4 BONES OF THE HEAD OF FISHES. 



respiration ; of the trunk ; and of the members. The structure 

 of the head is very complicated. At first is seen a central or 

 median portion, composed of a great number of bones united 

 together by sutures, and forming a kind of immoveable keel, 

 with which are connected the bones of the jaw, the cheeks, &c. 

 This median portion, of which the general form is very nearly 

 that of a pyramid with three sides, having its summit directed 

 forwards, has at its back part the cavity of the cranium ; in 

 which is placed the apparatus for hearing, as well as the brain. 

 Its middle side is hollowed out to form the orbital cavities, or ; 

 and in front are seen the apertures belonging to the olfactory 

 apparatus, n ; and a kind of large knob, formed by the vomer, 

 and serving to support the upper jaw (Fig. 247.) We may dis- 

 tinguish the bones corresponding with the occipital, the temporal, 

 the sphenoid, the parietal, the frontal, the ethmoid, and the 

 vomer ; but most of these are composed of several pieces, which 

 never acquire the union that takes place at an early period 

 among the Mammalia and Birds. At the anterior extremity of 



-- op 



FIG. 247. Bones of the head of Pike; c, cranium; or, orbit; n, nasal cavities ; im, 

 intermaxillary bone ; , superior maxillary bone ; t, lateral partition, separating gills 

 from mouth ; p, io, op, bones of operculum, or gill-cover. 



this cranial portion of the head is placed the upper-jaw, which is 

 sometimes fixed there in an immoveable manner, but in general 

 preserves great freedom of motion ; there may be distinguished 

 in it on each side an intermaxillary bone, placed near the medial 

 line, and a maxillary bone, which extends sideways, and which 

 is moveable upon the first. 



521. A chain of small bony pieces extends on each side, from 



