VI 



STRUCTURE OF HEART 



87 



Thus the blood is driven by the heart to the various 

 parts of the body through the efferent arteries, and is 

 returned from the various parts of the body to the heart 

 by the afferent veins. Two questions thus naturally 

 arise : how is it that the blood takes this direction and 



sysl.tr 



FIG. 22. The heart of the Frog from the ventral aspect, with the cavities laid open. 

 (X6.) 



V. v. aiirir.ujo-ventrirulnr valves ; 



entricle. (From Parker and Haswell's Zoology.) 



not the other, and how does it make its way from the 

 artery of a given organ into the vein ? 



Internal Structure of the Heart. To answer the first 

 question why the blood leaves the heart by the arteries 



