CHONDROPTERYGII. 197 



Thus we have seen the bony skeleton, the scaf- 

 folding on which the whole structure of the animal 

 is built, gradually changing from the dense and 

 solid character which it assumes in the Birds and 

 Mammals, to the tough and flexible bones of the 

 proper Fishes, thence to the gristle of the Sharks 

 and Rays, and finally to a form and texture scarcely 

 distinguishable from the vestige which still lingers 

 in the highest of the INVERTEBRATA. 



