288 VERTEBRATE ZOOLOGY 



its hinder end, where it will be seen to be formed by the union of 

 a pair of large arteries, the common iliacs. Trace the branches of 

 one of this pair, but without injuring the white nerve cords which 

 form the lumbosacral plexus. The common iliac is a short trunk 

 which is formed a short space back of its origin by the union of 

 three arteries, of which the largest is the external iliac ; the other 

 two are the internal iliac, or hypogastric,— a smaller artery which 

 passes backward from the dorsal side of the external iliac, sending 

 branches to the bladder, the uterus (in the female), the rectum, 

 the thigh, and the tail,— and the iliolumbar, which arises from the 

 lateral side of the external iliac, opposite the origin of the internal 

 iliac or anterior to it, and passes to the muscles of the body wall 

 and the thigh. The external iliac runs laterally to the body wall, 

 through which it passes after giving off the inferior epigastric, an 

 artery which turns forward, running along the inner surface of the 

 abdominal muscles together with the vein of the same name, and 

 finally anastomosing with the internal mammary artery in the 

 forward part of the body. The continuation of the external iliac 

 is called the femoral artery; with its branches it supplies the 

 greater part of the leg. Follow the femoral and its branches. 



Trace the aorta and its branches from the common iliacs to the 

 diaphragm. As it passes forward from this point it receives the 

 following branches, some of which are paired and some median : 

 the small median sacral artery, which leaves the dorsal surface 

 of the aorta— of which it may be considered the posterior contin- 

 uation—a short distance in front of the common iliacs passing 

 along the ventral surface of the sacrum to the tail; the small 

 lumbar arteries, numbering seven pairs, six of which leave the 

 dorsal surface of the aorta at regular intervals along its course, 

 posterior to the diaphragm, and one of which leaves the median 

 sacral artery,— all going to the muscles of the body wall ; the in- 

 ferior mesenteric, a median artery which leaves the aorta about 

 an inch in front of the common iliacs and carries blood to the colon 

 and the rectum; the spermatic arteries (in the male) and the 

 ovarian arteries (in the female), in each case a pair of vessels 

 which leave the aorta near the inferior mesenteric and may be 

 traced to the scrotum and the ovary respectively ; the renal arteries, 



