138 THE AXATOMY OF VERTEBRATED ANIMALS. 



Siluroids, by sutural union. By its inner surface it gives 

 attachment to the coraco-scapular — and sometimes above 

 them, to a styliform bone which extends back among the 

 lateral muscles — the 2^ost-clavicula {2:>.cl.). 



Attached to the dorsal end of the clavicle, there is usually 

 a second much smaller bone, the siqyra-clavicula {/S.cl.), and 

 this is very generally connected with the skull by a superficial 

 membrane bone, the 2^ost-temporal, which, in front, becomes 

 forked, and attaches itself by one prong to the epiotic bone, 

 by the 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 ossified, cartilages, which are placed 

 side by side and articulate 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 mesopterj-gial basale) is enclosed 

 by the base of the anterior fin-ray, and effects that articulation 

 with the shoulder-girdle which is so remarkable in many Silu- 

 roid fishes. The posterior cartilage, or bone, is the metaptery- 

 gial basale, and the intermediate three are radialia (p. 39), 



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 pharyngeal cavities. The teeth vary 

 very much in structure ; ordinarily, they consist of dentine, 

 capped with structureless enamel. The parietes of the tooth 

 are not unfrequently longitudinally folded toward the base, 

 but this folding never goes so far as in the Ganoids. The dif- 

 ferent kinds and modes of arrangement 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 en- 

 closed in sacs — frequently anchylosed to the subjacent bone, 

 but not imbedded in alveoli, nor replaced verticallj^ The great 

 majority of ordinary 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 i:)rcmaxill9e of Sargiis, where 

 they curiously simulate the form of human incisors ; and, im- 

 bedded in the coalesced hypopharyngeal bones, in Lahms. 



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

 which supports them. The teeth and the supporting bone 

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

 behind the others. This structure is seen in the coalesced 

 hj^popharyngeal bones of the Parrotfish {Scarui). 



