MAMMALIA 



445 



small intestine near its anterior end. The small intestine is 

 very much shorter in flesh-eating animals than in the vegetable 

 feeders. At the junction of the small and large intestine there 

 is a blind pouch or sac (c&cum, vermiform appendix) which 

 is large in the Herbivora, but in man it is a mere rudiment. It 

 is doubtful whether it has any function in the human race. 

 It is often the seat of serious inflammation. 



FIG. 236. 



FIG. 236. Diagram of the heart and chief vessels in the mammals, ao., aorta; a./., left auricle; 

 o.r., right auricle; c, carotid artery; d.a., dorsal artery; p.a., pulmonary artery; p.v., pulmonary 

 vein; s, subclavian artery; v.c., venae cavae (pre-caval and post-caval); v.l. t left ventricle; v.r., right 

 ventricle. 



Questions on the figure. What kind of vessels communicate with the auricles? 

 What with the ventricles? What is the position of the valves? Trace the direc- 

 tion of the blood flow in the various parts of the blood vessels figured. What is 

 the distribution of the veins and arteries shown here, i.e., to what organs do their 

 minuter branches go? 



458. Circulatory System. Mammals are warm blooded, but with lower tem- 

 perature than is found among the birds. It ranges from 35 to 40 C. The heart 

 is completely four-chambered as in birds, the left side containing pure blood and 

 the right impure (Fig. 236). The aorta, arising from the left ventricle, has only 

 one arch the left, whereas only the right is found in birds. The general compari- 

 son of the conditions in vertebrates may be seen from the table on page 343. There 

 is an hepatic-portal, but no renal-portal, circulation. 



The lymphatic vessels are an important part of the circulatory apparatus in 

 all vertebrates. Under the pressure that exists in the arteries, some of the fluid 

 portion of the blood finds its way through the walls of the capillaries into the spaces 

 among the tissues. This cannot get back into the veins, and hence it is desirable 

 that special vessels be provided to get it back into the circulation. Starting with 



