324 APPENDIX. 



scription of the bones, or skeleton. These constitute the 

 hardest and most enduring portion of the animal system, 

 and on which its form and stability depend. 



In very young animals the bones are, comparatively, 

 soft and yielding, so that many of them may be forced 

 out of their usual forms by slight causes. As the an- 

 imal advances to the adult state, these parts assume a 

 a more solid form, and from a flexible consistence be- 

 come rigid, and many of them even brittle. 



In contemplating this bony skeleton, when it has be- 

 come perfect and fitted for the support of the whole fab- 

 * ric, and the actions of the muscles with which it is every 

 where surrounded, we can not but be struck with the ad- 

 mirable adaptation, and the mutually befitting connection 

 of which its various parts consist. The number of bones 

 in the whole frame amount to about 250, including the 

 teeth. Many of these are connected by surfaces which 

 mutually correspond to each other, as the thigh bone, 

 which has a round head, most perfectly fitted into a semi- 

 spherical socket, having, therefore, free motion in every 

 direction. Others, as the knee-joint, have grooves in the 

 two opposite ends of the bones filling each other, and, 

 therefore, have motion only in two directions. In others, 

 as in the shoulder-blade, and the ribs, the motion is quite 

 limited, there being no proper joint by which it can be 

 effected. 



Articulation. All the bones are connected with each 

 other by what anatomists call articulation. Where 

 motion is required, the evils of friction between the two 

 surfaces are perfectly provided for by the peculiarity of 

 each articulation, the two ends of the bones being cov- 

 ered by soft, elastic cushions, composed of a substance 

 called cartilage, the whole being lubricated by a gelati- 

 nous substance called synovia, which here performs a ser- 

 vice exactlylike thatof oil amongthe wheels of machinery. 



But as the bones must be more or less restricted in their 

 range of motion, there must be some peculiar means by 



What is said of the changes of hones from the young to the adult state? 

 What is said of the adaptation of the bones in forming joints ? What is ar- 

 ticulation ? What is cartilage ? What is synovia ? 



