530 



METAMORPHOSES OF BATRACHIA. 



br.'i 



Fishes, the blood follows the same course ; but when the lungs 



are developed, the arrange- 

 ment of the vascular appa- 

 ratus changes ; there is esta- 

 blished a direct communi- 

 cation between the arteries 

 which carry the blood to 

 the gills, and those which 

 return it from these organs ; 

 so that the nutritious fluid 

 is no longer compelled to 

 traverse this apparatus of 

 aquatic respiration, in order 

 to arrive at the dorsal artery, 

 and thence into the different 

 parts of the body (Fig. 

 339). The artery (a) which 

 arises from the ventricle, 

 and which might be at first 

 compared to a branchial 

 artery, then becomes the 

 origin of the dorsal trunk, and forms with it a true aorta ; of 

 which certain branches, that are sent to the lungs, are developed 

 at the same time, and establish the pulmonary circulation. 

 Finally, the branchial vessels are obliterated, and then the cir- 

 culation becomes almost the same as in true Reptiles (Fig. 340). 

 The venous blood, returning from every part of the body, is 

 poured into the ventricle by one of the auricles, and is there 

 mixed with the arterial blood coming from the lungs, and forced 

 into the same ventricle by the other auricle. This mixture then 

 passes into the aorta ; a small part of it being distributed to the 

 lungs, and a larger part to the different organs of the animal. 



523. Certain Batrachians undergo less complete metamor- 

 phoses. Thus Salamande/s, like Frogs, acquire members in the 

 progress of time and lose their gills ; but they also preserve their 

 long tail (Fig. 344) : and, as we have already stated, there are 

 also some of these creatures which, as regards their mode of re- 

 spiration, always remain in the tadpole state ; for their gills are 



\ 



FIG. 340. The same, in the perfect animal ; 

 the gills have now disappeared, and the course 

 of the blood is entirely through the communi- 

 cating branches ; that of the first pair conveys 

 it direct to the trunks, t, t, supplying the head ; 

 and those of the second and third to the aorta, 

 ay. The respiratory circulation is now entirely 

 carried on by the pulmonary arteries, ap. 



