CEREBRO-SPINAL NERVES 403 



size formed by fibres from the fourth and fifth lumbar roots, and in part 

 also from the loop between the third and fourth. Descending between 

 the psoas magnus and parvus, it passes downwards at the outer side of 

 the external iliac artery under cover of the sartorius, and after crossing 

 the conjoined tendon of the psoas and iliacus muscles, ends in a number 

 of branches, which pass between the vastus internus and rectus femoris 

 to be distributed to the extensors of the legs. 



It gives off" the internal saphenous nerve, and sends branches to the 

 rectus femoris. 



3. The Obturator Nerve i« situated beneath the peritoneum on the 

 inner side of the pelvis, and follows the course of the artery of the same 

 name through the obturator foramen to the internal aspect of the thigh. 

 It is derived from the fourth and fifth lumbar roots, and gives branches to 

 the obturator externus, adductors of the thigh, the pectineus and gracilis 

 muscles. 



4. The Anterior and Posterior Gluteal Nerves, also called the 



small sciatic nerves. These nerves leave the pelvis by the great sciatic 

 notch. The anterior gluteal consists of four or five branches, which are 

 distributed to the gluteus medius, the tensor vagina femoris, vastus ex- 

 ternus and internus, and the gluteus externus. The posterior gluteal nerve 

 is represented by two branches — a superior and inferior. The superior 

 supplies the superficial gluteus, the middle gluteus, and the biceps femoris. 

 The inferior branch, after passing over the outer side of the tuber ischii, is 

 destined to the skin of the thigh, the semitendinosus, and with a branch of 

 the internal pudic nerve to the structures of the perineum. 



The Great Sciatic Nerve is the largest in the body. It rs derived 

 from the lumbo-sacral plexus, and issues from the great sciatic opening 

 as a broad white band; thence it takes a downward course between the 

 sacro-sciatic ligament and the gluteus maximus. On reaching the thigh 

 it is lodged between the biceps femoris and semitendinosus, having the 

 semimembranosus and great adductor of the thigh supporting it within. 



On nearing the leg it passes between the two heads of the gastrocnemius 

 muscle, when it takes the name of the internal popliteal nerve. This is 

 continued on as the posterior tibial, which dividing, forms the internal and 

 external plantar nerves. In its course down the limb it supplies a slender 

 branch to the obturator internus, pyriformis, gemelli, and quadratus femoris. 



The External Popliteal Nerve is a branch of considerable size given 

 off" from the great sciatic near to the gemini muscles. It then passes 

 downward and forward between the biceps femoris and the outer head of 

 the gastrocnemius. On reaching the outer lateral ligament of the stifle 

 it divides into the musculo-cutaneous nerve and the anterior tibial. 



