218 



THE HUMAN BODY. 



nous nodule, the corpus Arantii, and on each side of this the 

 edge of the valve is very thin and when it meets its neighbor 

 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 great majority of them from the former vessel. 



Mpl 



Mprn 



FIG. 92. 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. 



The pulmonary artery only carries blood to the lungs, to un- 

 dergo 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 



