360 



METAZOAN PHYLA 



A moist skin may, under certain conditions and in certain types of 

 amphibians, serve also for respiration. Generally speaking, how- 





iw 



Carotid \ 

 artery 

 to head 



J-^-- 



Dorsa/ 

 aorta 



Carotid 



Pu/monary 

 etrtery 



B 



Dorsal aorta 



Pulmonary 

 Carotid artery artery 



Capillary rv 

 System ^ 



Ventral 

 aorta 



Left aortic 

 arch 



Carotid" 

 artery 



Subclav- 

 ian 



artery 

 to fore 

 leg 



Aortic 

 arch 



Pulmonary arts, 

 Righ f aortic arch 



Aorta 



Carotid 

 artery 



\ Subclav-y 



' , ian . 



artery 



, to -^ 



^ I fore leg \ 



Pulmonary 

 artery 



Aorta 



F G H 



Fig. 245. — Diagrams showing steps in the changes in the branchial arches accompany- 

 ing the development of lung breathing. A, the primitive or embryonic condition; B and D, 

 the condition in fishes, D being a lateral view; C and E, tailed amphibian, E being again 

 a lateral view; F, a reptile (lizard) ; G, a bird; //, a mammal. The corresponding arches are 

 numbered in roman numerals. Vessels which have disappeared are indicated by dashes. 

 (Based upon Wiedersheim and Parker, "Elements of the Comparative Anatomy of Verte- 

 brates.") 



ever, terrestrial amphibians have acquired lungs, which are paired 

 sacs developed from the ventral side of the pharynx, by means of which 

 they take oxygen directly from the air. This is a second adaptive 



