COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 265 



destroyed in removing the skin; it anastomoses with the external mammary, a 

 tributary of the long thoracic. The external iliac passes to the dorsal side of 

 the inguinal ligament, and as the femoral vein continues along the medial side 

 of the leg in company with the femoral artery. Follow the internal iliacs. 

 After a short distance the sacral or caudal vein enters one of them, usually the 

 left one; it accompanies the caudal artery. Caudad of this, each internal iliac 

 receives the middle haemorrhoidal vein which ascends from the anus and lies 

 along the side of the rectum. The tributaries of the internal iliac cannot be 

 followed farther conveniently; they come chiefly from the gluteal region. 



Draw the branches of the postcaval, adding them to the drawing previously 

 made. The iliacs and postcaval may then be removed and the origin of the 

 caudal artery from the aorta traced. 



Cat: The postcaval is formed dorsal to the forking of the aorta by the union 

 of the two large common iliac veins. One of them, usually the left one, receives 

 the small sacral or caudal vein which lies parallel to the artery of the same name. 

 About one inch posterior to its junction with the postcaval each common iliac 

 is formed by the union of the internal iliac {hypogastric) and the external iliac. 

 The former receives branches from the gluteal region and receives the middle 

 haemorrhoidal vein, which runs along the sides of the rectum from the anus 

 forward, and also collects from the bladder. The external iliac passes out of 

 the abdominal cavity. At the place of exit it receives on its medial side the 

 deep femoral vein, which collects from the thigh, from the fat between the thigh, 

 from the external genital region (receiving in males the external spermatic vein 

 from the testes), and also receives the inferior epigastric vein from the inner 

 surface of the rectus abdominis muscle. The branches from the thigh may 

 enter the external iliac separately. The external iliac, now known as the femoral 

 vein, passes along the thigh, receiving branches from the leg muscles. For these 

 consult R and J. 



Draw these branches as far as found, adding them to the drawing of the post- 

 caval vein previously made. 



8. The structure of the heart. — Remove the heart from the body, cutting 

 across the bases of the great vessels. Identify the systemic veins entering the 

 right auricle (three in the rabbit, two in the cat) and the pulmonary veins enter- 

 ing the left auricle. Cut into the wall of each auricle by a transverse slit and 

 wash out the clotted blood which generally fills the interior. Note the thick 

 ridged walls of the auricular appendages and the thinner smoother walls of the 

 remainder of the auricle. Note the inter auricular septum extending dorsally 

 between the two auricles and completely separating them. Find the large 

 auriculo~ventricular openings in the floor of the auricles. In the cat find near 

 the dorsal edge of the interauricular septum the opening of the coronary sinus 

 into the right auricle, noting the valve— the valve of the coronary sinus— -which 

 guards the opening. The coronary sinus is the remnant of the original left 



