in] GENERAL CHARACTERS. 17 



form of a disk or short cylinder. The bodies of contiguous 

 vertebras are connected together by a very dense, tough, and 

 elastic fibrous material, called the interverttbral substance, of 

 peculiar and complex arrangement. This substance forms 

 the main, and in some cases the only, union between the 

 vertebrae. Its elasticity provides for the vertebrae always 

 returning to their normal relation to each other and to the 

 column generally, when they have been disturbed therefrom 

 by muscular action. 



A process (/) rises on each side from the dorsal surface 

 of the body. These meeting in the middle line above form 

 together an arch, surrounding a space or short canal (tic). 

 As in this space lies the posterior prolongation of the great 

 cerebro-spinal nervous axis, or spinal cord, it is called the 

 neural canal, and the arch is called the neural arch, in con- 

 tradistinction to another arch on the ventral surface of the 

 body of the vertebra, called the hcetnal arch. 1 The last is, 

 however, never formed in Mammals by any part of the 

 vertebra itself, but only by certain bones, placed more or 

 less in apposition with it, and which will not here be con- 

 sidered as parts of the vertebral column, strictly speaking. 



The lower portions of each side of the arch (/>), usually 

 thick and more or less vertical in direction, constitute its 

 pedicles. The upper more compressed and more horizontal 

 portions (/) are the lamina. The pedicles are usually 

 notched in front and behind, but most deeply behind, to 

 form the sides of the interrertebral foramina for the trans- 

 mission of the nerves issuing from the spinal cord. Occa- 

 sionally the foramina for these nerves perforate the pedicles, 

 instead of being truly intervertebral. 



The laminae meet in the median line above, at a more or 



1 So called because it incloses the heart and the great central blood- 

 vessels 



