366 



METAZOAN PHYLA 



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

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



-a 



WlS 



Carotid 

 artery^ 



Carotid 

 artery 

 to fiead 



Dorsa/ 

 aorta 



Pu/monary 

 a/rfery 



B 



Pulmonary 

 Dorsal aorta Carotid artery artery 



Capillary q 

 System " 



Ventral 

 aorta 



Left aortic 

 arch 



'Carofic/ 

 artery 



Subclay-'^ 



lan ^ 

 artery 



to fore 



leg 



Aortic 

 arch 



Pulmonary arte, 

 Righ f aortic arch 



'Aorta 



Carotid 

 artery 



\\Subclav-\ 

 ian , \ 

 artery 

 to "^i 

 ^ I fore leg \ 



Pulmonary 

 artery 



Aorta 



F G H 



Fig. 258. — 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; H, 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 



