702 KEPTILIA. 



mass (2, 3, 4) composed of the three united branchial arches becomes 



Fig. 346. 



c r> 



Metamorphoses of the os hyoides in the Tadpole. (After Dr. St.-An S e.) 



insensibly obliterated, and in a very few days is entirely absorbed. 



While this absorption is going on, the 

 branchial arch (1) assumes greater 

 consistency, its inferior extremity be- 

 comes directed outwards, and it loses 

 the little cartilaginous teeth previously 

 appended to it; the os hyoides thus 

 assumes the simple form represented 

 in fig. 346, c. Lastly, the cartilage 6 

 disappears, and the complex branchial 

 apparatus of the tadpole becomes con- 

 verted into the permanent and com- 

 paratively simple os hyoides of the 

 Salamander, depicted in fig. 346, D. 



(1971.) The branchial arches 2, 3, 4, 

 Dr.St.-Ange remarks, are absorbed in 

 proportion as the circulation becomes 

 modified, their atrophy depending upon 

 the change which takes place in the 

 course of the blood, owing to the di- 

 latation of the anastomotic vessels 

 (fig. 345, e e e) and the enlargement 

 of the pulmonary arteries (&). It is, 

 therefore, owing to a kind of revulsion 

 produced by the afflux of the blood 

 towards the pulmonary organ instead 

 of towards the branchiae, that the 



Fig. 347. 



Course of the circulation in Lepido- 

 siren. (After Owen.) 



