74 ELEMENTARY ANATOMY. [LESS, 



LESSON III. 



THE SKELETON OF THE HEAD. 



I. THE remaining part of the axial endoskeleton is the 

 skeleton of the head, familiarly known as THE SKULL. 



This large rounded bony case for the brain is also the seat 

 of the organs of sense, and forms one coherent mass, except 

 the lower jaw, which in the dry skull readily falls away from 

 the rest. 



Neglecting for the present this lower jaw or, as it is called 

 in zootomy, mandible the rest of the skull is rounded behind 

 and above, and more or less flattened in front, below, and 

 at the sides. Behind and above, it presents a pretty smooth 

 and even surface, crossed by those undulating, interdigitating 

 lines of bony union spoken of in the last Lesson as sutures. 



When sections are made it is seen that the rounded portion 

 forms the roof and hinder boundary of the great cavity 

 in which is lodged the brain, and that irregular bony promi- 

 nences are placed below the front part of that cavity. The 

 skull then may be roughly divided into 



(1) The brain-case, skull proper, or Calvarium. 1 



(2) The skeleton of the face. 



Certain conspicuous openings and prominences occur in 

 different regions. 



The projecting part of the back of the head is termed the 

 occiput, and beneath it is a large hole, looking downwards, 

 termed the occipital foramen. On each side of the front part 

 of this hole is a rounded projection, and these projections, 

 termed occipital condyles, articulate with the cup-shaped 

 hollows on the upper side of the atlas vertebra (see Fig. 89). 



Thus the margins of this foramen coincide with the neural 

 arch of the atlas vertebra, and the interior of the skull forms 

 the expanded summit of the vertebral neural canal \ indeed 



1 From calva, the skull. 



