524 THE THORAX AND VERTEBRAL COLUMN 



rotated and, at the same time, extended. Owing to the 

 coincident occurrence of rotation, the movement of extension 

 produces a lateral curvature instead of a diminution of the 

 normal forward concavity. The vertebral spines lie in the 

 concavity of the curve and, as they are close to the median plane, 

 the apparent amount of lateral curvature, as estimated by 

 examination of the spines, is much smaller than the actual 

 amount. 



In the later stages, the unequal distribution of pressure 

 hinders growth in what was originally the posterior part of 

 the body, and the vertebral bodies become wedge-shaped. 



The direction of the ribs is necessarily affected by the 

 rotation of the thoracic vertebrae. On the convex side of the 

 curve, the ribs produce a " hump " on the dorsal aspect of the 

 body and cause elevation of the scapula and shoulder. On the 

 anterior aspect of the body the ribs are thrust forwards (i.e. on 

 the concave side of the curve). 



The alteration in the shape of the thorax causes a correspond- 

 ing alteration in the shape and position of the viscera which it 

 contains. 



The condition of scoliosis usually occurs in weak children 

 and debilitated adolescents, but it may be congenital or it may 

 follow acute anterior poliomyelitis (cf. p. 494). It can be 

 distinguished from Pott's disease by the absence of muscular 

 rigidity. 



The backward curvature of Kyphosis, which occurs in 

 Pott's disease (p. 519), may be caused by constitutional bone 

 disease or occupational postures. It may also occur in rickets, 

 owing to weakness of the muscles of the back. 



The forward curvature of Lordosis is generally compensatory 

 to flexion at the hip-joint (p. 435). 



The Spinal Medulla (Spinal Cord) begins at the 

 foramen magnum, where it is continuous with the medulla 

 oblongata, and terminates at or just below the lower border of 

 the first lumbar vertebra. In the infant it is relatively longer 

 and extends to the upper border of the third lumbar vertebra. 

 The segments of the spinal medulla are therefore more crowded 

 together than the corresponding vertebrae, and although the 

 nerve-roots pass horizontally to the intervertebral foramina in 

 the upper cervical region, their course within the vertebral 

 canal becomes longer and more oblique in the thoracic region, 

 while the lumbar and sacral nerve-roots descend almost vertically. 



