OUR BONES ARE LIVING LEVERS 



55 



When we look at the atlas (fig. 12) we see that it is 

 merely a ring made up of three of the parts — the right 

 and left arches and the fourth element, — but the body is 

 missing. A glance at fig. 12, B, will show what has be- 

 come of the body of the atlas. It has been joined to the 

 central block of the second vertebra — the axis — and pro- 

 jects upwards within the front part of the ring of the 

 atlas, and thus forms a pivot round which rotatory move- 

 ments of the head can take place. Here we have in the 

 atlas an approach to the formation of a wheel — a wheel 

 which has its axle or pivot placed at some distance from 

 its centre, and therefore a complete revolution of the 



FRONT ARCH 



SIDE ARCH 



Fig. 12. — A, The original parts of the first or atlas vertebra. B, Showing the 

 "body" of the first vertebra fixed to the second, thus forming the pivot on 

 which the head turns. 



atlas is impossible. A battery of small muscles is attached 

 to the lateral levers of the atlas and can swing it freely, 

 and the head which it carries, a certain number of degrees 

 to both right and left. The extent of the movements is 

 limited by stout check ligaments. Thus, by the simple 

 expedient of allowing the body of the atlas to be stolen 

 by the axis, a pivot was obtained round which the head 

 could be turned on a horizontal plane. 



Nature thus set up a double joint for the movements 

 of the head, one between the atlas and axis for rotatory 

 movements, another between the atlas and skull for 

 nodding and side-to-side movements. And all these 

 she increased by giving flexibility to the whole length 



