418 CLASS REPTILIA. 



of organization that its branchial apparatus becomes by 

 degrees, and visibly, a true hyoi'd bone. 



Such a metamorphosis, well ascertained, involves the 

 highest results for osteological theories. Accordingly we 

 find, that it has peculiarly arrested the attention of Messrs. 

 Cuvier, Geoffroy St. Hilaire, and other anatomists of cele- 

 brity. It has been singularly overlooked by M. Steinheim 

 in a work written ex professo, on the development of frogs, 

 in 1820, and by M. Van Hasselt, in a Latin dissertation 

 printed at Groningen in the same year, and on the same 

 subject. 



The Baron tells us in his " Ossemens Fossiles," that 

 when the tadpole is taken at the moment in which its gills 

 are in full activity, and its lungs are no more than a 

 blackish tissue not yet recipient of the air, the ranges of 

 teeth attached to its lips, and the corneous laminae which 

 invest its jaws, serve alone for mastication. Its jaws, 

 scarcely cartilaginous, are very little developed. Its tym- 

 panic bones on the contrary are very much so. To them 

 is suspended the branchial apparatus on each side by a 

 pretty thick and angular branch, which represents that which 

 in the fish, composed of three bones, suspends the whole 

 branchial apparatus to the bone, which our illustrious ana- 

 tomist considers as analogous to the temporal, and which 

 supports the branchiostegous rays. 



Between these two branches is an odd piece, which corre- 

 sponds with the chain of odd osselets placed in the majority 

 of fishes between the first two branchial arches. At its lower 

 point are attached laterally two small rhomboidal pieces, 

 at the external edge of which are suspended the arches which 

 support the gills. These two pieces represent the even osse- 

 lets which terminate the chain just mentioned, and which in 

 many fishes support the two last branchial arches. 



If we afterwards examine tadpoles of more advanced ages, 



