STRUCTURE OF FISHES. 423 



from the cranium ; a fact which may be cited 

 in further corroboration of the analogy which 

 the cranial bones have to vertebrae. 



In the ray and the shark tribes, both the ante- 

 rior and posterior extremities are supported by 

 arches of bones, forming a sort of belt. This 



structure is an ap- 

 proach to that which 

 obtains in many rep- 

 ^' tiles, and indicates a 

 further step in the regular progress of develope- 

 ment. This belt in the ray is shown in Fig. 193. 

 In examining that part of the skeleton of fishes 

 which corresponds to the posterior extremity, we 

 observe the total absence of both femur and 

 tibia ; but the bones of the toes are attached to 

 a set of small bones, which appear to act the 

 part of a pelvis, but which, in consequence of 

 their not being connected with the spine, have 

 no determinate situation, and are found at various 

 distances from the head in different fishes. 

 They appear emancipated from the restraints to 

 which they would have been subjected had they 

 been fixed to a sacrum, or to any particular 

 part of the spine : and we find them, accord- 

 ingly, often placed considerably forwards ; and 

 in some instances, as in the Suhbrachieni, even 

 anteriorly to the pectoral fins, which are the 

 true arms of the animal. But in one whole 

 order of fishes, the Apodes, there is not even a 



