CHAPTER III. 

 THE SKELETON. 



The skeleton * of the human body is composed of 

 three materials : lone, cartilage, and connective tissue. 



The bones form the main supporting framework of the 

 body, and determine its shape ; they provide levers on 

 which the muscles moving the body pull, and are arranged 

 so as to surround cavities in which soft, delicate organs, 

 as brain, spinal cord, and heart, may lie in safety. 



Cartilage finishes off many bones at joints, forming 

 elastic pads with smooth surfaces \, it is also used instead 

 of bones in some parts of the skeleton where considerable 

 flexibility is required. Cartilage affords one of the best 

 tissues of the body for the examination of intercellular 

 substance. A thin slice of it highly magnified, Fig. 7, 

 shows the cartilage cells, a, ~b, scattered through an almost 

 structureless material. Very young cartilage consists of 



Of what is the skeleton made up ? What functions do the bones 

 fulfill ? Where is cartilage found ? What are its purposes ? What 

 is seen when a thin slice of cartilage is highly magnified ? Of what 

 does young cartilage consist. 



* There are two kinds of skeleton met with in the animal kingdom ; the external 

 skeleton or exoskeleton, and the internal skeleton or endosketeton. The exoskeleton 

 is made by the skin, either in it or on it ; examples are found in the shells of clams 

 anu lobsters : the scales of fishes and snakes ; the tortoise-shell of turtles ; the 

 feathers of bird 5 *; the hair and claws of beasts. In man the exoskeleton is only 

 Slightly developed, hair, uaiis and teeth belong to it. 



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