44 ANIMAL MECHANICS 



to its length; and, as in man, so in the horse, 

 the greater the muscular power the denser and 

 stronger is the bone. 



The bone not being as a mere pillar, intended 

 to bear a perpendicular weight, we ought not to 

 expect uniformity in its shape. Each bone, ac- 

 cording to its place, bears up against the varying 

 forces that are applied to it. Consider two men 

 wrestling together, and then think how various 

 the property of resistances must be : here they are 

 pulling, and the bones are like ropes ; or, again, 

 they are writhing and twisting, and the bones 

 bear a force like the axle-tree between two w r heels ; 

 or they are like a pillar under a great weight ; or 

 they are acting as a lever. 



To withstand these different shocks, a bone 

 consists of three parts, the earth of bone (sub- 

 phosphate of lime) ; fibres to give it toughness ; 

 and cartilage to give it elasticity. These ingre- 

 dients are not uniformly mixed up in all bones ; 

 but some bones are hard, from the prevalence of 

 the earth of bone; some more fibrous, to resist 

 a pull upon them ; and some more elastic, to resist 

 the shocks in walking, leaping, etc. But to re- 

 turn to the forms : Whilst the centre of the 

 long bones is, as we have stated, cylindrical, their 

 extremities are expanded, and assume various 

 shapes. The expansion of the head of the bone 

 is to give a greater, and consequently a more 



