THE SKELKTON 



Skeleton Tissues. The tissues employed in the con- 

 struction of the skeleton are the osseous, the cartilaginous, 

 and the connective tissues. These are known as the sup- 

 porting tissues of the body. They form the bones, supply 

 the elastic pads at the ends of the bones, and furnish 

 strong bands, called ligaments, for fastening the bones 

 together. The skeleton forms about 16 per cent of the 

 weight of the body. Its tissues, being of a more durable 

 nature than the rest of the body, do not so readily decay. 

 Especially is this true of the osseous tissue, which may be 

 preserved indefinitely, after removal from the body, by 

 simply keeping it dry. 



The Bones. The separate units, or parts, of which the 

 skeleton is constructed are called bones. They are the 

 hard structures that can be felt in all parts of the body, 

 and they comprise nearly the entire amount of material 

 found in the prepared skeleton. As usually estimated, 

 the bones are 208 in number. They vary greatly in size 

 and shape in different parts of the body. 



Composition and Properties of Bones. The most notice- 

 able and important properties of the bones are those of 

 hardness, stiffness, and toughness. Upon these properties 

 the uses of the bones depend. These properties may, in 

 turn, be shown to depend upon the presence in osseous 

 tissue of two essentially different kinds of substance, 

 known as the animal matter and the mineral matter. If a 

 bone is soaked in an acid, the mineral matter is dissolved 

 out, and as a result it loses its properties of hardness and 

 stiffness. (See Practical Work.) This is because the min- 

 eral matter supplies these properties, being composed of 

 substances which are hard and closely resemble certain 

 kinds of rock. The chief materials forming the mineral 

 matter are calcium phosphate and calcium carbonate. 



