FISHES. 411 



their articulations are less regular and perfect 

 than the corresponding joints of terrestrial ani- 

 mals; for it is evident that where the parts are 

 soft and flexible, joints are not required. 



In the osseous fishes, the bony structures are 

 more finished ; and they even 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 instance, 

 while some of the bones have acquired a great 

 hardness, others remain wholly and permanently 

 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, 

 nor even for the cellular or cancellated structure 

 which we have noticed in the more perfect bones.* 



184 



p 



The general disposition of the bones which com- 

 pose the entire skeleton will be understood from 

 Fig. 184, which represents that of the Cyprinm 



* Cuvier, sur les Poissons. Tom. i. p. 218. 



