26 ANATOMY AND PHYSIOLOGY. 



CHAPTER III. 



THE BONES. 



OF all the parts of the body, the bones require to be first con- 

 sidered, because they form the frame-work whereon all the soft parts 

 are fixed, and determine the shape and size of the whole. They 

 are 'the hardest and most durable part of the body, and are found 

 existing ages after all the rest has long mouldered into dust. This 

 hardness and durability depend on the large proportion of inor- 

 ganic matter which enters into the composition of bony tissue, the 

 great quantity of lime which is mingled in it. The animal and 

 earthy parts of bone can be easily separated and demonstrated in a 

 separate state. If a piece of bone be immersed for a day or two in 

 diluted muriatic acid, the earthy part will be completely dissolved 

 out, and the animal part will be left, yet the bone will still have the 

 same size and the same shape, so intimately are the two different 

 materials blended together, and may be tied in a knot as represented 

 in the following figure. If it be now dried and weighed it will 



be found to have lost nearly two-thirds of its original weight, the 

 loss consisting of the earthy particles. The substance now ob- 

 tained is the cartilage of bone, which is very nearly the same in 

 composition as the cartilages which we find ready formed by nature 

 in the body. It is much softer than bone, but harder than any of 

 the other soft parts ; it is highly elastic, and if compressed or bent, 

 speedily regains its original shape. When dried, it assumes a 

 darker color, and becomes hard and tough, translucent, and very 

 like horn. When boiled, this substance is nearly all dissolved, 



