THE FRAMEWORK OF THE BODY 25 



FIG. 9. ELBOW-JOINT. A, Rone of the arm ; B, C, Bones of the forearm 



13. The Spinal Column. The spinal column is often spoken 

 of as "the back bone," whereas in reality it is composed 

 of twenty-four small bones, called vertebrae. These unite below 

 with the sacrum, which forms the base of the pelvis, and upon 

 which the weight of the ttody rests; joined to the lower end 

 of the sacrum is a small bone called the coccyx. The vertebrae 

 are divided into three groups, of which one contains the seven 

 cervical vertebrae, forming the neck, another the twelve dorsal, 

 to which the ribs are attached, and the third the five lumbar, 

 forming what is called the " small of the back." 



The spinal column is a wonderful piece of mechanism It 

 not only connects the important cavities of the body, as has 

 already been shown, but also itself forms a canal, which con- 

 tains the spinal cord. The joints of the vertebrae are remark- 

 able for the thick layers of cartilage which separate the 

 adjacent surfaces of bone. The amount of motion between 

 any two of these bones is not great ; but these little move- 

 ments, taken together, admit of very considerable flexibility, 

 in several directions, without endangering the supporting 

 power of the column. 



J3. Describe the spinal column. 



