33 ORDER SELACIIII; GENERAL CHARACTERS. 



cartilaginous fishes, below the forms with a true bony skeleton, in 

 which he has been followed by most subsequent writers, includ- 

 ing even Professor Miiller, there seems to be sufficient reason for 

 removing them from this degraded position, and placing them at 

 the head of the whole order. In their general organisation they 

 certainly stand higher than any other Fishes ; the development of 

 the brain, and especially that of the cerebral hemispheres, is far 

 superior to that of the other members of the class ; and this in- 

 dicates a greater degree of intelligence. In some respects, in- 

 deed, they approach the Reptiles ; and this appears to have been 

 to a certain extent perceived by Linnaeus, as he arranges the 

 whole of the Cartilaginous Fish, and a good many of the more 

 singular Osseous forms, in his class of Amphibia. 



576. The skeleton is always of a cartilaginous nature, ex- 

 cept in a few species, in which the vertebral column is replaced 

 by a gelatinous cord, called the chorda dorsalis, analogous to 

 that which is met with in the embryonic states of other Fishes. 

 The cartilaginous vertebrae of the majority of the order exhibit 

 the ordinary conical cavities on their anterior and posterior sur- 

 faces ( 543), and their processes are inserted into small sockets, 

 which are the small round holes seen in the dried back-bones of 

 Sharks, sometimes manufactured into walking-sticks. The fins 

 are usually of large size, and supported by strong rays ; amongst 

 which some occasionally acquire the texture of dentine, or the 

 fundamental substance of the teeth. The pectoral and ventral 

 fins are always present, and the former are frequently of enorm- 

 ous size, whilst the latter are furnished with peculiar filamentous 

 appendages in the males of many species. The tail is always of 

 considerable length and strength, and usually furnished with 

 large fins, which are arranged in such a manner that the fleshy 

 part of the tail reaches the extremity of the organ, generally 

 forming the principal part of its upper branch. The Fishes in 

 which this unsymmetrical structure of the tail occurs are called 

 heterocercal ; they belong exclusively to this and the following 

 order. The skin is sometimes entirely naked, sometimes beset 

 with asperities of dentine ; these are sometimes of small size, and 

 cover nearly the whole skin ; whilst in other cases they form large 



