828 NERVOUS SYSTEM OF THE HORSE 
and radiate to supply that muscle, the popliteus, the soleus, and the flexors of the 
digit. Small cutaneous twigs are also detached along the course of the nerve. 
PLANTAR NERVES 
The plantar nerves, medial and lateral (N. plantaris medialis, lateralis), 
result from the bifurcation of the tibial nerve in the distal part of the leg (Figs. 
583, 584). They continue at first in the same direction and relations as the parent 
trunk, in direct apposition and enclosed in a common sheath. At the hock they 
diverge at a very acute angle and descend in the tarsal canal behind the deep flexor 
tendon in company with the plantar arteries. The medial plantar nerve supplies 
cutaneous nerves to the medial aspect of the tarsus and metatarsus, descends along 
the medial border of the flexor tendons behind the superficial plantar metatarsal 
vessels, and is otherwise arranged like the corresponding volar nerve of the fore- 
limb. The lateral plantar nerve deviates outward between the two flexor tendons 
to reach their lateral border. It supplies a branch to the suspensory ligament, and 
in its further course resembles the corresponding nerve of the fore limb. 
In so-called ‘‘tibial’’ neurectomy the operator really cuts the two plantar nerves which have 
not yet separated. The anastomotic branch between the two plantar nerves is smaller and more 
distal than that which connects the corresponding nerves of the fore limb, and is absent in 30 per 
cent. of the cases according to Rudert. 
SACRAL NERVES 
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. 657). 
The fifth anastomoses with the dorsal branch of the first coceygeal 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 pelvie plexus. The first and second are the largest, and unite with 
ach 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 pudie and posterior hemorrhoidal nerves. 
The pudic nerve (N. pudendus) (Figs. 576, 580, 658) passes downward and 
backward partly embedded in the sacro-sciatic ligament, then 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 penis and the penile layer of the prepuce. 
Within the pelvis it anastomoses with the posterior hemorrhoidal nerve, and gives 
branches to the bladder and urethra, the terminal part of the rectum, and the skin 
and muscles of the anus (Fig. 577). It also supplies the nerve to the ischio-caverno- 
sus muscle and numerous branches to the corpus cavernosum of the penis and 
urethra. In the female it terminates in the clitoris and vulva (Fig. 578). 
The posterior hemorrhoidal nerve (N. hemorrhoidalis caudalis) passes down- 
ward and backward above the pudice nerve, with which it anastomoses. It gives 
twigs to the terminal part of the rectum, the sphincter ani externus, and the sur- 
rounding skin (Fig. 577). In the female it supplies twigs to the vulva also (Fig. 
578). 
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. 
