FISHES. 285 



frontal ones, but they touch one another only very rarely ;* almost 

 always they are separated by means of an azygos bone from which 

 the occipital spine proceeds vertically, it being very large in a great 

 number of fishes, and is frequently prolonged anteriorly into a true 

 sagittal crest. In such a case we are naturally tempted to give to this 

 azygos bone, the name of interparietal;! but sometimes, as in the 

 carp for example, the parietals touch one another for a considerable 

 portion of their length, and then the bone just mentioned, is behind 

 the parietals, and thus must be considered as a superior occipital : its 

 function would therefore resemble very much that which belongs to 

 it in the tortoise. In some fishes, but especially in the family of the 

 silures, the parietals are wholly absent, and are replaced by this azygos 

 bone in a very large state of development. 



On the sides of the latter, as in the tortoise, there are two pairs of 

 bones which form the lateral portions of the occiput, these cor- 

 respond exactly to those, which I have designated in the tortoise, as 

 the external occipital (No. 9,) and lateral occipital (No. 10.) 



It would perhaps be better to call the single bone of which I have 

 spoken, the interparietal, in which case, the two external occipitals 

 might be regarded, as a superior occipital divided into two ;t they 

 both form the summit of the first lateral ridge of the cranium, that 

 which I call intermediate, to which one of the apophyses of the supra 

 scapular is attached. On the inside of the cranium, the lateral occi- 

 pital (No. 10,) often furnishes a lamina, which unites with its fel- 

 low, to form a roof for the sacs in which the stones of the ear are en- 

 closed. It sometimes presents a singular conformation, in the carp, 

 being pierced with a large hole. 



The basilar or inferior occipital (No. 5) occupies its usual place, 

 and the articular facet forming a hollow cone, by which the head is 

 attached to the body of the first vertebra, entirely belongs to it; but 

 the other two small facets, which, in a great number of species con- 

 verge to the articulation of the head with the articular facets of this 

 vertebra, belong to the lateral occipitals (No. 10.) 



Before the lateral and inferior occipital, from each side of the 

 noid arises the great or temporal tving, which always unites by suture 

 to the posterior frontal (No. 4) J and furnishes conjointly with it, an 

 articular facet to the temporal bone. The two last branches of the 

 fifth pair pass through a hole or fissure of this piece. In the inside of 

 the cranium, this great wing often gives anteriorly a roof to the pitui- 

 tary gland in the same manner as the lateral occipitals cover the 

 stones of the ear. 



* It would appear now that at last all the world, with even M. Geoffroy at the 

 fag-end, is agreed respecting the parietals. 



■f M. Geoffroy has decided by giving also to this the name of interparietal, and I 

 am not aware of any person who does not coincide in its propriety. 



X M. Geoffroy has also adopted this determination, he calls these two pair of 

 bones, the superoccipital, and exoccipital. M. Bojanus calls the external occipital, 

 interparietal. 



| M. Geoffroy who has at length adopted the same determination, calls it ptereal. 

 All uaturalists are now agreed respecting this bone, with the exception of M. Rosen- 

 thal and M. Meckel, who look upon it as the petrous bone. 



