Five pairs of =sacral nerves= (Nn. sacrales) are present in the horse.
The small =dorsal branches= emerge through the dorsal sacral foramina
and the space between the sacrum and the first coccygeal vertebra, and
ramify in the muscles and skin of the sacral region and the adjacent
part of the tail (Fig. 525). The fifth anastomoses with the dorsal
branch of the first coccygeal nerve.
The =ventral branches= leave the vertebral canal through the ventral
sacral foramina and the interval between the sacrum and first coccygeal
vertebra. They are connected with the sympathetic by rami communicantes,
and contribute branches to the pelvic plexus. The first and second are
the largest, and unite with each other and with those of the last three
lumbar nerves to form the lumbo-sacral plexus. The third and fourth are
connected with each other, and the majority of their fibers go to form
the pudic and posterior hæmorrhoidal nerves.
The =pudic nerve= (N. pudendus) (Figs. 451, 455, 526) accompanies the
internal pudic artery to the ischial arch, turns around the latter,
parting company with the artery, and pursues a flexuous course along the
dorsum penis as the =nervus dorsalis penis= and ramifies in the glans
and the penile layer of the prepuce. Within the pelvis it anastomoses
with the posterior hæmorrhoidal nerve, and gives branches to the bladder
and urethra, the terminal part of the rectum, and the skin and muscles
of the anus (Fig. 452). It also supplies the nerve to the
ischio-cavernosus muscle and numerous branches to the corpus cavernosum
and corpus spongiosum. In the female it terminates in the clitoris and
vulva (Fig. 453).
The =posterior hæmorrhoidal nerve= (N. hæmorrhoidalis caudalis) passes
downward and backward above the pudic nerve, with which it anastomoses.
It gives twigs to the terminal part of the rectum, the sphincter ani
externus, and the surrounding skin (Fig. 452). In the female it supplies
twigs to the vulva also (Fig. 453).
The ventral branch of the fifth nerve is small. It gives twigs to the
sacro-coccygeus ventralis lateralis and the skin of the root of the tail
and joins the first coccygeal nerve.