4 BONES OF THE HEAD OF FISHES. 



Mammalia and Birds ; for, when boiled in water, it does not 

 give out any gelatine. 



540. The skeleton is composed of the head, to which is joined 

 a highly-developed apparatus which is subservient to 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 three-sided pyra- 

 mid, with its summit directed forwards, has at its back part the 

 cavity of the cranium, containing the brain. Its sides are hollowed 

 out to form the orbital cavities, or; and in front are seen the aper- 

 tures belonging to the olfactory apparatus, n; and a kind of large 

 knob, formed by the vomer, and serving to support the upper jaw. 

 (Fig. 347.) We may distinguish 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 



--\ op 



t p io 



FIG. 347. Bones of the head of Pike ; c, cranium ; or, orbit ; n, nasul cavities ; im, intermaxillary 

 bone ; m, superior maxillary bone ; t, lateral partition, separating gills from mouth ; p, to, op, 

 bones of operculum, or gill-cover. 



pieces, which never acquire the union that takes place at an early 

 period among the Mammalia and Birds. At the front of this cranial 

 portion of the head is placed the upper jaw, which is sometimes 

 immoveably fixed, but generally preserves great freedom of motion ; 

 we may distinguish in it on each side an intermaxillary bone, placed 

 near the median line, and a maxillary bone, which extends side- 

 ways, and which is moveable upon the first. 



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



