68 



281. A vertical longitudinal section of the cranium of an Ephippm. 



It shows the three principal divisions of the otocrane ; the upper and posterior excavated 

 in the paroccipital, the upper and anterior in the postfrontal, the lower one in the alisphe- 

 noid and basioccipital : in the middle of these is a portion of the mastoid, which presents two 

 small hut deep depressions, the posterior depression being continued into the exoccipital. 

 This portion of the mastoid, which contributes to form the ' otocrane,' may be regarded as 

 part of the true capsule of the organ of hearing, connate with the proper mastoid, as the 

 entire capsule, or petrosal, becomes in birds and mammals. The alisphenoid gives exit to 

 the chief divisions of the fifth pair of nerves by three or four distinct apertures. It sends a 

 horizontal plate inwards, which meets and unites with a corresponding one of the opposite 

 bone to form the proper floor of the cranial cavity ; and it sends a broad and deep plate down- 

 wards to the basisphenoid forming the antero-lateral part of the basicranial canal. As this 

 canal lodges the origins of the recti muscles of the eye, it may be regarded as a posterior pro- 

 longation of both orbits ; it is partially divided by a descending azygous process from the line 

 of junction of the horizontal plates of the alisphenoids ; the plate is perforated behind this 

 process. 



In this section the compact and finely granular texture of the large fronto-occipital crest 

 and of the thickened frontal is well shown. 



Presented by Prof. Owen, F.B.8. 



282. The dried head of a species of Chcetodon; showing the numerous rows of 

 bristle-shaped teeth in its jaws, to which the name of the genus relates. 



Hunterian. 



283. The skull of a small Ckatodont fish, with a single close-set row of long slender 



denticles having simple obtuse summits, and a stronger recurved laniariform 

 tooth terminating the series posteriorly, in each jaw. 



The orifices of the cavities of the reserve teeth open externally to the bases of those in 

 place. The cranium presents a triangular form ; the occiput is smooth and convex ; the 

 mastoid ridges are thin, but high, and converge and meet upon the parietal region of the 

 cranium. The orbits suddenly expand in front of the contracted cranium ; they intercommu- 

 nicate widely, and are completed below by a slender chain of suborbitals. 



Hunterian. 



284. The premandibular and dentary pieces of a large Chcetodont fish from Sumatra. 



The teeth, though small, are stronger than usual in this family, and differ from 

 those of the Platax in having simple conical pointed crowns. These and the 

 two preceding specimens were transmitted to Hunter, from Sumatra, by his 

 former assistant and artist, Mr. William Bell. Hunterian. 



