30 



ANATOMY FOR NUKSES. 



[CHAP. IV. 



muscular attachment. The flat bones are composed of two thin 

 layers of compact tissue, inclosing between them a variable 

 quantity of cancellous tissue. In the bones of the skull this 

 outer layer is thick and tough ; the inner one thinner, denser, 

 and more brittle. The cancellated tissue lying between the 

 two layers, or "tables of the skull," is called the diploe. 

 Flat bones of the head : 



Occipital ............. 1 



Parietal ............ . . 2 



Frontal .............. JL 



4 



The occipital bone is situated at the back and base of the 

 skull. At birth the bone consists of four parts, which do not 

 unite into a single-bone until about the sixth year. The internal 

 surface is deeply concave, and presents many eminences and de- 



pressions for the 

 reception of parts 

 of the brain. 

 There is a large 

 hole the fora- 

 men magnum - 

 in the more in- 

 terior portion of 

 the bone, for the 

 transmission of 

 the medulla ob- 

 longata, the en- 

 larged portion of 

 the spinal cord. 



The- parietal 

 bones (paries, a 

 wall) form by 

 their union the 

 FIG. 24. PARIETAL BONE. Inner surface. A, parietal de- s j c l es a,^ roof of 

 )>i<->sion; E, furrow for ramification of arteries. 



the skull. The 



external surface is convex and smooth ; the internal surface is 

 concave, and presents eminences and depressions for lodging 

 the convolutions of the brain and numerous furrows for the 

 ramifications of arteries. 



