FISH IN GENERAL. 55 



the ear in an internal and lateral cavity, and the encephalon 

 in the great cavity in the middle : it is composed of pieces 

 firmly united by sutures. 



In the cranium of the perch, serving as a type of all the 

 acanthopterygians, we find on the superior aspect the prin- 

 cipal frontal (No. 1); the anterior frontals (No. 2) form the 

 anterior surface pillar where the olfactory nerves pass, the 

 ethmoidal (No. 3) constituting a vertical partition ; the pos- 

 terior frontal (No. 4) is the after pillar of the orbit, and aids 

 in the articulation of the temporal (No. 23) : the axis of the 

 inferior face is occupied by the basilar]/ (No. 5), and the 

 sphenoid (No. 6), the parietals (No. 7), are easily known 

 behind the frontals ; they are usually separated by an odd 

 bone (No. 8), which we may name interparietal. On the 

 sides of it are two pairs of bones, the external occipital (No. 9), 

 and occipital lateral (No. 10); this last pair often forms on 

 the inside a kind of floor above the auditory sacks containing 

 the auricular stones. The inferior occipital, or lasilary 

 (No. 5), occupies its proper place, and its articulating surface, 

 shaped like a hollow cone, attaches the head to the first 

 vertebra, but two other small surfaces, which in many fish 

 assist in this attachment, belong to the lateral occipital 

 (No. 10). On each side of the sphenoid, and before the lateral 

 occipital and inferior occipital, rises the great ala or temporal 

 ala (No. 11), always united by suture to the posterior frontal 

 (No. 4); at the lateral posterior, and superior angle of the 

 cranium, there are always on each side between several of the 

 above-named bones, two others, the first is the mastoidean 

 (No. 12) ; the second, large in gadi, but small in acanthop- 

 terygians, is the rock or rupes (No. 13). In front of the great 

 ala, and fixed to it is the orbitary ala (No. 14) ; beneath and 

 before them is a single bone usually planted into the sphenoid : 

 it is the anterior sphenoid (No. 15). Two bones form the 

 anterior extremity of the cranium : the one above is the 



