The morphological aspects of the innervation of the external urethral striated sphincter.

Innervation of the sphincter urethrae externus muscle was studied in 30 human fetuses with the aid of operation microscope. The investigated muscle receives direct branch from anterior roots of S2, S3, or S4, or from the trunk of the pudendal nerve. The branch to the muscle divides into 2 or 3 rami before it enters the muscle, or it divides into 2 or 3 terminal rami, and gives off the dorsal nerve of the penis or clitoris.