THE SPINE AS A WHOLE. 71 



is in a man of average height about twenty-eight inches 

 long. Viewed from one side (Fig. 14) it presents four cur- 

 vatures ; one with the convexity forwards in the cervical 

 region is followed, in the dorsal, by a curve with its concav- 

 ity towards the chest. In the lumbar region the curve has 

 again its convexity turned ventrally, Avhilein the sacral and 

 coccygeal regions the reverse is the case. These curvatures 

 give the whole column a good deal of springiness such as 

 would be absent were it a straight rod, and this is farther 

 secured by the presence of compressible elastic pads, the 

 inter vertebral disks, made up of cartilage and connective 

 tissue, which lie between the bodies of those vertebrae 

 which are not ankylosed together, and fill up completely 

 the empty spaces left between the bodies of the vertebrae in 

 Fig. 14. By means of these pads, moreover, a certain 

 amount of movement is allowed between each pair of ver- 

 tebras ; and so the spinal column can be bent to consider- 

 able extent in any direction ; while the movement between 

 any two vertebras is so limited that no sharp bend can take 

 place at any one point, such as might tear or injure other- 

 wise the spinal cord contained in the neural canal. The 

 amount of moveme-nt permitted is greatest in the cervical 

 region. 



In the case of the movable vertebra?, where the arch 

 joins the body on each side, it is somewhat narrowed; this 

 narrowed stalk being known as the pedicle (Ii, Fig. 16), 

 while the broader remaining portion of the arch is its lam- 

 ina. Between the pedicles of two contiguous vertebrae 

 there are in this way left apertures, the intervertebral holes 

 which form a series on each side of the vertebral column, 

 and one of which, Fi, is shown between the two dorsal 

 vertebras in Fig. 10. Through these foramina nerves run 

 out from the spinal cord to various regions of the Body. 

 The sacral foramina, anterior and posterior, are the repre- 

 sentatives of these apertures, but modified in arrangement, 

 on account of the fusion of the arches and bodies of the 

 vertebras between which they lie. 



Sternum. The sternum or breast-bone (Fig. >24 and d, 

 Fig. 13) is wider from side to side than dorso-ventrally. It 



