CHAPTER XXIV. 



THE SPINE. 



THE vertebral column combines in a remarkable 

 way many very different and complicated functions. 

 It acts as the central pillar of the body, and as the 

 column that supports the weight of the head. It 

 connects the upper and lower segments of the trunk. 

 It gives attachments to the ribs. It has the property 

 of mitigating the effects of shocks that are transmitted 

 from various parts of the body. It permits, to a 

 wonderful degree, of a number of most complicated 

 movements ; and, lastly, forms a solid tube for the 

 reception of the spinal cord. 



It owes much of its elasticity, and of its power 

 of breaking up divers forces communicated to it, to 

 its curves. Of the four curves, two, the dorsal and 

 sacral, are primary, are due to the formation of the 

 thoracic and pelvic cavities, and depend mainly upon 

 the shape of the bones. The other two, the cervical 

 and lumbar, are compensatory curves, and depend 

 mainly upon the shape of the intervertebral discs. 

 The dorsal and sacral curves appear in fretal life ; the 

 lumbar and cervical curves appear after birth, and 

 depend on the assumption of the erect position. The 

 infant's spine appears straight. The only marked 

 curve seen in the back of the young child is a general 

 curving of the column backwards, a cyphosis. When 

 the infant is first encouraged to sit erect, this is tho 



