1 82 ELEMENTS OE OEJTITHOIOGY. 



cranium whicli adjoin them *. The median part of the skull 

 above the occipital foramen is called the supra-occipital, and the 

 parts on either side of that foramen are termed the ex-occipitah. 



The hinder part of the roof of the cranium, just in front of the 

 supra-occipital, is formed by two bones (not to be distinguished 

 by any line of separation) side by side, called parietah, and in 

 front of these is a pair oifrontals, similarly anchylosed together 

 and to the parietals. 



The middle of the hindmost part of the floor of the skull is 

 termed the basi-ocdpital, and immediately in front of this is the 

 hasisphenoid, in front of which, again, the " rostrum " (before 

 described) projects forwards, and is, therefore, called the 

 sphenoidal rostrum. Behind this, and beneath the basi-occipital, 

 are two medi'anly conjoined plates of bone called the hasi- 

 temporals. 



The periotie bones — or " periotic capsule " — enclose the 

 organ of hearing. An aperture on the external surface of the 

 skull, which is opposite to this capsule, is the opening of the 

 ear, and is called the meatus auditorius externus. The nerve 

 of hearing, " auditory nerve," passes from the brain to the ear 

 through a foramen on the inner wall of the periotic capsule, 

 which foramen is called the meatus auditorius internum. 



The lateral surface of the cranium above the periotic capsule 

 is called the squamosal, and it may develop a forwardly project- 

 ing process. In front of the periotic bone, the side-wall of 

 the cranium is formed by a bone called the alisphenoid. 



In front of the alisphenoids and at the hinder paort of the 

 inter-orbital septum is a small T-shaped bone. The median 

 lower and single part of this is called the presphenoid, and its 

 lateral upward branches the orbito-sphenoids. 



A pair of nerves called " optic " go from the brain to the eye- 

 balls, and pass out at an opening rather low down, in the 

 middle of the front of the cranial box. This opening is divided 

 into two by the hinder end of the inter-orbital septum, and each 

 such division is caHei an opiie foramen. The nerves of smell 

 pass forwards under the roof of the orbits, through a foramen 

 in front of each orbit between the median and lateral ethmoids. 

 This aperture is the olfactory foramen. A thiTd important 



* Their distinctness and the essential distinctness of different parts 

 of the roof and other portions of tlie skull is known from their separate 

 condition in the skulls of very young birds and of other animals. 



