38 PI VO T-JOIN TS. 



skull, has been fancifully named the atlas vertebra, after 

 the fabled giant of antiquity who was believed to bear 

 the heavens on his shoulders. It is ringlike in form and 

 the space which it surrounds is separated by a ligament, 

 Z, into a smaller front and larger back division. . In the 

 larger division the spinal cord lies. Into the smaller pro- 

 jects a bony peg (D, Figs. 14 and 15), called from its 

 shape the toothlike or odontoid process, which springs from 



Aa Fas 



D 



Pai 



FIG. 14. 



FIG. 15. 



FIG. 14. The atlas vertebra see i from above. FIG. 15. The axis vertebra, 

 Z/, the ligament which divides tie space surrounded by the atlas into a 'back 

 portion, containing the spinal cord; and a front portion, containing the odontoid 

 process, Z>, of the axis, round which the atlas rolls when we turn the head to either 

 side. 



the second or axis vertebra. Knobs on the under side of 

 the skull fit into the hollows (Fas, Fig. 14) on the atlas: 

 when we turn the face to right or left the atlas, carrying 

 the skull with it, rolls around the odontoid process. 



Another kind of pivot-joint is found in the forearm. 

 Lay the hand and forearm flat on a table, palm upwards. 

 Without moving the shoulder-joint at all, it will be easy 



toid process ? What happens at the joint between atlas and axis 

 when we turn the face to one side ? Where is there another kind of 

 pivot joint? What is the position of radius and ulna when the palm 

 of the hand is turned up ? When turned down ? 



