THE SKELETON. 7 



you will find a part of it, like a cinder, among the 

 ashes. This is the mineral part. The fire has 

 burned out the animal matter. Take the "drum- 

 stick" bone of a chicken and place it in a bottle con- 

 taining a mixture made by filling the bottle half full 

 of water and adding about half as much muriatic 

 acid a common drug which you can get for a trifle 

 at the nearest drug store. This will take out the 

 mineral matter from the bone and leave the animal 

 matter. The mineral matter which you took from 

 the fire was brittle or crumbling. The animal 

 matter, when taken from the acid, is gluey and can 

 be wound, like a cord, about the finger. The broad 

 or flat bones, like those of the head, are not entirely 

 solid. Between the two outside layers of such a bone 

 there is a layer of spongy-like material. These 

 three layers of structure in a flat bone can be clearly 

 seen hy looking at the edge of such a bone which 

 has been sawed through. 



The long bones are generally hollow and contain 

 a substance called marrow. At the ends they are 

 usually thicker and more spongy. This serves to 

 break the force or shock of heavy stepping or jump- 

 ing with the lower limbs, or a hard stroke with the 

 arm. The ends of the long bones are also covered 

 with a smooth, white substance called cartilage. 

 This aids in giving the bone an easy motion at the 

 joint where it is united to another bone. 



