42 OSTEOLOGY. 



outwards, and is bounded internally by a rough line, the parietal 

 crest, and externally by the superior edge of the zygomatic 

 process. It lodges the temporal muscle and the lever process 

 of the lower jaw, and contains many foramina, which lead to a 

 cavity between the bones called the parieto-temporal conduit. 



The Posterior part or base of the skull presents superiorly the 

 roughened occipital crest continued downwards by the sharp 

 mastoid ridges, which again are continuous with ridges on the 

 squamosal bones, and so with the upper edges of the zygomatic 

 arches. Below the crest is a broad, slightly-roughened surface, 

 and below that, in the median line, is the neural canal of the 

 occipital bone, called the foramen magnum, bounded laterally 

 by the condyles, which again are flanked by the styloid processes, 

 and separated from them by the stylo-condyloid notches. 



The Anterior part or apex, formed by the premaxilla and body 

 of the inferior maxilla, contains the incisor teeth, and is more or 

 less rounded in profile, according to the age of the animal. In 

 front, it is surmounted by the external opening of the nasal 

 cavities ; this opening, included between the premaxilla and the 

 nasal spine, is divided, in the fresh subject, into two orifices, the 

 anterior nares. 



CAVITIES IN THE SKULL. 



The skull contains internally the cranial cavity, the nasal 

 fossai or chambers, and the sinuses, which are appendages to the 

 latter. 



CRANIUM. 



The Cranium is an extremely irregular ovoid cavity, the walls 

 of which are formed by the frontal, parietal, occipital, temporal, 

 sphenoid, and ethmoid bones. For the purpose of description, 

 it may be regarded as being divisible into a roof, a floor or 

 inferior surface, two lateral surfaces, and two ends. 



The Roof presents, towards its posterior third, in the median 

 line, the parietal protuberance, or o&sific tentorium, which, with 

 the two lateral ridges springing from it, and which may be 

 regarded as a part of it, assists in dividing the cranial cavity into 

 two compartments a posterior one, for the cerebellum, and an 

 anterior, considerably larger, for the cerebrum. Along the 

 median line, from this eminence to the front of the roof runs 

 a groove, the roughened elevated borders of which form a rudi- 



