CLASS OF FISHES. 



373 



composed of a head, trunk, and limbs, with a hyoid apparatus 

 largely developed, and assisting in respiration. 



478. The structure of the head is very complex, and 

 composed of many bones ; its median portion (Fig. 383) 

 presents behind a cranial 

 cavity (c), lodging the 

 organ of hearing as well 

 as the brain. About the 

 middle are the orbital 

 cavities (or), and ante- 

 riorly, the cavities belong- 

 ing to the olfactory appa- 

 ratus (ri) and a kind of 

 large prominence formed 

 by the vomer, and support- 

 ing the upper jaw (Fig. 

 384 v). The analogues of 

 the occipital, temporal, 

 sphenoidal, parietal , frontal , 

 ethmoidal, and vomer may 

 readily be recognised, but 

 most of these parts are 

 composed of several pieces, 

 the original germs of these 

 bones, which never unite 

 in fishes. 



Anteriorly, is found the 

 upper jaw, which is some- 

 times fixed, but more 

 usually very moveable ; on 

 each side are an intermaxil- 

 lary bone (im) and a maxil- 

 lary bone (m), which is 

 moveable on the first. 



A chain of small bones 

 extends on each side from 

 the anterior angle of the 

 orbit to the posterior, and 

 thus completes the orbital 

 circle. Deeper may be seen on each side a kind of vertical 

 partition suspended to the cranium, and separating the orbits 

 and cheeks from the mouth. It is formed by the analogues 

 of the palatine, pterygoids, tympanics, &c., and articulates 



Fig. 382. Skeleton of the Perch. 



