356 NERVOUS SYSTEM. 



down, in company with the vena saphena, distributing twigs to 

 the skin covering the inward and anterior part of the thigh and 

 leg, where it often sphts into two branches, and is traceable with 

 the vein as low as the fetlock. 



The obturator nerve, contributed to by the third, but 

 principally formed by the fourth lumbar nerve, sweeps round the 

 brim of the pelvis, first above, afterwards to the inner side of, the 

 external iliac artery, and passes through the anterior nook of the 

 foramen magnum ischii, detaciiing some twigs to the obturator 

 muscles in its passage, and is subsequently found sunk in the 

 haunch, behind the pectineus, but before the short and longheads 

 of the triceps; to which muscles it gives branches, and after- 

 wards creeps under the gracilis, upon whose inner surface it 

 spreads and expends its ultimate filaments. 



The gluteal nerve receives a tributary filament from the 

 last lumbar, but owes its formation principally to the first sacral 

 nerve. It leaves the cavity of the pelvis through the foramen in 

 the anterior part of the sacro-sciatic ligament, and winds round 

 upon the dorsum ilii, in company with the gluteal artery, and is 

 entirely expended in the substance of the gluteus maximus. 



The sciatic nerve, the largest in the body, derived from 

 the union of the last of the lumbar with the three anterior of the 

 sacral nerves, immediately after its formation quits the cavity of 

 the pelvis, through a hole in the anterior part of the sacro-sciatic 

 ligament, proceeds backward in contact with that ligament, 

 passes between the hip-joint and the tuberosity of the ischium, 

 and plunges deep into the substance of the haunch. Here we 

 find it split into three large branches — the popliteal nerves — 

 which are lodged in an inter-muscular hollow, imbedded in adi- 

 pose membrane, having the semitendinosus and semi-membra- 

 nosus posteriorly, the biceps to the outward side, and the large 

 head of the triceps to the inward side : in passing through the 

 foramen it detaches three or four branches to the head of the 

 biceps, about the same number to the semitendinosus, and two 

 or three to the semimembranosus. Of the three large nerves into 

 which the trunk divides — Thejirst and principal one takes an 

 oblique course between the bellies of the gastrocnemii, leaves 

 those muscles at the place where they become tendinous, and 

 runs to the hock between their tendons and the muscles of the 

 deep posterior crural region, clinging to the faschia enveloping 

 the latter. At the hock it separates into two nerves— the inter- 

 nal and external metatarsal nerves : the former runs over the 

 tendon of the flexor pedis, and upon the leg creeps along the in- 

 ner and anterior border of the flexor tendons ; the latter passes 

 between the tendon and the base of the os calcis, and pursues a 



