THE VERTEBRAL COLUMN 519 



vertebral body is destroyed and collapses, but the posterior 

 part does not give way to the same extent owing to locking of 

 the healthy articular processes. As a result, the part of the 

 vertebral column above the disease is bent forwards on the 

 part below, giving rise to angular curvature (Fig. 157). 



When the disease spreads backwards, the pus may erupt 

 through the periosteum and the posterior longitudinal ligament 

 into the vertebral canal, where it lies outside the dura mater 

 and may compress the spinal medulla. If the disease occurs 

 before the age of five, it is prevented by the neuro-central 

 synchondroses from spreading postero-laterally into the vertebral 

 arch (Fig. 156). 



The periosteal type of the disease affects the anterior surfaces 

 of the bodies of several adjoining vertebrae and results in a 

 gradual collapse, which tends to produce a gentle curvature of 

 the vertebral column rather than a sharp angular curvature. 



Joints at the Upper End of the Vertebral Column. 

 The Atlas, or first cervical vertebra, has no body, and it consists 

 of a short anterior arch and a longer posterior arch, connected 

 to one another on each side by the lateral mass. The superior 

 surfaces of the lateral masses articulate with the condyles of the 

 occipital bone, and at this joint only nodding movements of the 

 head are possible. 



The inferior surfaces of the lateral masses articulate with 

 the superior articular facets of the second cervical vertebra. 

 The Dens (Odontoid Process), which represents the body of 

 the atlas, projects upwards from the body of the second cervical 

 vertebra. Its anterior surface articulates with the posterior 

 surface of the anterior arch of the atlas, and it is held in position 

 by the transverse ligament, which connects the two lateral masses 

 and is separated from the posterior surface of the dens by a 

 small bursa (Fig. 50). 



In rotatory movements of the head, the atlas, which carries 

 the skull with it, moves on the second cervical vertebra. 



Tuberculous disease not uncommonly originates in the 

 body of the second cervical vertebra or in the dens. From the 

 latter situation it may spread forwards and infect the articulation 

 between the dens and the atlas ; or, it may spread backwards 

 and infect the bursa between the dens and the transverse 

 ligament. These joints are supplied by branches from the 

 first and second cervical nerves, which also supply the muscles 

 which rotate the head. Irritation of the branches of these 



