THE SPINAL COLUMN 



13 



Cervical 

 vertebrae 



Thoracic 

 vertebrae 



Spinal Column. The fundamental part of the skele- 

 ton and the only part possessed by some of the lower 

 forms of vertebrates is the backbone called the spinal or 

 vertebral column. The spinal column varies in form 

 from the simple rod of gristle found in some of the lowest 

 vertebrates, to the many jointed flexible bony structure 

 which distinguishes the higher species. 



Vertebrae of the neck. In man, the vertebral column 

 consists of 31 short bones, the vertebra?. These verte- 

 brae vary in form accord- 

 ing to their position in 

 the spine and the work 

 which they have to do. 

 For example, to permit the 

 head to turn and bend 

 in various directions, the 

 vertebras in the neck must 

 move freely. They are there- 

 fore comparatively small 

 and loosely connected by 

 strong bands of gristle, 

 the ligaments, and firmly 

 held by strong contractile 

 bands, the muscles. Move- 

 ment beyond a certain 

 amount is checked by the 

 ligaments which at the flf/" Sacrum 

 danger point become tense. 

 As a result, dislocation of 

 the bones of the neck is 

 rare. To allow the head 

 to nod, the upper or first of the neck vertebra is so 

 shaped as to permit the lower portion of the skull 

 which rests upon it to slip readily. To permit the 



Lumbar 

 vertebrae 



Coccyx 



1'ia. 9. The spinal column, right lateral 

 view and dorsal view. (Testut.) 



