12 THE VERTEBRAL COLUMN~. [chap, 



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 hcemal arch} I'he 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. 



Fig. 2. — Anterior surface of human thoracic vertebra (fourth), |. c body or centrum ; 

 ?ic neural canal ; p pedicle and / lamina of the arch ; t transverse process ; az 

 anterior zygapophysis. 



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 lamince. The pedicles are usually 

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

 form the sides of the intervertebral forafni7ia 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 

 less open angle. At the point of their junction there is 



^ So called because it encloses the heart and the great central blood- 

 vessels. 



