142 



BIOLOGY: GENERAL AND MEDICAL 



aquatic is abandoned for the terrestrial mode of life. 

 During embryonal life the circulation is carried on 

 much as it is in the fishes, the branchial arches being 

 conspicuous, but upon the attainment of adult life, and 

 the establishment of a pulmonary circulation the bran- 



FIG. 53. Diagram of the heart and branchial arches in a, reptile. Position 

 and lettering as in preceding figures. Lv, left ventricle; r.v, right ventricle 

 (Galloway.) 



chial arteries atrophy and true pulmonary circulation 

 takes its place. 



The frog affords an excellent example of the batrachian 

 type of circulation. The heart is distinctly three-cham- 

 bered, having one ventricle and two completely separated 

 auricles. The blood discharged by the ventricle passes 



