MORPHOLOGY OF ANIMALS 



the highest reptiles (Crocodilia) the heart is completely 

 divided by a partition into two auricles and two ventricles, 

 and a double circulation, systemic and pulmonary, is 

 established (Fig. 17, C). The blood from the left ventricle 

 goes at once to all parts of the body, whence it returns to 

 the right auricle ; it then falls into the right ventricle and 

 is pumped from that to the lungs; there it is oxygenated 

 and returned to the left auricle, and then from the left 

 ventricle it is again sent out to all parts of the body (Fig. 

 16, C). 



The transformations of the embryonic aortic arches, 

 lying in the pharyngeal walls between the gill-slits, in 

 different classes of vertebrates is shown in Fig. 18 and in 

 the following table : 



A^tl^Arches } ^"°"^^ ^^ ^^"^^ '^^^'' 



The condition of the heart in the embryos and the 

 adults of different classes of vertebrates is summarized in 

 Fig. 17 and in the accompanying table: 



: 53 2 



