DEVELOPMENT OF THE SKELETON. 



281 



tlic intervertebral discs (liganienta inter vertehr alia), and 

 at the same time, are connected by joints, so that the 

 entire vertebral column forms a firm and solid axis, which 

 is, however, flexible and elastic, capable of moving freely 

 in all directions. In the various regions of the trunk, 

 the vertebrae diff*er in form and connection, so that the 

 following are distinguished in the human vertebral column, 

 beginning from above : seven neck- vertebrae, twelve breast- 

 vertebrae, five lumbar-vertebrae, ^yq cross-vertebrae, and 

 four to five tail-vertebrae. The uppermost, those directly in 



iJV||^^ 



Fig, 254. — Third neck-vertebra of man. 

 Fig. 255. — Sixth breast. vertebra of man. 

 Fig. 256. — Second lumbar-vertebra of man. 



contact with the skull, are the neck -vertebrae (Fig. 254), 

 and are distinguished by a hole found in each of the 

 two lateral processes. There are seven neck-vertebrae in 

 Man, as in nearly all other Mammals, whether the neck 

 is long, as in the Camel and the Giraffe, or sliort, as in the 

 Mole and the Hedo-ehoof. The fact that the number of these 

 neck-vertebrae is always seven, — and there ^ are but few 

 exceptions (explicable by adaptation), — is a strong argu- 

 ment for the common descent of all Mammals ; it can only 

 be accounted for as a strict transmission from a common 



