334 



ZOOLOGY. 



The lungs of the 'adult batrachia have but a few incomplete 

 cells; they receive the blood from two small branches <>f tin- 

 aorta, these performing the office of a pulmonary artery. 

 Thus the pulmonary respiration is feeble, but the cutaneous 



Fig. 303. Skeleton of the Frog. 



makes up for it by its activity. When the temperature is low it 

 is sufficient to maintain life. Frogs breathe by the action of 

 deglutition, so that to suffocate the frog it is only necessary 

 to hold its mouth open for a time. This mode of breathing 



Fig. 3<U Rainette. 



is necessitated by the' incomplete state of the skeleton of 

 the adult frog ; the ribs are wanting, and thus the thorax can 

 no longer be dilated, as in mammals, birds, and ordinary rep- 



and that it is with them rather than with the branchial vessels that the 

 arteries coming from the heart seem to be continued. The pulmonary 

 arteries are also much developed. Fig. 302. The same parts in the perfect 

 animal, indicated by the same letters ; the vessels which in the tadpole went 

 t.. tin- \\\ branchiae of the second pair, are continued now with the aorta by 

 the intermedium of the anastomotic branches (2), and thus constitute the 

 two aortic arches. 





