THE SKELETON 



17 



thin, dense plates, separated by a considerable 



thickness of bone of a spongy texture. The 



spaces of the spongy bone contain air derived 



from the auditive tubes 



of Eustachius. A very 



noticeable feature of the 



skull is the presence of 



a large, hemispherical 



tympanic cavity on each 



side of the hinder part 



of the cranium. The 



cavity forms the drum 



of the ear wlien the soft 



structures of the head 



are in position. 



1. Cranial Bones. — 

 The occipital bone forms .,*?"" ^f™"" '"-'S""™; o-^- ocd- 



*^ pital condyle; O., occipital; B.t., basi- 



the most posterior part temporal; XH., foramen for hypoglossal 

 ■•■ J^ nerve ; X. , foramen for vagus and glosso- 



Of the skull, and origin- P'^^^yngeal nerves ; C.c, carotid canal; 



' o T., tympanic cavity; V., foramen for 



allv consists of four *^i'iseminal nerve ; A.t., auditive tulw ; 



•^ Q., quadrate; Pt., pterygoid ; Q..J.,quad- 



parts — a basilar, two '^''^^-J"sai ■- J- J»8<^i : m., masnia ; pi. , 



■^ ' palatine; F., frontal; L., lachrymal; 



lateral, and a squamous ^■' ''^^^^ = ^ • '""''^''- 

 — grouped around a large opening, the foramen 

 magnum, by which the cavity of the cranium 

 is placed in communication with the vertebral 

 I canal. Immediately below the foramen is a 

 single, rounded condyle for articulation with the 



Fig. 4.— Base of the Skull. 



