THE LOWER LIMB 435 



border of the pyriformis it gives a branch to the gemellus superior, 

 which enters that muscle on its deep surface near the upper border, 

 close to the origin. 



Nerve to Quadratus Femoris. — This nerve arises from the sacral 

 plexus, more particularly from the ventral divisions of the descend- 

 ing branch of the fourth lumbar, the fifth lumbar, and the first sacral 

 nerves. It passes through the lower compartment of the great 

 sacro -sciatic foramen, below the pyriformis, where it lies in close 

 contact with the deep surface of the great sciatic nerve. It then 

 passes, in succession, beneath the gemellus superior, obturator 

 intemus, gemellus inferior, and quadratus femoris, entering the 

 last muscle on its anterior or deep surface near the upper border, 

 close to the origin. As it passes beneath the gemellus inferior, it 

 parts with its branch to that muscle, which enters its deep surface 

 near the upper border, close to the origin. 



The nerve to the quadratus femoris also supplies, as a rule, an 

 articular branch to the back of the hip- joint. 



Lymphatics. — ^The superficial lymphatics of the gluteal region 

 terminate in the inguinal glands (superior or oblique superficial 

 inguinal glands). Tiie deep lymphatics enter the pelvis, and 

 terminate in the internal iliac glands. 



For the great and small sacro-sciatic ligaments see the description 

 of the pelvis in Abdomen Section. 



THE TfflGH 



Back of the Thigh and Popliteal Space. 



Landmarks. — The hamstring muscles give rise to a prominence 

 along the back of the thigh, but they cannot be individually 

 recognised until they reach the popliteal space. The great sciatic 

 nerve is deeply placed, being under cover of the long or ischial 

 head of the biceps femoris, but its course may be indicated by 

 drawing a line from the centre of the back of the knee-joint to a 

 point between the great trochanter and the tuber ischii, rather 

 nearer the latter than the former. The upper two-thirds of this 

 line correspond with the great sciatic nerve, and the lower third 

 with the internal popliteal ner\'e. 



The situation of the popliteal space behind the knee-joint is 

 indicated by a depression when the joint is flexed. The strong 

 tendon of the biceps femoris can be felt on the outer side, as it 

 descends to reach the head of the fibula, and in front of it the 

 long external lateral hgament of the knee-joint can be distinguished 

 by its tense, cord-like feel. Anterior to this ligament the lower 

 part of the ilio-tibial band of the fascia lata may be felt. The 

 external popliteal nerve is close to the inner side of the biceps 

 tendon. Lower down it can be felt just below the head of the fibula. 

 On the inner side of the pophteal space, over the back of the inner 



