498 SURGICAL APPLIED ANATOMY. [Chap. xxiv. 



The normal curvatures of the column are maintained 

 to a great extent by the intervertebral discs. These 

 substances are twenty-three in number, and make up 

 nearly one-fourth of the entire length of the spine. If 

 the discs be removed, and the vertebrae be articulated 

 in the dry state, the cervical and lumbar convexities 

 almost disappear, and the column tends to present one 

 great curvature, the concavity of which is forwards, 

 and the most marked part of which corresponds to a 

 point just below the middle of the dorsal region. This 

 somewhat resembles the curve seen in the spines of 

 the aged, and in such individuals it may be to no 

 small extent due to the shrinking of the intervertebral 

 discs. 



It is by means of the discs that the movements of 

 the spine are in the main permitted, and it will be 

 found that they are most developed in regions where 

 most movement is allowed. They act also as springs 

 in giving elasticity to the column, and in economising 

 muscular action, while at the same time they play the 

 part of buffers in modifying the effect of shocks trans- 

 mitted along the spine. 



Although the motion permitted between any two 

 individual vertebrae is not extensive, yet the degree of 

 movement capable of being exercised in the column 

 as a whole is considerable. This movement is least 

 free at the dorsal region, and is most extensive in the 

 neck and loins. In the lumbar region (the base of 

 the column) exists the greatest degree of motion per- 

 mitted in the spine, and here is allowed, not only 

 forward and backward flexion, but also lateral bending, 

 and a certain amount of rotation. In the cervical 

 region flexion in the antero-posterior direction is not 

 so ready as it is in the loins, although the neck enjoys 

 the greatest degree of rotation and of lateral flexion. 



Sprains of the vertebral column. The many 

 joints and ligaments of the part, and the varied and 



