THE SKELETON 



FIG. 56. The Axis 

 (side view). 



a, one of the areas for 

 articulation with atlas ; 

 6, pivot or peg. 



. b 



FIG. 57. 

 a, atlas ; b, axis ; c, pivot of the axis. 



a - 



ous jarring of the brain and spinal cord. Otherwise, the head 

 would receive a great shock whenever one alighted upon the 

 feet in jumping from a height. The spinal column is 



so constructed 



as to furnish 



strength to sup- 

 port the body, 



to facilitate the 



attachment of 



the organs to it, 



to furnish a safe 



passage for the 



spinal cord, 



yet while accomplishing these several 

 purposes, to allow the body to bend without displacing 

 any of the numerous organs 

 of the trunk. 



106. The Thorax, or chest, 

 is formed in the rear by the 

 twelve thoracic vertebrae ; in 

 front, somewhat parallel to 

 the spinal column, but ap- 

 proaching it above, is the 

 sternum, or breastbone (Fig. 

 58). Twelve ribs curve 

 around each side. Each rib 

 joins one of the thoracic 

 vertebrae behind. The first 

 seven pairs directly join the 

 sternum in front by means 

 of short cartilages, and are 

 called true ribs. The next 

 three pairs, called false ribs, 

 do not reach the sternum, 

 but each rib unites to the rib 



-10 



I -" 



FIG. 58. Bony Walls of Thorax. 



a, b, vertebral column; c, sternum; d, costal 

 cartilages; e, united cartilages of 8th, gth, 

 and loth ribs; n, 12, floating ribs. 



