710 NERVOUS SYSTEM OF THE HORSE 



ligament, and in its further course resembles the corresponding nerve of the 



fore limb. 



In so-called "til)ial" neurectomy the operator reall}^ cuts the two phmtar nerves which 

 have not yet separated. The anastomotic branch between the two plantar nerves is smaller 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. 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 luml)ar 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. 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 ])enis 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 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. 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 hsemorrhoidal nerve (N. haemorrhoidalis caudalis) passes down- 

 ward and backward above the putlic 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. 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. 



Coccygeal Nerves 



The coccygeal nerves (Nn. coccygei) commonly number five pairs. Their 

 dorsal and ventral branches anastomose to form respectively two trunks on either 

 side, which extend to the tip of the tail and supply its muscular and cutaneous 

 nerves. The dorsal trunk runs with the dorso-lateral artery between the sacro- 

 coccygeus dorsalis and intertransversales muscles (Fig. 454). The ventral trunk 

 accompanies the ventro-lateral artery below the intertransversales. 



The Sympathetic Nervous System ^ 



The S3nnpathetic nervous system (Systema nervorum sympathicum) is that 

 part of the nervous system which serves (1) to transmit stimuli to the heart-muscle, 

 unstriped muscle, and glands; (2) to conduct impulses from the viscera to the cere- 

 brospinal system. 



Many of the fibers are dei'ived from the cerebrospinal system and are rearranged and dis- 

 tributed in the sympathetic system. Numerous sympathetic fibers arc contributed to the cerebro- 



' The special statements of tliis description refer to the system of the horse. A few important 

 difTcrential features will be mentioned in the account of the nervous system of the other animals. 



