10 



APPLIED ANATOMY. 



FIG. 14. Transverse section of the skull showing- its 

 variations in thickness at different points. 



cells likewise appear at puberty and increase with age. At birth, they are repre- 

 sented by simple cancellous bone. 



THE SKULL IN ADULTS. 



As the child grows, the bones of the face increase more rapidly than do those 



of the vault. The bony prominences become marked, due to the action of the 



various muscles of mastication, expres- 

 sion, etc., inserted into them. The 

 face is much larger in size in proportion 

 to the calvarium than was the case in 

 infancy. While in infancy bone is prac- 

 tically homogeneous, in late childhood 

 and early adult life cavities begin to 

 develop in it. 



Outer and inner tables of compact 

 tissue are formed, separated by diploic 

 structure. The frontal, ethmoidal, and 

 other air-sinuses are an exaggeration 

 of these diploic spaces. They are lined 

 with mucous membrane and communi- 

 cate with the nasopharynx. The diploe 

 first begins to appear about the age of 



ten years, but is not well formed until early adult life. It contains large veins, 



called the diploic veins, which communicate with the veins both of the inside and 



outside of the skull. In injuries to the skull 



bleeding from these veins is rarely trouble- 

 some and usually stops spontaneously. 



The skull is thinner in the white than 



in the negro race. It is thickest over the 



occipital protuberance and mastoid proc- 

 esses. The bone is thinnest in the temporal 



and lower occipital regions. The two tables 



are separated widely from one another in 



the region of the frontal sinuses. 



Tables. The inner table is thinner and 



more brittle than the outer one, and in frac- 

 tures it is almost always more extensively 



splintered than the outer. In rare cases the 



outer table may be temporarily depressed by 



a glancing blow and spring back into place 



without showing any depression, while the 



inner table may be fractured. 



The two tables are not exactly parallel. 



Where the skull is thin, as in the temporal 



and occipital regions, they are close to- 

 gether; where it is thick, they are farther 



apart. The outer surface of the skull is 



comparatively even and smooth. The inner 



surface is quite uneven, being depressed in 



places to receive the convolutions of the 



brain. For this reason it is necessary to use 



the trephine with great care, as it may cut 



through on one side of the circle and injure 



the dura mater before it cuts through the 



other part. 



The sutures of the skull begin to ossify 



at about the age of forty years and continue to fuse until about the eightieth year. 

 Frontal Sinuses. The frontal sinuses begin to develop at the age of seven 



years, but do not increase rapidly in size until puberty. When adult age is reached 



FIG. 15. Frontal sinus of one side; the anterior wall 

 has been cut away, exposing its interior. 



