THE HIND EXTREMITY. 265 



The gluteal artery, immediately after its origin, passes 

 through the foramen situated between the posterior margin 

 of the ilium and the anterior margin of the sacro- sciatic 

 ligament. It then breaks up, sending large branches to 

 the gluteal muscles, and among others a remarkable one 

 running along the lateral margin of the sacrum between 

 two folds of the ligament. Thus the muscles on the quarter 

 are supplied with blood. 



The lateral sacral artery passes from the terminal por- 

 tion of the internal iliac in a backward direction along the 

 outer margin of the under surface of the sacrum ; thus the 

 artery tends to approach its fellow. It terminates poste- 

 riorly in giving origin to vessels running to the tail {lateral 

 coccygeal arteries). Superiorly it gives off small hrancJies 

 to the spinal cord, which pass through the subsacral fora- 

 mina and medullary arteries to the sacral hones. Inferiorly 

 it gives off hcemorrhoidal branches to the rectum, w^hich 

 anteriorly anastomose with the terminal branches of the 

 posterior mesenteric, posteriorly with the artery of the bulb 

 and its branches. 



The middle sacral when present runs along the central 

 line of the under surface of the sacrum, and terminates in 

 giving rise to the middle or hiferior coccygeal artery. 



The femoral vein exactly corresponds to the femoral 

 artery ; just above the trochanter minor internus it receives 

 the vena saphena (which we have already seen coursing 

 along the inner surface of the limb from the hock, subcu- 

 taneously placed). Also in front of symphysis pubis it 

 receives the transverse branch already noticed. It termi- 

 nates superiorly in forming the external iliac vein, which 

 unites with the internal iliac vein (which brings blood 

 from the parts supplied by the artery of the same name) 

 to form the common iliac vein, a vessel of about three 

 inches in length, which combines with its fellow under the 

 last lumbar vertebra, above the posterior aorta, to form 

 the commencement of posterior vena cava. This vessel 

 receives the circumflex vein of the ilium ; it is to be found 

 between the external and internal iliac arteries. The pos- 

 terior extremity is supplied by four large nerves in addi- 

 tion to small sacral branches and the sympathetic system ; 

 these are the crural, gluteal, sciatic, and obturator. 



Like all the other spinal nerves, those in the lumbar 

 region, on emerging from the spinal canal through the 



