminations here, however, are similar to those in the preceding part. On a level a little lower than that where the second pair of the anal sacs opens out into the anal canal, or in the part where the anal canal attains the largest diameter, many nerve bundles come in from the dorsolateral side and pass over into the AUERBACH's and MEISSNER's plexus formed in this part. Ganglia of considerable size are found in the latter plexus. The sensory fibres increase yet further and simple branched looped terminations are found in the submucosa and the propria, respectively, particularly in the lateral side. The AUERBACH's and the MEISSNER's plexus are still in formation in the distalmost part of the anal canal, but their development here is considerably lowered. The sensory fibres are decreased as the cloaca approached, but in the muscularis are still fonnd snake-like terminations and in the mucosa appear some unbranched and simple branched terminations. It is of interest here, however, that uncapsulated glomerular terminations may be found not rarely in the propria. These many be comparable with the genital nerve bodies found in the zona intermedia ani in man and mammals. The anal sacs of the first, second and third pairs all contain some subepithelial sensory terminations, but their number is much smaller and their terminal mode is simpler than in the anal canal proper.

19 On the Histology and Innervation of Rectum and Anus etc. 179 References. Abe, R.: Histology and innervation of the cloaca and the penis of snapping turtle. Arch. hist. jap. 10 (1956). - Izumi, I.: On the innervation, especially, the sensory innervation, especially, the sensory innervation of anus in human adults. Arch. hist. jap. 9 (1955). - Kakazu, Sh.: On innervation, especially, sensory innervation of rectum and anus in canine fetus. Arch. hist. jap. 13 (1957). - Niizuma, Sh.: Histological study on the innervation of rectum and anus of bat. Arch. hist. jap. 9 (1956). - Niizuma, Sh., K. Nozaki, M. Komatsu a. T. Numata: On sensory innervation of zona cutanea ani in bat. Arch. hist. jap. 9 (1955). - Seto, H.: Uber die intraepithelialen Nerven beim Nenschen. II. Die afferenten Nervenendigungen im Analepthel, nebst einigen Bemerkungen uber den histologischen Feinbau der epithelialen Analgebilde. Arb. Anat. Inst. Sendai. 23 (1940). -On sensory innervation of caudal part of rectum in human adult. Okajimas Fol. anat. jap. 28 (1956). - Shimoda, M.: Innervation, especially, sensory innervation of caudal part of rectum and mucous part of anus of dog. Arch. hist. jap. 7 (1954). - Yokoyama, T.: Innervation, especially, sensory innervation of rectum and anus in cat. Arch. hist. jap. 12 (1957).