STRUCTURE OF FISHES. .305 



indeed, remain in an imperfectly ossified condition, 

 their elementary pieces being detached from one 

 another, as if the usual process of consolidation 

 had been arrested at an early stage. The texture 

 of the bones of cartilaginous fishes corresponds to 

 this primeval condition ; for it is composed merely 

 of granules of calcareous phosphate, interspersed 

 amidst the cartilaginous substance in detached 

 masses, or presenting the appearance of coarse 

 fibres, thinly scattered through the semitransparent 

 bone. Compared with the quantity of gelatin 

 which enters into their composition, the bones of 

 fishes contain but a small proportion of earthy 

 ingredient ; a circumstance which explains the 

 pellucidity of the mass, and the readiness with 

 wliich the osseous fibres it contains can be distin- 

 guished. Another consequence of the want of 

 density in the bones of fishes is, that their articula- 

 tions are less regular and perfect than the corres- 

 ponding joints of terrestrial animals ; for it is 

 evident that where the parts are soft and flexible, 

 joints are scarcely required. 



In the osseous fishes, the bony structures are 

 more finished ; and they even may arrive at a 

 degree of hardness equal to that of the higher 

 classes. But this developement is not uniform in 

 all the bones ; in the head of the pike, for in- 

 stance, while some of the bones have acquired a 

 great hardness, others remain wholly and perma- 

 nently in a cartilaginous condition. The bones of 

 fishes, however advanced in their ossification, never 

 reach that stage of the process in which cavities 

 are formed ; thus there is no space for marrow. 



