FISHES. 283 



and opens or shuts according as the*motion of the water for respira- 

 tion may require. 



Of the Cranium. 



It is between these four apparatuses, the maxillary, suborhitar, pte- 

 rygo-tympanic and opercular, that we find the cranium or cerebral box, 

 which, as usual, contains the nose and eye in the external fossce, the 

 of the ear in the internal lateral cavity, and in its general cavity, the 

 labyrinth brain; this cranium, as in other vertebrated animals, is a 

 sort of a cage or envelope, composed of pieces which are united, 

 so as to be immovable, by sutures. 



The cranium in the Acanthopterygians may be regarded as the most 

 correct type, in other words, it is that cranium in which the bony 

 constituents are most approximated to their complete state, and 

 themost advanced in their developement respectively : they un- 

 dergo a variety of modifications in the other orders, but in such a 

 way as that when once the student establishes in his mind a complete 

 idea of this primary form, he can always, with the greatest facility, 

 determine the rest by induction. Between the skulls of the reptiles 

 and the birds, a striking analog)'' is observed* in both, for it is 

 by no means difficult to find the whole of the parts, and this will be 

 manifest to those who will take the trouble of examining with us now 

 one of the crania ; that of the common perch for example. In the 

 other acanthopterygians we have the same bones, with the difference 

 only of proportions between these individual bones and the aggregate 

 which they compose. This is likewise the reason why we cannot limit 

 ourselves to a mere generic description of them according to their number, 

 connexions; and functions, without at all entering into the details of 

 their figures, which would be only convenient in this single instance, 

 and, perhaps, would only perplex the other part of the explanation f , 

 pi. I. A. the superior face fig. 1. the principal frontal, forming the 

 arch fig. 1, of the orbit and the anterior portion of that of the cranium. 

 Both before and behind it there are bones which form the anterior and 

 posterior pillars of the orbit, and which correspond to the anterior and 

 posterior frontals of the reptiles. 



* It is recommended to the reader to peruse the portion of the chapters in my 

 work, on the Fossil Bones, where I have described the cranium of the reptiles. 



-f- In order to facilitate the study of the osteology of fishes, that of the perchis is 

 given in all its particulars in plates I, II, III. Plate I, presents the entire 

 skeleton ; it gives a lateral view of the entire head, and also the apparatus of the 

 face in their natural situation. Figures I, II, III, IV, of plates II, give the 

 cranium and the pieces composing it, as seen in fig. I. in a lateral aspect, fig. II. 

 the upper part, fig. III. the upper part, fig. IV. the hind part. Fig. V. is the 

 cranium seen from below with one side of the face ; the gills are removed. Fig. 

 VI. presents, on the contrary, the cranium from which the apparatus of face have 

 been taken away to show the attachment of the gills and the shoulder. Fig. VII. 

 is a vertical and longitudinal section of the cranium, the left half being removed to 

 show the inside part of the right. Fig. VIII. is a vertical and transverse section, 

 showing its anterior side from within. Fig IX. is the part opposite the same 

 section, and shows within the posterior side of the cranium. Lastly, the Fig. X. is 

 a horizontal section, which shows the root of the skull. In all these figures the 

 same bone has the same number. 



