THE BONES AND JOINTS. 17 



CHAPTER II. 

 THE BONES AND JOINTS. 



SECTION I. 1. The bones are the framework of the 

 body. When joined, as in the living man, they constitute 

 the skeleton. They serve three purposes: 



1. They give the body shape and firmness of outline. 

 The soft parts which cover them add grace. 



&. They act as levers by which the muscles attached 

 to them move the body. 



s. They protect important organs. 



2, There are two main cavities in the body formed 

 wholly or in part by the skeleton; viz., 



1. The cavity of the skull and spinal column. The 

 skull contains the brain, and is a tight box whose w r alls 

 are strong, and which is so shaped as to resist great press- 

 ure. There are no openings into it except those small 

 ones through which blood-vessels and nerves pass in and 



SUGGESTIONS TO TEACHERS. 1. Every school in which anatomy and 

 physiology are taught ought, if possible, to have a human skeleton. Lack- 

 ing this, the next best thing is to have the skeleton of some quadruped. 

 The general resemblance will be sufficient to make it a good illustration of 

 the text. If you have no complete skeleton, get dried bones, beef-bones, 

 mutton-bones, vertebrae, long bones, jaw-bones. Have them sawed in dif- 

 ferent directions. Much can be learned from them. The differences be- 

 tween dried bone and fresh, living bone must, however, be borne in mind. 

 The experiments of softening a bone by maceration in weak hydrochloric 

 acid for a few weeks, and of removing the animal matter by burning, are 

 easily tried. 



2. The different parts of a joint can be shown in a sheep's leg. 



