THE FRAMEWORK OF THE BODY 



49 



55. Articulations. All unions between bones are called 

 articulations. Some of these allow of more or less move- 

 ment; others permit no movement at all. The bones of 

 the skull, with the exception of the lower jaw and the 

 minute bones belonging to the inner ear, have no motion. 

 In most cases their union is formed by means of toothed 

 edges which fit into each other, forming irregular lines 

 known as serrated sutures. They lessen jar and avert 

 injury to the brain. The different vertebrae of the spine 

 have a very slight motion upon one another, due to the 

 elasticity of the cartilage pads or cushions which sepa- 

 rate them. 



56. Joints, Where two bones are articulated in such 

 a way as to permit one bone to glide freely over the 



Fig. 34. Ball and socket joint at hip. 

 The parts are separated to show attachments of the round ligament. 



other, the union is called a joint. Joints are of vari- 

 ous kinds and are adapted to various movements. 

 MACY'S PHVS. 4 



