246 THE VASCULAR SYSTEMS 



THE LEFT VENTRICLE 



The left ventricle is longer than the right, and forms the apex 

 of the heart. Its walls are three times as thick as those of the 

 right. Within it presents for examination: 



1. The auriculoventricular orifice, which is smaller than the 

 right and guarded by the mitral or bicuspid valve; and the 

 aortic opening, in front and to the right of the preceding, 

 guarded by the semilunar valves. 



2. The mitral valve is attached, like the tricuspid, on the right 

 side. It consists of two curtains which are larger and thicker 

 than those of the tricuspid, and of two smaller segments, one 

 at each angle of junction of the former. They are furnished 

 with chordae tendinese. 



3. The aortic semilunar valves are similar to but larger and 

 stronger than the pulmonary valves. 



4. Columnos carnece are found as in the right ventricle, and 

 the musculi papillares are very large; one is attached to the 

 anterior wall, the other to the posterior. 



The Endocardium. The inner surface of the heart is lined by 

 a thin membrane, the endocardium, continuous with the inner 

 lining of the great bloodvessels, and helping to form by its 

 folds the various valves. 



Blood and Nerve Supply. The heart is supplied with blood by 

 the coronary arteries, and with nerves by the cardiac plexuses, 

 formed by branches of the pneumogastric and sympathetic 

 nerves. 



The muscle fibers of the heart are attached to cartilaginous 

 rings which surround the auriculoventricular and arterial orifices. 



THE ARTERIES 



There are two great arterial systems (1) the pulmonary, 

 (2) the corporeal. 



THE PULMONARY ARTERIAL SYSTEM 



The pulmonary artery is a short, wide vessel, 2 inches in length. 

 Commencing at the base of the right ventricle, it curves upward 



