FISHES. 287 



replaces entirely the interorbitary membrane by a continuation of the 

 cavity of the cranium, which extends as far as between the anterior 

 frontalis. In others, the scicena for instance, the interorbitary mem- 

 brane is more or less ossified by productions of the sphenoid, or of the 

 anterior frontals, or even of the ethmoid, which extends into the mem- 

 brane. In some fishes, in fine, the anterior sphenoid is entirely 

 wanting, all this part being membranous. 



This point settled, it only remains to determine the two bones that 

 form the anterior end of the cranium, one above, the other below. 

 The under one, No. (16), is continuous with the sphenoid; the upper 

 one with the frontals and anterior frontals ; moreover, they are joined 

 to each other vertically, and the cavities of the nostrils are situated at 

 their sides, so that they form together the partition. The under one 

 is often furnished with teeth on its inferior surface. I do not hesitate 

 to regard this as the vomer, and the other the ethmoid, that is to say, 

 what is called the vertical lamina of this bone in the mammalia. All 

 their connexions confirm this determination. f 



It sometimes happens, as in the conger, and the common eel, that 

 the ethmoid and vomer form but one bone. 



Thus the cranium of fishes, when its pieces are complete is com- 

 posed of twenty-six bones, vid. six azygos, the basilary (No. 5), the 

 principal sphenoid (No. 6), the anterior sphenoid (No. 15), the 

 vomer (No. 16), the ethmoid (No. 3), and the interparietal or supe- 

 rior occipital (No. 8) • and 20 pairs : the principal frontal (No. 1), 

 the anterior frontals (No. 2), the posterior frontals (No, 4), the 

 parietals (No. 7), the mastoideans (No. 12), the external occipitals 

 (No. 9), the lateral occipitals (No. 10), the petrous bones (No. 13), 

 the great wings (No. 11), and the orbitary wings (No. 14). 



To finish the description of the exterior of the cranium, it should 

 be observed, that it generally presents, behind the occiput, five pro- 

 minent points, which are often prolonged anteriorly or posteriorly 

 into ridges ; the middle one of these corresponds to the spine of the 

 occiput ; it belongs to the interparietal, and often extends forwards 

 over the suture of the frontals, and backwards on that of the lateral 

 occipitals : the spinous processes of the dorsal vertebrae follow in its 

 suite, and are attached to it by a ligament analagous to the cervical 

 ligament of quadrupeds. The second which I call intermediate, 

 there being one on cither side, each runs on the external occipital, and 

 is prolonged forward on the parietal, and sometimes on the frontal of 

 each side. It is to its prominent extremity that the superior branch 

 of the superior bone of the shoulder which I call superscapular, is 

 attached. Lastly, the third ridge, which I call external, belongs to 

 the mastoidean bone, and is prolonged forward on the posterior fron- 

 tal, and on the side of the principal frontal, and backwards on the 

 petrous bone, and lateral occipital ; to its posterior extremity which 



2d. f With my ethmoid, two anterior frontals and vomer, M. Rosenthal forms what 

 he calls, the upper jaw. M. Spix regards my ethmoid as the nasal. M. Geoffroy 

 adopts my determination respecting it, and call it the eifhmosphenal ; but he considers 

 my vomer as the vertical lamina of the ethmoid, and calls it rhinosphenul. M. Bak- 

 ker and M. Meckel agree with me as to both these bones. 



