THE BONES. 23 



that of the spine is the most striking. It is firm, and yet 

 elastic. It is capable of carrying a great weight, and yet 

 easily bent in any direction. It is made up of a number of 

 separate bones, and yet in its centre there is formed a perfect 

 canal throughout nearly its whole length, just as a continuous 

 canal is formed by placing a number of spools evenly one 

 upon another. The main portion of the spine consists of 

 twenty-four separate and distinct pieces, and these rest upon 

 one large solid mass of bone called the sacrum. In early 

 life, the five bones which form the sacrum are separate; so 

 also are the four small bones beneath these, which in. adult 

 life unite and form one bone. In infancy there are, there- 

 fore, thirty-three bones in the spine, and in the adult only 

 twenty-six. 



The individual bone is called a vertebra, hence the whole 

 is sometimes called the vertfil>ral column. Kach separate 

 vertebra consists of a solid "piece of bone called the body, 

 and projections (processes) running outwards and backwards. 

 Those running backwards incline towards each other and soon 

 unite, so as to form the canal for the spinal cord. It then 

 continues backwards for varying lengths at different parts of 

 the spine, and is called the spinous process. This is why the 

 vertebral column is sometimes called the spine. These are 

 the various projections of bone we feel immediately under the 

 skin, from the back of the neck downwards. The other pro- 

 jections run out sidewise, and are for attachment of long, 

 slender muscles to strengthen the whole column, very much 

 in the same way as ropes strengthen and support the masts 

 of a ship. 



The bodies of the vertebrae are placed one upon another, 

 with a layer of elastic cartilage between, as bricks are placed 

 one above another, with mortar between. They are not 

 cemented firmly together, as is the case in a brick wall ; the 

 cartilage, being elastic like rubber, allows the bones to bend 



