" MAMMALIA. 



435 



function in the human race, 

 inflammation. 



It is often the seat of serious 



447. Circulatory System. Mammals are warm blooded, but with lower 

 temperature 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. 233). The aorta, arising from the 

 left ventricle, has only one arch the left, whereas only the right is found 



FIG. 233. 



s 



v.c. 



v.c.-- 



-do, 



FIG. 233. Diagram of the heart and chief vessels in the mammals, ao., aorta; a.l., 

 left auricle; a.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., 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 direction 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? 



in birds. The general comparison of the conditions in vertebrates may 

 be seen from the table on page 340. 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 the irregular spaces in the 

 tissues, in which the lymph collects, we find vessels less regular than the 



