CHAPTER XXIV. 

 THE SKELETON. 



The Two Parts of a Skeleton. Observe that the 

 skeleton as a whole consists of two portions, the axial por- 

 tion, consisting of a central axis, the spinal column, to 

 which the head belongs; and the appendicular portion, 

 the limbs and the bones belonging to them. 



The Uses of the Bones. In the skeleton as a whole 

 observe : 



1. The skeleton shows the form of 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 thorax, 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, or centrum. 



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

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



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 fitted against the vertebrae 

 anterior and posterior to it; 



() The holes in the vertebrae form a passage for the spinal cord ; 



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