18 



Vertebrata. 



pectoral fins, are placed directly behind the head, to 

 which indeed the shoulder girdle is in most fishes 

 united by small dermal ossifications. The hind limbs 

 are called the ventral fins, and are rarely as well de- 



Skull of Cod. 



3, supra-occipital bone ; 4, opisthotic ; 8, post-temporal : n, frontal ; 9, 

 parasphenoid bone ; g, g; sub-orbital bones ; 22, premaxilla ; 21, maxilla ; 

 24, pterygoid ; 28, hyomandibular ; 29, articular piece of lower jaw ; 23, 

 dentary bone ; 39, 40, 41, 43, hyoid arch ; 44, branchio-stegal rays ; 34, 

 35> 36, 37, opercular bones. 



veloped as the fore limbs, and the pelvic girdle is 

 seldom attached to the vertebral column. The fins 

 are of use in directing, the motion of fishes, while the 

 tail is the principal organ of propulsion. 



