THE METABOLIC MACHINERY OF ANIMALS 



307 



pericardium, the inner lining of which covers the heart and secretes 

 the pericardial fluid in which the organ lies. The heart of an adult 

 mammal may be divided into a right and left side, each having no 

 direct internal connection with the other. Each half may likewise 



innomlnatfi- left, 

 ar-tery.... subclavian 



; arterx.^ 



pLdmonory 

 artery. 



Superior" 



.bicuspid. 



inferior- 

 vsna casid} 



tricuspicC- 

 vctlve 



dnorduojs. 

 tancunaxa. 



right 

 ventricle 



papillar/ 

 muscle^ 



. left, . 1 

 — -vetttncle 



A section through the mammalian heart. Read the text carefully and trace 

 the course of blood through the heart. 



be divided transversely into an upper relatively thin-walled auricle 

 and a more muscular lower ventricle. The right side contains 

 unoxygenated or venous blood, while the left auricle and ventricle 

 contain arterial blood saturated with oxygen. 



The right auricle receives the venous blood by two vessels known 

 as the superior vena cava, or precava, entering on the anterior surface 

 and bringing the blood from the head and neck, and the inferior vena 

 cava, or postcava, which empties into the lower portion of the right 

 auricle, returning the blood from parts of the body below the dia- 

 phragm. The blood passes into the right ventricle through the; 

 tricuspid valve which, as the name suggests, is composed of three 

 irregularly shaped flaps. The tips of these flaps project into the 



