ELEMENTS OF PHYSIOLOGY 



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103. A Single Vertebra consists of a thick disk called the 

 body of the vertebra (Fig. 54); behind the disk is an 

 arch, and upon the arch are i 



several projections called pro- 

 cesses. The projection at the 

 rear is called the spinous pro- 

 cess, those at the sides are 

 called transverse processes. 

 All three serve for the attach- 

 ment of muscles which prevent 

 the body from bending 

 forward under its own 

 weight. The holes 

 under the arches of the 

 vertebrae form a passage for 

 the spinal cord. 



. FIG. 54. Thoracic Vertebra 



104. The first cervical (top view). 



Vertebra, Or atlas (Fig. 55), has i, body ; 2, hole which forms part of verte- 



, , . , j bral canal ; 3, spinous process; 4, trans- 



nO body J it has tWO depreS- vers e process ; 5) surface which articulates 



sions into which the occipital ^^^ ^ < sur ' 

 condyles fit. The head rocks 



back and forth (nods) by the condyles slipping in the two 

 depressions, or sockets, of the atlas. The second vertebra 

 (Fig. 56) is called the axis. It has a peg in place of a body ; 

 this peg projects into the hole in the atlas, making a pivot 



joint upon which the atlas and 

 head turn (Fig. 57). When the 

 head moves around, the atlas 

 'moves with it, rotating upon the 

 peg of the axis. Can you find 

 A ^w out why the atlas received its 



FIG. 55. The Atlas (from above), name ? 



105. Between the vertebrae are 

 elastic cushions of cartilage, 

 which give flexibility to the spinal column and prevent injuri- 



a, sockets for articulation with skull ; 

 b, peg of axis.with ligament behind it. 



