208 THE HUMAN BODY. 



part smooth, but from each a hollow pouch, the auricular 

 appendage, projects over the base of the corresponding ven- 

 tricle as seen at Adx and As in Figs. 79 and 80. These 

 pouches have somewhat the shape of a dog's ear and have- 

 given their name to the whole auricle. Their interior is 

 roughened by muscular elevations, covered by endocardium, 

 known as the fleshy columns (columnw carnece). On the 

 inside of the ventricles (Fig. 81) similar fleshy columns are 

 very prominent. 



The Auriculo-Ventricular Valves. These are known 

 as rigid and left, or as the tricuspicl and mitral valves re- 

 spectively. The mitral valve (Fig. 81) consists of, t \zo_flaps 

 of the endocardium fixed by their bases to the margins of 

 auriculo-ventricular aperture and with their edges hanging 

 down into the ventricle when the heart is empty. These- 

 unattached edges are not however free, Tjir^have fixed to 

 them a number of stout connective-tissue corc|s, the?j&r(7 

 tendinew, wlricjb^are fixed below to muscular elevations, the 



and Mpl, on the interior of the- 



ventricle. The cords are long enough to let the valve flaps 

 rise into a horizontal position and so close the opening be- 

 tween auricle and ventricle which lies between them, and 

 passes up behind the opened aorta, Sp, represented in th& 

 figure. The tricuspid valve is like tho mitral but with 

 three flaps instead of two. 



Semilunar Valves. These are six in number: threejit 

 the mouth of the aorta, Fig. 81, and three, qnif-.fi ^jfrfi them y 

 afTEe" month oT the^j^ulmonary artery. Each is a strong: 

 crescentic pouch fixed by its mofe^urved border, and with 

 its free edge turned away from the heart. When the- 

 valves are in action these free edges meet across the vessel 

 and prevent blood from flowing back infa fli 



In the middle of the free border of each valve is a little- 

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

 this the edge of the valve is very thin and w^hen it meets 

 its neighbor doubles 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 pulmo- 

 nary artery and the great majority of them from the for- 



