646 DR JAMES STARK ON THE EXISTENCE OF AN OSSEOUS STRUCTURE 



peculiarities of no inconsiderable interest. In the Sharks, Skates, and other 

 genera belonging to this important division of the great class we are now consi- 

 dering, the interior of the bones remains permanently cartilaginous; but the 

 skeleton is in some regions encrusted, as it were, with osseous granules. No 

 centres of ossification, from which radiating fibres of bony matter progressively 

 extend themselves, as is the case in the osseous fishes, are ever developed."* 



Such, then, is the amount of information relative to the vertebral column of 

 the cartilaginous fishes, contained in works known to me. The beautiful descrip- 

 tions of Sir EVERAED HOME, of the intervertebral apparatus of the Sharks and 

 rays, have been omitted to be noticed, as it is of the bones alone I purpose to 

 make any mention in this communication. 



In the course of investigations into the structure of the skeletons of the ver- 

 tebrated animals, I procured the vertebral column, and some of the other solid 

 parts of the Common Skate (Raia batis), Thornback Ray (R. clavata), Starry 

 Ray (R. radiata), and Sharp-nosed Ray (R. oxyrhynchus), for the purpose of sub- 

 mitting them to a chemical examination. The bones or cartilages were carefully 

 cleaned of all fleshy and other matters, dried till they ceased to lose weight, and 

 were then burned. As I had been prepared to expect, the calcareous granular 

 particles which were seen very distinctly on the surface of the cartilages, were 

 procured in the state of a loose granular powder ; but I was not a little surprised 

 to find that each vertebra yielded, at the same time, a solid osseous nucleus, very 

 analogous in form, and somewhat resembling in structure, the bony vertebrae of 

 the osseous fishes. 



A careful examination of the vertebral column of these animals satisfied me, 

 that this internal nucleus consisted not of agglutinated calcareous particles, re- 

 sembling those scattered over the surface of the cartilaginous skeleton, but of 

 true bone, having the same general structure as the vertebrae of osseous fishes, 

 being, like them, composed of concentric rings, or laminae of osseous matter. In 

 these fishes, however, this osseous nucleus was highly condensed, so as to cause 

 it to resemble ivory itself; and in consequence of this condensation, the fibrous 

 structure could not be distinctly seen in it. 



It further appeared, that the essential part of each vertebra was composed 

 of this truly osseous substance, and that the whole of the external cartilaginous 

 covering, with its interspersed calcareous grains, could be removed without inter- 

 fering with the integrity of the vertebral column, in so far as the union of the one 

 vertebra to the other was concerned. In fact, it was by means of this osseous 

 portion, that solidity and strength were given to the whole vertebral column ; 

 and it was to this osseous portion, and to it alone, that the intervertebral liga- 

 mentary apparatus, so well described by Sir EVERARD HOME, was attached. 



* JONES, p. 505. 



