ANATOMY OF THE HEART AND BLOOD-VESSELS 295 



little cartilaginous nodule, the corpus Arantii, and on each side of 

 this the edge of the valve is very thin and when it meets its neigh- 

 bor turns up against it and so secures the closure. 



The Arterial System. All the arteries of the Body arise either 

 directly or indirectly from the aorta or pulmonary artery, and the 



Sd 



Mpl 



Mpm 



FIG. 105. The left ventricle and the commencement of the aorta laid open. 

 Mpm, Mpl, the papillary muscles. From their upper ends are seen the cordce 

 tendinece proceeding to the edges of the flaps of the mitral valve. The opening 

 into the auricle lies between these flaps. At the beginning of the aorta are seen its 

 three pouch-like semilunar valves. 



great majority of them from the former vessel. The pulmonary 

 artery only carries blood to the lungs, to undergo exchanges with 

 the air in them after it has circulated through the Body generally. 

 After making its arch the aorta continues back through the 

 chest, giving off many branches on its way. Piercing the dia- 



