114 



FISHES. 



" branchiostegal rays " is taken by two broad plates, one 

 on each side, which are known as the "jugular plates" or 

 " gular plates." 



Fig. 4SS. — Skull of Cod (Morrlnta vuJgaris)—Cv.v\er. a, Urohyal ; h, Basili.val ; c, Cerato- 

 hyal ; d, Branchiostegal rays ; p, Praj-operculum ; o, Operinilum proper ; s, Sub-opercuhmi ; 

 i, Inter-operculum ; m, Mandible ; n, Intermaxillary bone. 



The limbs of fishes depart considerably from the typical 

 form exhibited in the higher Vertebrates. One or both pairs 

 of limbs may be wanting, but when present the limbs are 

 always in the form of f.7is — that is, of expansions of the 

 integument strengthened by bony or cartilaginous fin-rays. 

 The anterior limbs are known as the 2'^'^ctoral fins, and the 

 posterior as the ventral fins ; and they are at once distin- 

 guished from the so-called " median " fins by being always 

 disposed in pairs, usually symmetrically. Hence they are 

 often spoken of as the jja-ircc? fins. 



The fore-limbs or pectoral fins possess in a modified form 

 most of the bones which are present in the anterior extrem- 

 ities of the higher Vertehrata. They vary much in size and 

 in other characters. Sometimes they are enormously ex- 

 panded, as in the Flying-fish {Exoccetus) ; and at other times 



