CARTILAGINOUS FISHES. 291 



ORDER IV. CARTILAGINEI. 



(Cartilaginous Fishes.) 



The largest and most formidable of all fishes 

 are found in this Order. " The peculiar struc- 

 ture of their skeleton, which gives rise to their 

 name, admits of these animals continuing to grow 

 as long as they live ; the consequence of which 

 is, that as they inhabit the wide ocean, and have 

 few enemies, they are sometimes met with of such 

 an enormous size that their weight and dimen- 

 sions are almost incredible."* 



The great essential character of the Order is 

 the nature of their skeleton. Their bones have 

 but a very small quantity of earthy matter in 

 their composition ; and what is present is deposit- 

 ed in grains, and not in distinct fibres. The 

 skull is not divided into separate bones, but is 

 formed in a single piece ; yet ridges, furrows, 

 and holes on its surfaces, enable the anatomist 

 to discover the portions, which in other fishes 

 are distinct, though here soldered, as it were, 

 together. Even bones, that in other fishes con- 

 stitute moveable joints, are not always distinct 

 in this Order ; the vei'tehrce or joints of the spine, 

 for example, are, in some of the Rays, united into 

 a single mass ; and in other genera, some of the 

 bones of the face are quite wanting. The bones 

 of the jaws, known to anatomists under the names 



* Swainson, Nat. Hist, of Fishes, i. 118. 



