THE TELEOSTEI. 159 



to the epiotic bone, by tbe other to the pterotic, or lower 

 down to the side of the cranium. The base of the fin 

 contains a series of not more than five, more or less ossi- 

 fied, cartilages, which are placed side by side and articii- 

 late with the coraco-scapular ; to these succeed one or more 

 rows of small cartilages, partially hidden by the bases 

 of the exoskeletal fin-rays. The most anterior of these 

 basal cartilages (the mesopterygial basale) is inclosed by 

 the base of the anterior fin-ray, and efi'ects that articula- 

 tion with the shoulder-girdle which is so remarkable in 

 many Siluroid fishes. The posterior cartilage, or bone, is 

 the metapterygial basale, and the intermediate thi-ee are 

 radialia (p. 40). 



Most Teleostei possess teeth, and, in the majority of these 

 fishes, teeth are very widely distributed over the surface of 

 the walls of the oral and phaiyngeal cavities. The teeth 

 vary very miich in structure; ordinarily, they consist of 

 dentine, cajDped with structui-eless enamel. The parietes 

 of the tooth are not unfreqiiently longitudinally folded 

 towards the base, but this folding never goes so far as in 

 the Ganoids. The different kinds and modes of arrange- 

 ment of the teeth may be classified as follows : — 



1. Isolated, more or less pointed teeth, developed from 

 papillae of the mucous membrane, which do not become in- 

 closed in sacs — frequently ankylosed to the subjacent bone, 

 but not imbedded in alveoli, nor replaced vertically. 



The great majoi'ity of oxxiinary osseous fishes have teeth 

 of this kind. 



2. Isolated teeth, which become imbedded in sockets, and 

 are replaced vertically. 



Such teeth are seen in the premaxillas of Sargus, where 

 they curiously simulate the form of human incisors ; and, 

 imbedded in the coalesced hypopharyngeal bones, in Labrns. 



3. Isolated teeth, imbedded in the substance of the bone 

 which supports them. The teeth and the supporting bone 

 wear away in front, and are replaced by new teeth developed 



I behind the others. This structure is seen in the coalesced 

 hyijojiharyngeal bones of the Parrotfish (Scarus). 



