824 NERVOUS 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 fifth 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. glutieus 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 with the divisions of the anterior gluteal artery and supply the glutei, 
tensor fasci latee, and capsularis (Fig. 658). The nerve to the tensor fascize late 
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. gluteus caudalis) is derived mainly from the 
sacral roots of the lumbo-sacral plexus (Figs. 576, 658). It divides into two trunks 
1 Also termed the anterior crural nerve. 
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