182 ELEMENTS OF ORNITHOLOGY. 
cranium which 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-occipitals. 
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 parietals, and in 
front ot these is a pair of frontals, similarly anchylosed together 
and to the parietals. 
The middle of the hindmost part of the floor of the skull is — 
termed the basi-occipital, and immediately in front of this is the 
basisphenoid, 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 medianly conjoined plates of bone called the basi- 
temporals. 
The periotic bones—or “ periotie 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 
ot 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 internus. 
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 part of the 
inter-orbital septum is a small Y-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 called an optic 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 third important 
* Their distinctness and the essential distinctness of different parts 
of the roof and otber portions of the skull is known from their separate 
condition in the skulls of very young birds and of other animals, 
