1 86 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



nary artery, back into the corresponding lung. With the loss 

 of gills in the amphibia and their absence in the higher groups, 

 the lungs become the chief respiratory organs, and the proximal 



Fig. 199. Aortic arches of Amblystoma embryo, after a reconstruction by 

 Dr. F. D. Lambert, aa 1-°, afferent arteries ; b, balancer ; ba, extremity of bul- 

 bus arteriosus; c, common carotid; da, dorsal aorta; e *-^, efferent arteries; h, 

 hyoid arch :/, jugular vein; ra, radix aortse; v, vein from balancer to jugular; ~^a, 

 ventral aorla ; 1-5, places where gill clefts are to form. Notice that the second 

 aortic arch is lackine. 



