98 THE STKUCTUEE OF THE HOUSE 



two main portions : (1) the cranium, or skull proper, 

 consisting of a great number of bones, originally quite 

 distinct, but which are eventually firmly united so as to 

 form a solid mass; 1 and (2) the mandible, or lower jaw, 

 fastened to the former by a freely movable hinge-joint. 



The cranium is movably joined to the front end of 

 the vertebral column by means of a pair of oval emi- 

 nences called c condyles,' which fit into corresponding 

 cavities in the atlas, or first vertebra of the neck. 

 Between these condyles is a large opening {foramen 

 magnum), through which passes out of the cranium the 

 spinal cord, or backward prolongation of the central 

 nervous system, which is expanded in the head to form 

 the brain. 



The cranium may be roughly divided into two 

 portions — a hinder part, or brain-case, consisting of 

 a solid bony capsule for enclosing and protecting the 

 brain ; and a facial part, for the support of the organs of 

 sight, taste, and smell, and of those concerned in seizing 

 and masticating the food. 



The skull of a man (fig. 15) and the skull of a 

 horse (fig. 16) are composed of exactly the same 

 number of bones, having the same general arrange- 

 ment and relation to each other. Not only the indi- 



1 The outlines of the individual bones are perfectly well marked 

 in young subjects, being indicated by fine dividing-lines, called 

 sutures. In old age these often become more or less obliterated by 

 the union of the contiguous bones. 



