826 NERVOUS SYSTEM OF THE HOESE 



the trochanter major and the tuber ischii over the gemellus, the tendon of the 

 obturator internus, and the quadratus femoris. In its descent in the thigh it lies 

 between the biceps femoris laterally and the adductor, semimembranosus, and 

 semitendinosus medially, and is continued between the two heads of the gastroc- 

 nemius as the tibial nerve. Its chief branches are as follows: 



1. In the pelvic part of its course the sciatic nerve supplies small muscular 

 branches to the obturator internus, gemellus, and quadratus femoris; the branch 

 to the obturator internus reaches the muscle by passing through the anterior end 

 of the lesser sciatic foramen. 



These very small nerves arise from the upper border or deep face of the great sciatic, about 

 haK way between the two sciatic foramina. The nerve to the obturator internus Ues along the 

 dorsal margin of the sciatic and divides into branches for both heads of the muscle. The nerves 

 to the gemellus and quadratus femoris commonly arise from the deep face of the sciatic by a com- 

 mon trunk which passes back between the latter and the sacro-sciatic ligament to the posterior 

 border of the gluteus profundus, where it divides. 



2. As the sciatic nerve turns down behind the hip joint it gives off a large 

 muscular branch (Ramus muscularis proximalis), which divides to supply the 

 semimembranosus and the short heads of the biceps femoris and semitendinosus. 



3. The posterior cutaneous nerve of the leg or external saphenous nerve (N. 

 cutaneus sura; caudalis) is detached from the sciatic about the middle of the thigh. 

 It receives a fasciculus from the peroneal nerve and descends with the recurrent 

 tarsal vein on the lateral face of the. gastrocnemius to the distal third of the leg. 

 Here it perforates the deep fascia and ramifies under the skin on the lateral surface 

 of the tarsus and metatarsus (Fig. 657). 



4. The peroneal nerve (N. peronajus) (Figs. 580, 585, 659)^ is a large trunk 

 which arises from the great sciatic nerve very shortly after the latter emerges from 

 the pelvic cavity. It descends with the parent trunk to the origin of the gastroc- 

 nemius; here the peroneal nerve deviates outward and forward across the lateral 

 face of the gastrocnemius under cover of the biceps femoris, and divides at the 

 origin of the lateral extensor muscle into superficial and deep branches. The 

 collateral branches include one to the biceps femoris, the reinforcing fasciculus 

 detached about the middle of the thigh to the posterior cutaneous nerve, and, 

 lower down, the lateral cutaneous nerve of the leg (Ramus cutaneus surse later- 

 alis).^ The latter emerges between the middle and posterior divisions of the 

 biceps femoris at the level of the stifle joint and ramifies under the skin. The 

 superficial peroneal nerve (N. peroneeus superficialis)^ furnishes branches to the 

 lateral extensor, and descends in the furrow between that muscle and the long 

 extensor, perforates the deep fascia of the leg, and ramifies under the skin on the 

 front and the lateral face of the tarsus and metatarsus. The deep peroneal nerve 

 (N. peroneeus profundus)^ is the direct continuation in point of size of the peroneal 

 trunk. It dips in between the lateral and long extensors of the digit, gives branches 

 to these muscles and the tibialis anterior, and descends in front of the intermuscular 

 septum which separates the two muscles first named. It continues downward 

 behind the tendon of the long extensor and divides on the front of the hock into 

 medial and lateral branches. The medial branch (Ramus medialis) passes down 

 under the skin on the anterior face of the metatarsus and supplies the cutaneous 

 fibers of this region. The lateral branch (Ramus lateralis) furnishes a twig to the 

 extensor brevis muscle and descends with the great metatarsal artery. It supplies 

 the skin on the lateral face of the metatarsus and the fetlock. 



In the greater part of its course in the leg the deep peroneal nerve is separated from the 

 anterior tibial vessels by the tibialis anterior. It should be noted that the lateral one of the two 



' Also known as the external popliteal nerve. 

 2 Also termed the peroneal cutaneous nerve. 

 ' Also termed the musculo-cutaneous nerve. 

 * Also termed the anterior tibial nerve. 



