COLLATERAL BRANCHES. 1333 



the obturator internus and the gemelli and posterior to the capsular ligament of the hip. 

 Reaching the upper margin of the quadratus femoris it passes anterior to that muscle and 

 terminates in fibres which enter the anterior surface of the muscle for which it is destined. In 

 addition to supplying the quadratus femoris it sends twigs to the gemellus inferior and to the 

 hip joint. 



Variations. The nerve to the quadratus femoris may supply the upper portion of the 

 adductor magnus and may send filaments to the superior gemellus, either as an additional or 

 as a sole supply. 



b. The nerve to the obturator internus has an origin one step lower than that of the 

 preceding nerve, with which it is frequently associated for a short distance. It arises from the 

 anterior aspect of the fifth lumbar and first and second sacral nerves and leaves the pelvis through 

 the great sacro-sciatic foramen, below the pyriformis and the great sciatic nerve and lateral to 

 the pudic nerve and vessels (Fig. 1114). Crossing the spine of the ischium it courses anteriorly 

 through the lesser sacro-sciatic foramen and enters the ischio-rectal fossa, where it terminates by 

 splitting into filaments which enter the posterior surface of the obturator internus. A small 

 branch of this nerve supplies the gemellus superior. 



c. The nerve to the hamstring muscles consists of a bundle of fibres which forms the 

 mesial edge of the gluteal portion of the sciatic nerve. Arising from the anterior aspect of the 

 plexus and deriving its fibres from the fourth and fifth lumbar and first, second and third sacral 

 nerves, it descends in close connection with the sciatic, lying first anterior to the latter and then 

 to the inner side (Fig. 1115). In the thigh the nerve breaks up into two sets of fibres, an 

 upper and a lower. The upper set leaves the sciatic below the tuber ischii and sends fibres to 

 the upper portion of the semitcndinosus and the long head of the biceps femoris. The lower 

 set arises further down in the thigh and funishes twigs to the semimembranosus, the adductor 

 magnus and the lower part of the semitendinosus. 



2. The articular branches are derived from the nerve to the quadratus 

 femoris and sometimes from the anterior aspect of the sciatic. After descending 

 between the capsule of the hip and the gemelli they supply the posterior portion of 

 the capsular ligament of the hip joint. 



The posterior collateral branches comprise, like the anterior, (3) the 

 muscular and (4) the articrdar branches. 



3. The muscular branches include () the nerve to the pyriformis, (b) the 

 superior and (c) the inferior gluteal nerves and (af ) the nerve to the short head 

 of the biceps. 



a. The nerve to the pyriformis may be either single or double. It arises from the dorsal 

 aspect of the second or first and second sacral nerves and enters the anterior surface of its 

 muscle. There may be an additional filament from the root to the superior gluteal nerve con- 

 tributed by the first sacral nerve. 



b. The superior gluteal nerve (n. glutaeus superior) (Fig. 1114) arises by three roots from 

 the dorsal surface of the posterior portion of the lumbo-sacral cord and the first sacral nerve, 

 its fibres being derivatives of the fourth and fifth lumbar and first sacral nerves. After passing 

 above the pyriformis muscle in company with the superior gluteal artery and vein, it leaves the 

 pelvis through the great sacro-sciatic foramen and divides into (aa) a superior and (bb) an 

 inferior branch. 



aa. The superior branch (Fig. 1114) is the smaller of the two, and after passing beneath 

 the glutens medius and along the upper margin of the gluteus minimus reaches and enters the 

 middle of the inner surface of the former muscle, of which it is only the partial nerve supply. 



bb. The inferior branch, larger than the superior, is the continuation of the main trunk. 

 After a forward course between the glutei medius and minimus in company with the lower 

 branch of the deep portion of the superior gluteal artery, it reaches the under surface of the 

 tensor fasciae femoris (Fig. 1114). It supplies the glutei medius and minimus and its terminal 

 fibres constitute the supply of the tensor fasciae femoris. 



c. The inferior gluteal nerve (n. glutaeus inferior) (Fig. 1114) is formed by twigs which arise 

 from the dorsal surface of the posterior part of the lumbo-sacral cord and the first, and some- 

 times the second, sacral nerve. It is frequently fused in the early part of its course with the 

 small sciatic nerve and not infrequently with the nerve to the short head of the biceps. It 

 usually sends a small branch down to join the small sciatic nerve. Passing beneath the pyriformis 

 it emerges from the pelvis into the gluteal region through the great sacro-sciatic foramen, super- 

 ficial to the great sciatic nerve. Immediately upon entering the buttock it breaks up fan-wise 

 into a number of twigs which enter the deep surface of the gluteus maximus about midway 

 between the origin and insertion. 



