Histology and Innervation, Especially, Sensory Innervation of Penis and Urethra in Flying-squirrel

Abstract

The author undertook a study of the histology and the innervation of the penis containing the pars cavernosa urethrae of flying-squirrel using preparations stained with SETO's impregnation.The pars cavernosa urethrae has a broad lumen and many longitudinal mucous folds and is lined by a 2-3-rowed cylindrical epithelium. The corpus cavernosum urethrae surrounding the thin propria of the urethra is made of plexus of very fine veins. The tunica albuginea around it consists in a thin circular layer.No median septum is seen in the corpus cavernosum penis in the corpus penis. This body shows the cross-section of a cap and surrounds the corpus cavernosum urethrae in the proximal part, but more distalwards, it gradually takes an unguinal form in cross-section and ceases to encircle the corpus cavernosum urethrae. The tunica albuginea is very thick and is composed of an inner circular and an outer longitudinal layers. The cavernous body proper is penetrated by trabeculae originating in the tunica albuginea and the caverns lined by one-rowed endothelial cells are formed in the loose connective tissue sparsely stretched between the trabeculae.Neither the epithelium of the glans penis nor that of the inner plate of the praeputium can be macroscopically observed, for the epithelium covering both the parts is represented by one common epithelium as shown in the cross-sections in adult flying-squirrel, just as in man and other animals in fetal stage. Upon approaching the glans penis, the urethral lumen grows narrower and expands lateralwards and the corpus cavernosum penis grows gradually oval in cross-sections.Upon entering the glans penis, the tunica albuginea of the corpus cavernosum urethrae goes out of formation. Going further distalwards, the mucous folds of the urethra become lower, then disappear altogether, the epithelium changes through a thick stratified cylindrical epithelium into a stratified flat epithelium, the lumen grows broader and seems to represent the part of the fossa navicularis in other mammals. The abovementioned common epithelium between the glans and the praeputium originates in this stratified flat epithelium. Between the fossa navicularis and the orificium urethrae externum the lumen is star-formed and the epithelium is a thick stratified flat one.The common epithelium, at the level of the fossa navicularis, surrounds the ossified corpus cavernosum penis, but more proximally, the corpus cavernosum urethrae and the bilaterally drawnout cartilaginous body formed on its ventral side also come within the surrounding common epithelium beside the corpus cavernosum penis. The common epithelium sens out side branches particularly well developed at the level of the fossa navicularis as well as around the cartilaginous body.The body proper of the corpus cavernosum penis, upon entering the glans penis, is taken up by the increasing connective tissue of the tunica albuginea. This connective tissue body is at first oval in cross-sections, then turns circular, shows ossification at the level of the navicularis and becomes a cartilaginous tissue in the proximalmost part.The terminations of the thick and the thin medullated sensory fibres richly contained in the n. dorsalis penis are classifiable by form into several types. First, PACINIan bodies of extremely small size are found in a very small number outside the tunica albuginea of the corpus cavernosum penis.Numerous sensory fibres are found in the pars cavernosa urethrae in flying-squirrel as in man, but none of them end in genital nerve bodies but always in subepithelial and intraepithelial branched terminations. The stem fibre in such a termination, after losing its myelin, branches out into some terminal fibres, which often show change in size in their winding courses and usually end in sharp points and more rarely in blunt points. The ramification of these branched terminations is far simpler than in man.