THE VASCULAR SYSTEM 99 



Carefully clear away the tissues in which the inferior 

 vena cava is imbedded and find the lumbar veins , which 

 join the dorsal side of the inferior vena cava. Note their 

 number, position, and distribution. 



Exercise XXV. Make a full-page drawing of the veins anterior 

 and posterior to the heart, incorporating the sketch required by 

 Exercise XIV. 



ARTERIES POSTERIOR TO THE HEART 



The descending aorta is the posterior continuation of the 

 aortic arch. It courses caudally through the thorax and 

 abdomen, ventral to the vertebral column, carrying blood 

 to the body walls, viscera, hind limbs, etc. Its position and 

 conspicuous size make its identification easy. The main 

 branches are as follows, beginning at the anterior end of 

 the series. 



The paired intercostal arteries pass dorsally from the 

 thoracic section of the aorta to the muscles between the ribs. 

 Determine the number, arrangement, and distribution of 

 these arteries. 



The first large artery leaving the dorsal aorta after it 

 enters the abdominal cavity is the coeliac. Passing ven- 

 trally, this divides into three branches: the splenic, the 

 hepatic, and left gastric arteries. The splenic artery splits 

 into several branches which terminate in the spleen. It 

 sends smaller rami to the pancreas and stomach. The he- 

 patic artery, some distance from its origin, delivers blood to 

 the following branches. The right gastric artery goes to 

 the region of the pylorus, thence along the lesser curvature 

 of the stomach, and anastomoses with the left gastric ar- 

 tery, which is described below. The right gastro-epiploic 

 artery passes to the greater curvature of the stomach. 

 The superior pancreatico-duodenal artery courses along the 



