184 PHYSICAL EXPRESSION. 



occiput behind. By referring to the positions and 

 movements of these axes we can define all the 

 positions and movements of the head. 



A. Flexion and extension, i.e. bending forward and 

 backwards of the head, as in nodding. In flexion 

 the antero-posterior axis has its anterior end de- 

 pressed, but the transverse axis remains horizontal, 

 and the two ears remain at the same level. 



In this movement, or posture, symmetry is main- 

 tained. 



B. Rotation, i.e. rotation of the antero-posterior 

 axis in the horizontal plane, the head remaining 

 erect, and the interparietal axis horizontal, without 

 flexion or extension. Such movement may occur 

 in turning the head to look at an object; in this 

 case symmetry is not maintained. Right rotation 

 is used to imply that the forehead moves to the 

 right, as in looking towards the right side. 



C. Inclination, i.e. depression of one or other 

 extremity of the interparietal axis, in which case 

 the ear on the side of inclination is lower than the 

 other. Right inclination means depression of the 

 right extremity of the interparietal axis, or the 

 right ear ; left inclination means depression of 

 the left ear. Inclination is an asymmetrical move- 

 ment ; it may occur without either flexion or rota- 

 tion, but is commonly associated with both. 



The only symmetrical movements of the head 

 are flexion and extension; inclination and rota- 

 tion are asymmetrical movements involving unlike 

 conditions in the two halves of the brain. 



We shall not consider many head movements and 



