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 hmb, 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 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 hsemorrhoidal 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 hsemorrhoidal 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 hsemorrhoidal nerve (N. hsemorrhoidalis caudalis) passes down- 

 ward and backward aljove the pudic 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- 

 coccygcus ventralis lateralis and the skin of the root of the tail and joins the first 

 coccygeal nerve. 



