CHAPTER II. 

 THE BONES. 



The Two Parts of a Skeleton. The skeleton consists of 

 two portions, (i) the central axis,} or spinal column, to 

 which the head belongs ; and (2) the limbs and the bones 

 belonging to them. 



The Uses of the Bones. i. The skeleton gives the form 

 to the body. 



2. It supports the softer tissues. 



3. It protects softer parts, as the brain in the skull, the 

 spinal cord in the spinal column, the heart and lungs in 

 the chest, etc. 



4. The bones serve as levers in producing motion and 

 locomotion. 



Study of a Vertebra. Take a vertebra from the middle of the spinal 

 column : 



1. Its most solid part is its body. 



2. On the dorsal side of this is the neural arch, forming with the 

 body the neural ring, through which the spinal cord passes. 



3. From this arch there extend projections, or processes. Hold the 

 vertebra by the tip of its longest process, and place it beside the cor- 

 responding vertebra in the complete skeleton. Note that : 



(a) The body is flattened where it fits against the vertebras above 

 and below it ; 



(b} The holes in the vertebras form a passage for the spinal cord ; 



(c) The middle projection is the spinous process, and the series of 

 spinous processes form the ridge of the backbone ; 



62?) The two side projections are the transverse processes. 



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