THE LOWER LIMB 433 



and gluteus maximus, and is distributed over the back of the cocc5nc. 

 The inferior gluteal branch enters the deep surface of the gluteus 

 maximus with the inferior gluteal ner\"e, and it anastomoses in 

 the muscle with the superficial division of the gluteal artery. The 

 muscular branches are distributed to the adjacent external rotator 

 muscles and the origins of the hamstrings. In the latter muscles 

 an anastomosis takes place with the external terminal branch of 

 the obturator artery. 



The anastomotic branches are two in number. One passes to 

 the digital fossa, where it anastomoses with the gluteal, ascending 

 branch of the internal circumflex, and first perforating arteries. 

 The other passes to the interval between the quadratus femoris and 

 adductor magnus, where it anastomoses with the transverse branch 

 of the internal circumflex, the transverse branch of the external 

 circumflex, and the first perforating arteries, This fourfold anasto- 

 mosis is called the crucial anastomosis. 



The articular branches are two or three in number. They pass 

 beneath the gemelli and obturator internus with the nerve to the 

 quadratus femoris, and pierce the back part of the capsular ligament 

 of the hip- joint. 



The gluteal cutaneous branches pass round the lower border of 

 the gluteus maximus with the gluteal cutaneous branches of the 

 small sciatic nerve, and are distributed to the integument over the 

 lower part of the muscle. 



The comes nervi ischiadici is a long branch which descends 

 for some distance with the great sciatic nerve, to which it is dis- 

 tributed, and in which it anastomoses with the perforating branches 

 of the arteria profunda femoris. After ligature of the femoral 

 artery in the upper third of the thigh this branch becomes much 

 enlarged. 



The place of emergence of the sciatic artery from the pelvis is 

 indicated as follows : draw a line from the posterior superior iliac 

 spine to the outer border of the tuber ischii, and take a point in 

 this line at the junction of the middle with the lower third. 



The sciatic vein terminates in the internal iliac vein. 



The sciatic artery in the early embryo is the leading arterial trunk of the 

 lower limb. As the femoral artery is developed it forms a junction with the 

 sciatic in the neighbourhood of the knee, and so becomes the chief artery, 

 and the part of the primitive sciatic between the knee and the gluteal region 

 for the most part disappears. 



Internal Pudic Artery. — ^This vessel arises from the anterior 

 division of the internal iliac, and at first Hes within the pelvic 

 cavity. It is only the second part of the vessel which is seen in the 

 gluteal region, and which will be described here. Having emerged 

 from the pelvis through the lower compartment of the great sacro- 

 sciatic foramen below the pyriformis, the artery passes downwards 

 for a short distance, and crosses over the back of the spine of the 

 ischium. It then courses through the small sacro-sciatic foramen, 

 and is lost to view. 



28 



