which articulates, by diarthrosis, with a convex tubercle presented to 

 it by the temporal (No. 23). 



Under the posterior and inferior borders of the operculum, there is 

 another osseous piece (No. 32,) which I call the sub-operculum,* and 

 in front of it, under the inferior border of the preoperculum, and behind 

 the articulation of the lower jaw, there is a third (No. 33,) which I 

 call the interoperculum.\ This interoperculum is of particular impor- 

 tance, on account of the attac'inimt it furnishes to the branch of the 

 oshyoides at the place where it is itself attached to the styloid, which 

 suspends it to the temporal, from this it results that the opercular 

 lids can neither open nor close, without the branches of the oshyoids 

 executing a corresponding movement. 



Amongst the common bony fishes, this sort of moving lid which 

 opens and closes the branche, is almost always composed of the 

 three pieces just described. 



We have seen that several ingenious anatomists have imagined 

 them to represent the small bones of the ear in Mammalia ; but besides 

 the arguments, which in another work J we have deduced from the 

 successive simplification of the apparatus of these small bones, and 

 their final reduction to a single bone in the last of the batrachian rep- 

 tiles, the more we examined the opercular pieces the more we shall 

 be convinced, that they do not present the slightest relation with these 

 small bones, either in their connexion with each other, in the con- 

 nexion with other bones, or in the muscles which put them in 

 motion. 



The Lower Jaw. 



The lower jaw is formed of two branches joined together in front, 

 each articulated behind, by a hollow facet with the pully which ter- 

 minates the jugal (No. 26) of its side. In the majority of fishes, 

 when they have attained a certain size each of these branches is 

 composed of two principal bones; the dentary (No. 34) || to the 

 superior borders of which the teeth adhere and the Articular (No. 

 35§ to which the facet for articulation belongs. They unite chiefly by 

 a point of the latter, which penetrates into a re-entering angle of the 

 former. A third smaller bone (No. 36) is frequently detached from 

 the posterior angle under the articular, and may be called the angular*^ 

 and sometimes a fourth is found (No. 37) at the internal surface 

 of the articular ; it corresponds to the opercular in reptiles.** It is 

 only in a few fishes, the lepisosteus for example that the same bones are 

 clearly found, as in the lower jaw of crocodiles, tortoises, and lizards. 

 The fact, however, will not suffice to sustain M. Blainville's opinion, 

 too readily adopted by M. M. Bojanus and Oken, who supposes, 



* The malleal of M. Geoffroy. 



f The inceal of M. Geoffroy, the stapes of M. Spix. 



X Researches on fossil hones. 



|| The subdental of M. Geoffroy. 



§ The submalleal of M. Geoffrey. 



f The subcotyleal of M. Geoffroy. 



** The submoveral of M. Geoffrov. 



