136 ZOOLOGY. 



t ; the occipital, o, behind ; and the sphenoid, s ; and the 

 ethmoid below. These bones are generally broad and flat, 

 of a compact tissue externally 

 and internally, and are immo- 

 vably united by sutures dove- 

 tailed into each other. This 

 adds greatly to the strength 

 of the cranium and of the arch 

 it forms : the interlocking of 

 the sphenoid also with all the 

 other bones of the cranium con- 

 tributes greatly to its general 

 strength. 



Fig. 89.* At the base of the skull 



will be seen a great number of 



apertures for the egress of the cranial nerves, and of the 

 bloodvessels entering or leaving the cranium. In the occipital 

 bone, close to its condyles, is the foramen magnum, by which 

 the medulla spinalis, or " myelon," passes towards the brain ; 

 the vertebral arteries, also intended to supply the brain, enter 

 by this large aperture. The cranium is articulated by means 

 of these two condyles of the occipital bone with the atlas or 

 first cervical vertebra, on which it rests nearly, but not quite, 

 in equipoise, so that during sleep the head naturally falls 

 towards the chest. The powerful muscles moving the head 

 are chiefly placed on the back of the neck. 



At the sides of the cranium may be seen the mastoid pro- 

 cesses (Pig. 91 a), to which are attached the sterno-cleido- 

 mastoid muscles, seen so conspicuously on the front and sides 

 of the neck ; by means of these the head is turned from side 

 to side. Anterior to these may be seen the orifice leading to 

 the middle ear, and to which the external ear is attached 

 ( 222, Pig. 73, .). 



270. The following bones compose the skeleton of the 

 face : the superior maxillary, 2 ; palatine, 2 ; malar, 2 ; lower 

 turbinated, 2 ; lachrymal, 2 ; vomer, 1 ; inferior maxillary, 1. 

 To these some add the intermaxillary, of which the vestiges 

 remain in man, 2 ; the sphenoidal turbinated, 2 ; finally, the 



* f t frontal or coronal; p, parietal; t t temporal; o, occipital; s, the 

 sphenoid; n, the nasal; ms t superior maxillary; j, jugal or cheekbone; mi t 

 inferior maxillary or lower jawbone ; na, anterior opening of the nostrils ; 

 ta, auditory canal or foramen ; az t zygomatic arch ; ab, cd, lines forming the 

 facial angle. 



