824 NBEVOUS SYSTEM OF THE HORSE 



LUMBO-SACRAL PLEXUS 



This plexus (Fig. 576) results substantially from the union of the ventral 

 branches of the last three lumbar and the first two sacral nerves, but it derives a 

 small root from the third lumbar nerve also. The anterior part of the plexus lies 

 in front of the internal iliac artery, between the lumbar transverse processes and the 

 psoas minor. It supplies branches to the ilio-psoas (designated by Girard the 

 iliaco-muscular nerves). The posterior part lies partly upon and partly in the 

 texture of the sacro-sciatic ligament. From the plexus are derived the nerves of the 

 pelvic limb, which are now to be described. 



Femoral Nerve 



The femoral nerve (N. femoralis)^ is derived chiefly from the fourth and fifth 

 lumbar nerves, but commonly, if not always, receives a fasciculus from the third 

 nerve also (Fig. 656). It is the larger of the two nerves which are given off from 

 the anterior part of the lumbo-sacral plexus. It runs ventrally and backward, at 

 first between the psoas major and minor, then crosses the deep face of the tendon 

 of insertion of the latter, and descends under cover of the sartorius over the termi- 

 nal part of the ilio-psoas. It gives off the saphenous nerve, and divides into several 

 terminal branches which dip into the interstice between the rectus femoris and the 

 vastus medialis (Fig. 575). These branches are accompanied by the anterior 

 femoral vessels and innervate the quadriceps femoris. A collateral branch is given 

 off to the ilio-psoas. 



The saphenous nerve (N. saphenus) (Figs. 575, 576, 582) is given off as the 

 femoral crosses the terminal part of the ilio-psoas. It gives off a branch which 

 enters the deep face of the sartorius, and descends with the femoral vessels in the 

 femoral canal. About the middle of the thigh it divides into several branches 

 which emerge from between the sartorius and gracilis, perforate the deep fascia, and 

 ramify on the medial surface and the front of the limb as far downward as the hock. 

 The longer posterior branches accompany the saphenous vessels, while the anterior 

 branches deviate forward toward the stifle and the anterior surface of the leg. 



Obturator Nerve 

 The obturator nerve (N. obturatorius) is derived chiefly from the ventral 

 branches of the fourth and flfth lumbar nerves, but may receive fibers from the 

 third or the sixth (Fig. 656). It runs downward and backward, at first above 

 and then upon the external iliac vein, inclines inward across the obturator vein, and 

 passes through the anterior part of the obturator foramen (Fig. 576). It continues 

 downward through the obturator externus, and divides into several branches which 

 innervate the obturator externus, pectineus, adductor, and gracilis muscles (Fig. 

 581). 



Anterior Gluteal Nerve 



The anterior gluteal nerve (N. glutseus cranialis) is derived chiefly from the 

 last lumbar and first sacral nerves, but commonly has a fifth lumbar root. It 

 divides into four or five branches which emerge through the greater sciatic 

 foramen -i\'ith the divisions of the anterior gluteal artery and supply the glutei, 

 tensor fasciae latae, and capsularis (Fig. 658) . The nerve to the tensor fasciae latse 

 and the anterior part of the superficial gluteus passes between the deep part of the 

 gluteus medius and the gluteus profundus, and is accompanied on the iliacus by 

 branches of the lateral circumflex vessels. 



Posterior Gluteal Nerve 

 The posterior gluteal nerve (N. glutaeus caudalis) is derived mainly from the 

 sacral roots of the lumbo-sacral plexus (Figs. 576, 658) . It divides into two trunks 

 ^ Also termed the anterior crural nerve. 



