THE FISH. 5 



jugal bone, a tympanic and squamous bone, consti- 

 tutes, as among birds and snakes, a sort of interior 

 jaw, and supplies behind an articulation to the lower 

 jaw, which has in general two bones on each side, 

 but these pieces are less numerous in the chondrop- 

 terygii. 



Teeth are found on the intermaxillaries, the max- 

 illaries, the lower jaw, the vomer, the palatines, the 

 tongue, the arches of the gills, and even on certain 

 bones situated behind these arches dependent like 

 them on the os hyoides, and named ossa pharyngis. 



The varieties of these combinations, as well as 

 the forms of the teeth placed at each point, are 

 countless. 



Independently of the apparatus of the branchial 

 arches, the os hyoides carries on each side certain 

 rays which support the branchial membrane ; a kind 

 of lid composed of three bony pieces, the operculum, 

 the sub-operculum, and the inter-operculum, is joined 

 to that membrane to close the great opening of the 

 gills ; it is articulated to the os tympani, and moves 

 upon a piece called the pre-operculum. Many of the 

 chondropterygians have not this apparatus. 



The stomach and intestines vary as much in volume, 

 figure, weight, and circumvolutions, as in the other 

 classes. Except in the chondropterygians the pan- 

 creas is represented either by cceca of a peculiar 

 tissue, situated round the pylorus, or by this same 

 tissue itself at the beginning of the intestines. 



The kidneys are fixed along the sides of the spine, 



