BONES, MUSCLES, EXEECISE, AND REST. 



245 



and porous, but the external layers are arranged in cells, 

 like a honey-comb. This is the most observable in the heads 

 of the long bones, as in that of the thigh, (Fig. XXXI.) 

 This arrangement gives the bones the greatest strength 

 with the least weight. 



FIG. XXXI. Head of the Thigh Bone sawed open. 



a, a, Outer layer of the bone. 



6, 6, Inner, or honey-comb structure. 



CHAPTER II. 



Skeleton. Number of Bones. Head. Chest. Spine. Verte- 

 brse. Cartilages. Pelvis. 



593; The skeleton (Fig. XXXII.) is .composed of two hun- 

 dred and forty-six bones, including the teeth and the parts of 

 the head* Some of these bones are thin and flat, as the 

 shoulder-blade, (Fig. XXXVII.,) and the parts of the head. 

 21* 



