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APPLIED BIOLOGY 



blood coming back to the heart and collecting for the next "beat" 

 of the ventricle. The extremely thin membrane which incloses the 

 heart is the pericardium (meaning, around the heart). 



FIG. 4. Skeleton of frog viewed from dorsal. Nine segments (vertebrae) 

 and the urostyle (u) in backbone, d, shoulder-blade or scapula, dorsal part 

 of shoulder-girdle ; h, humerus, upper-arm bone ; r, one of two bones in 

 forearm ; i, pelvis ; /, femur or thigh-bone ; t, shank-bone. (From Mar- 

 shall.) 



(D or L) At the anterior end of the heart is a blood-tube (aorta) 

 which branches into two smaller tubes, each of which has several 



