706 NERVOUS SYSTEM OF THE HORSE 



small root from the third liiml)ar 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. 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 (or anterior crural) nerve (N. femoralis) is derived chiefly from 

 the fourth and fifth lumbar nerves, but commonly receives a fasciculus from the 

 third nerve also (Fig. 524). It is the larger of the two nerves which are given off 

 from the anterior part of the luml:)o-sacral plexus. It runs backward at first be- 

 tween the psoas major and minor, then crosses the deep face of the tendon of in- 

 sertion of the latter, and descends under cover of the sartorius in the furrow between 

 the two heads of the iliacus. It gives off the saphenous nerve, crosses the lower 

 part of the outer head of the iliacus, and divides into several branches which dip 

 into the interstice between the rectus femoris and the vastus internus (Fig. 450). 

 These branches are accompanied by the anterior femoral vessels and innervate the 

 quadriceps femoris. Collateral muscular branches are supplied to the ilio-psoas 

 and sartorius. 



The saphenous nerve (N. saphenus) (Figs. 450, 451, 457) is given off as the 

 parent trunk crosses the furrow between the psoas major and the outer head of 

 the iliacus. It descends with the femoral vessels in the femoral canal, and gives 

 branches to the sartorius, gracilis, and pectineus. 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 inner 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 

 This nerve (N. obturatorius) is derived from the ventral branches of the last 

 three lumbar nerves (Fig. 524). It runs downward and backward, at first above 

 and then u]ion the external iliac vein, inclines inward across the obturator vein, 

 and passes through the anterior part of the ol^turator foramen in front of that vessel 

 (Fig. 451). It continues downward through the obturator externus, and divides 

 into several branches which innervate the obturator externus, pectineus, adductor, 

 and gracilis muscles (Fig. 456). 



Anterior Gluteal Nerve 

 This nerve (N. glutseus cranialis) is derived chiefly from the last lumbar and 

 first sacral nerves. It divides into four or five branches which emerge through the 

 great sacro-sciatic foramen with the divisions of the anterior gluteal artery and 

 supply the gluteal and tensor fasciae lata? muscles. The nerve to the latter and 

 the anterior part of the superficial gluteus passes between the deep part of the glu- 

 teus medius and the deep gluteal muscle, and is accompanied on the iliacus by 

 branches of the external circumflex vessels. 



Posterior Gluteal Nerve 

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

 sacral roots of the lumljo-sacral plexus (Figs. 451, 526). It divides into two trunks 

 which emerge above the great sciatic nerve. The upper nerve passes Inickward 

 on the sacro-sciatic ligament and divides into branches which enter the two heads 

 of the biceps femoris; it supplies a branch to the posterior part of the middle gluteus, 

 and a nerve which turns around the posterior border of the latter and enters the 



