COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 26; 



voluted, and pass laterally to the ovaries. In its passage along the mid-dorsa 

 line the aorta gives off paired lumbar arteries at segmental intervals. Thest 

 are found by loosening the aorta and looking on its dorsal surface. Posterioi 

 to the genital arteries the inferior mesenteric arises as an unpaired visceral brand 

 and passes to the descending colon and rectum, running in the mesocolon. Ii 

 the mesocolon it forks into the left colic artery passing craniad along the descend 

 ing colon and the superior hemorrhoidal artery passing caudad to the posterio: 

 part of the descending colon and the rectum. 



Add these vessels to the drawing of the aorta. 



The digestive tract may now be removed and discarded, leaving the end o 

 the large intestine in place. Hold the stump of the colon together with thi 

 urinary bladder and in female specimens the uterus (the forked coiled tube a 

 the posterior end of the peritoneal cavity) back against the pubes and follow thi 

 aorta farther. Near the end of the peritoneal cavity it forks into the two commoi 

 iliac arteries in the rabbit; in the cat it gives off a pair of external iliac arterie: 

 followed shortly by a pair of internal iliac arteries. Anterior to this place ii 

 the cat, or in the rabbit at the level of the fork or from the common iliac arteries 

 a pair of iliolumbar arteries arises and passes laterally along the body wall 

 The iliolumbar artery divides into an anterior branch, which passes forwarc 

 toward the kidney, and a posterior branch, which extends to the thigh. 



The two common iliac arteries in the rabbit soon fork into an anterior externa 

 iliac and a posterior internal iliac. In the cat the external and internal iliac: 

 arise separately from the aorta, the latter immediately posterior to the former 

 After giving rise to the iliacs the aorta continues in the mid-dorsal line as thi 

 small median sacral or caudal artery, lying halfway between the two interna 

 iliacs. In the cat this vessel arises from the fork of the internal iliacs. In thi 

 rabbit it springs anterior to the forking of the aorta, from the dorsal surface o 

 the latter; its origin is concealed by the postcaval vein and will be seen later 

 The sacral artery supplies the sacral region and the tail. 



Follow the external iliac. It passes laterocaudad out of the peritonea 

 cavity, in the rabbit to the dorsal side of the inguinal ligament. As it passe 

 through the abdominal wall or shortly beyond the wall it gives rise to the dee\ 

 femoral artery (cat) or the inferior epigastric (rabbit). In the cat this vesse 

 gives off branches into the thigh, while these are lacking in the rabbit. In botl 

 animals the following branches are present : branches into the mass of fat betweei 

 the thighs and into the external genital organs, of which one branch, in mal 

 specimens, constitutes the external spermatic artery; and the main vessel then 

 as the inferior epigastric artery, turns craniad and ascends in the abdomma 

 wall, running along the inner surface of the rectus abdominis muscle. It anas 

 tomoses with the superior epigastric artery. In the rabbit there arises, eithe 

 from the inferior epigastric at the origin of the latter from the external iliac o 

 from the external iliac itself near by, the superficial epigastric artery which extend 



