294 FISHES. 



just stated, the jugal which I consider it to be, notwithstanding all 

 the singularity, of its change of place and functions.* The thin flat 

 piece (No. 27) situated between the temjioral and jugal, will then no 

 longer represent the body of the tympanal, or caisse deprived of its 

 articular facets, because it is no longer required to concur in deter- 

 mined motions which are provided for in its stead, by the two 

 bones which are attached to it above aud below ; it is also reduced to 

 a flat disk, because it is no longer required to contain either the 

 cavity of the caisse, or the small bones of the ear.f 



We have remaining the seventh bone (No. 31") that which is 

 partly concealed behind the internal surface of the jugal ; I can find 

 nothing analogous to it in reptiles ; for I do not consider as such, the 

 bone which forms a slender column in the lizards ; this bone, there- 

 fore, I shall call the si/mplecficl 



These seven bones are joined together, and to the preoperculum by 

 synchondrosis, and have little or no motion on each other ; but to- 

 gether they form a large lamina, Avhich moves with facility on the 

 two hinges furnished to it by the anterior artictilation of the palatine 

 (No .22,) with the maxillary (No. 18,) with the vomer (No. 3,) and the 

 superior articulation of the temporal (No. 23,) with the posterior 

 frontal (No. 4,) the mastoidean (No. 12,) and with the great wing 

 (No. 11). This movement separates the lower borders of the lamina 

 from each other, and widens the mouth, when the fish takes in the 

 water necessary for its respiration ; the contrary movement forces the 

 water out. 



Opercular Bones.\\ 



The preoperculum (No. 30)§ is a bone commonly of a square form, 

 which surrounds the posterior border, and the angle of the great 

 palato-temporal lamina described above, and belongs to this lamina 

 rather than to the opercular system itself. Its form, and the indenta- 

 tions or spines, with which its border or angle are often armed vary 

 much ; and as these variations are visible externally, they have 

 aff"orded proper charactex's for the distinction of fishes. 



The principle piece of the operculum ^ to which I leave this name 

 exclusively (No. 28,) is situated behind the ascending border of this 

 preoperculum, and moves on it as the fold of a door on its hinge; but 

 at its upper anterior angle, the operculiun presents a small dimple 



* This is^ the hypocofi/leul of "M. Geoffvoy, the os 'discoidetim of M. Caius, the 

 internal pterygoid of M. 13ojamis, the sympJecticum quartum of M. Bakker. 



-f- This is the epicotijleal of M. Geoffroy, the symplecticum tcrtium of M. Bakker, 

 the external pterygoid apophysis of M. Bojanus 



X This is the uro-serial of M. Geoffroy, the symplecticum secundum of M. Bakker, 

 the styloid of M. Meckel. The other anatomists seem to have neglected this piece, 

 which is not very apparent. 



II For all that concerns the skeleton of the respiratory apparatus of fishes. M. 

 Geoffroy's, where Anatomical Philosophy may be usefully consulted, in which the 

 parts of this apparatus are described with great care, and represented very faithfiilly, 

 although the author's theory is, in my opinion, very far from satisfactory. 



§ The tympanal of M. GeoflFroy, the malleus of M. Spix. 



^ The s^apeai of M. Geoffroy, the incus of M. Spix, the ojjerculum of all other 

 anatomists. 



