COMPOSITION OF BONES. 147 



also outwards and inwards, as when sitting 1 on 

 horseback or with the legs crossed. The socket 

 being- much deeper than that of the shoulder-joint, 

 the thigh-bone has not the same range of motion as 

 the humerus, but it has proportionally greater secu- 

 rity. 



The patella or knee-pan / is well known. It is a 

 small bone, constituting the projection of the knee. 

 It increases the power of the muscles which extend 

 the leg, and protects the front of the knee-joint. 

 The tibia m is the principal bone of the leg, and is 

 the only one articulated with that of the thigh. Its 

 lower end forms the projection at the inner ankle. 

 The fibula n is the long slender bone at the outer 

 side of the leg, the lower end of which forms the 

 outer ankle. The tibia and fibula both contribute to 

 the formation of the ankle-joint, which, like that of 

 the knee, is almost limited to flexion and extension. 

 The tarsal bones constituting the foot display an 

 admirable mechanism, but without plates any de- 

 scription of them would be unintelligible. My pres- 

 ent aim being practical utility, I shall therefore pass 

 over these details, and rather lay before the reader 

 several considerations of a more general and directly 

 useful nature. 



Bones consist of two kinds of substances, viz. 

 those of an animal and those of an earthy nature. 

 To the former belongs every thing connected with 

 the life and growth of bones, and to the latter the 

 hardness and power of resistance by which they are 

 characterized. 



The animal portion of bones constitutes, accord- 

 ing to the analysis of Berzelius, about 32.17 per cent, 

 of their substance, and consists chiefly of albumen, 

 gelatine, cellular membrane, blood-vessels, nerves, 

 and absorbents. Of the remaining 67 per cent, of 

 earthy matter, nearly 52 parts consist of phosphate, 

 and 11 of carbonate, of lime. The relative propor- 

 tions of the animal and earthy constituents vary, 



