Histological Study on the Innervation of Scrotum and Perineum in Human Adult

Abstract

The scrotum, being favoured with much more remarkable formation of papillae than in other haired skin, is richly provided with sensory nerve fibres. The presence of smooth muscle layer indicates development of vegetative nerves. As the perineum also shows a histological picture similar to that of the scrotum, it also belongs to the skin of external genitals. The innervation is accordingly similar to that of scrotum.In the subcutaneous tissue of the scrotum and perineum, the scrotal and perineal plexus are formed. These consist of medullated sensory and non-medullated vegetative fibres. The latter form mainly in the smooth muscle layer, but partly in the papillae, their termination that is the terminal reticulum (STOHR).In the scrotum, as in the common haired skin, neither intraepithelial fibres nor PACINIAN corpuscles are found.The sensory terminations found in scrotum are classified into the three types of simple unbranched and branched terminations, plexus-like terminations and genital nerve corpuscles. The simple unbranched and branched terminations are far larger in number than in general haired skin, occurring in papillae in particular. The irregular branched terminations found in the muscle layer of the male papilla mammae (SUGA) are not observed in scrotum.Plexus-like terminations are found in scrotum only in a small number. Their terminal formation consists in, that two or three medullated fibres run into papillae, and after loss of the myelin, undergo repeated ramification to show a plexus-like arrangement. But in rare cases, the glomerular terminations also come forth, but since they lack the connective tissue capsule, they are easily distinguished from the genital bodies.In scrotum, there are found many genital bodies mainly in the papillae. partly in the papillar layer, though not so numerous and large as in glans penis and glans clitoridis. All of them belong to YAMADA's type I and type II, his type III being not observed here.The type I is represented by the glomerular formation of sensory fibres, which after loss of the myelin, run into capsulated inner bulb and extend over the entire inside of the inner bulb, to form glomerular arrangement by repeated branching and anastomosis. By the type II, the central. part of inner bulb alone is taken up by the comparatively simple branched terminations of nerve fibres, leavieg a clear peripheral zone filled with inner bulb substance. The inner bulb of these genital bodies shows the syncytial nature consisting of minute granular basic substance and oval special nuclei. They are deemed to be derived from the SCHWANN's sheath.In the perineum also, neither intraepithelial fibres nor PACINIAN bodies are found. The sensory terminations in papillar layer are of three types as in scrotum. But the frequency of distribution is somewhat different from that in scrotum. The number of simple unbranched and branched terminations is larger, while the genital bodies are smaller in number as well as in size than in scrotum.The presence of genital bodies in the perineum clearly shows that this area belongs to the skin of external genitals. These bodies also belong only to YAMADA's type I and type II. The former are found in the papillae, the latter mainly in the papillar layer.The pubes are of much stronger development than the common downy hairs. But, as the terminal area of sensory hair nerves is here represented mainly by the SETO's hair nerve shield, their terminal formation is in general rather simple, that is represented by simple plexus like terminations. Their development is a little lower than by the hairs of head, and far lower than by eyelashes and hairs in pars cutanea of lip, but more or less stronger than by common downy hairs.