THE BACK. 89 



Although the vertebrae of the different groups differ 

 more or less in size and shape in accordance with the 

 various demands of their positions, they all have certain 

 general characteristics. Each has a body, two laminae, two 

 pedicles, two transverse processes, and one spinous pro- 

 cess. The pedicles extend back from the body on either 

 side and support two broad plates of bone, the lamince, 

 whose juncture at the back completes the spinal foramen 

 for the passage of the cord. At their juncture is the 

 spinous process, which can be felt beneath the skin, while 

 the transverse processes project from the juncture of the 



FIG. 32. A type of vertebra. (Leidy.) 1, Body; 2, pedicle; 3, lamina; 4, 

 spinal foramen; 5, spinous process; 6, transverse process; 7, articular process. 



laminae with the pedicles. All the processes are for the 

 attachment of muscles that move the spine. The body 

 is formed of cancellous bone with a compact layer outside. 

 Transversely it is slightly oval, while its upper and lower 

 surfaces are flat, except in the crevical region, where the 

 upper surface is concave laterally and the under convex 

 laterally and concave from before back. Between the 

 bodies are disks of fibro-cartilage, which increases motion 

 and springiness. The spinous process or spine is short 

 in the cervical region, long and directed downward in the 

 dorsal region, thick and projecting almost straight out in 

 the lumbar region. The pedicles are notched above and 

 below so that when articulated the notches of two verte- 



