Histology and Innervation of the Cloaca and the Penis of Snapping Turtle

Abstract

I wish to call the distalmost part of the end colon of the snapping turtle the anal part of the end colon, since this part, unlike the rectum of mammals, has a histological picture closely resembling that of the so-called anal bladder. Its large lumen suddenly tightens up with the appearance of many longitudinal folds and opens out into the cloaca. This part probably corresponds to the zona columnaris ani in man and other mammals.The crura corporis caverni penis of right and left penetrate far into the lateral sides of the anal part of the end colon and the urethra and show a cavernous communication between the latter organs.On the ventral side of the urethra is found the radix orporis cavernosi urethrae which extends up to the tip of the glans penis. In cross-sections, the corpus is seen in a semilunar form. Many septula running dorsoventrally come out from the tunica albuginea lining the wall of the corpus and a net system of blood vessels is formed in the interstices.The corpora cavernosa penis are well developed near the anal part but lose much in development as they go distalwards along the cloaca. Presently, however, they are seen jutting forcefully into the lumen of the cloaca. A longitudinal narrow furrow runs between the two protruding corpora, which are covered by a mucous membrane in common. These protruding parts form the root part of the so-called glans penis together with the corpus cavernosum urethrae, which is not yet raised out of the cloacal wall in this part, but before long it stands out free from the wall and becomes covered in the same mucous membrane as the corpora cavernosa ponis. The two corpora cavernosa penis come again into mutual communication along the dorsal side of the urethral body, upon entering the glans penis.The corpus cavernosum penis, in particular in its part within the glans penis, contains many trabecular villi of various size sticking out from the tunica albuginea lining the wall of the large cavern running through it. The inner side of the cavern is lined by a single-rowed layer of endotholial cells. The mucous membrane covering the glans penis is composed of a thick stratified cylindrical epithelium and a propria rich in melaniferous fibrocytes.The proximal part of the cloaca is provided with conspicuous longitudinal mucous folds. The epithelium lining it is a stratified cylindrical one, which near the distal end passes over into a flat epithelium without cornification. The propria consists of a fibrous connective tissue and does not contain pigment cells. The tunica muscularis is observable in the vicinity of the anal part of the end colon but gradually fades out in the more distal parts.The innervation of the cloaca in the proximal part where the tunica muscularis is observable is similar to that in the anal part of the end colon. Here, AUERBACH's and MEISSNER's plexuses containing a small quantity of sympathetic nerve cells are formed, though not in strong development, and sensory fibres are also found in a considerable quantity. As the distal parts devoid of a muscularis is approached, the nerve supply becomes weaker. The sensory fibres end in the muscularis and the propria. No intraepithelial fibres have ever been observed here.The sensory terminations formed in the muscularis are of the unbranched and the simple branched types in which the fibres run very peculiar courses of successive loops. The terminal fibres end usually in sharp points. The terminations found in the propria comprise unbranched and simple branched ones in which the fibres run specific winding courses while changing their size.The innervation of the penis shows many interesting points. The vegetative nerves in the corpora cavernosa penis and the corpus cavernosum urethrae originate in the vegetative nerve bundles running along the aa. profundae penis and their branches the aa. corporis cavernosa urethrae. The corpora cavernosa penis