86 



outward to either side of the head, behind the ear. 

 They are so attached to the bottom of the skull, 

 near to and on each side of its articulation with 

 the spine, that they either draw the head down 

 toward the breast-bone, or the breast-bone up- 

 ward toward the head, according as the resisting 

 lines of the spine, as developed in the neck, are 

 brought forward or backward between the two 

 muscles, and so by their positions give the pre- 

 ponderating leverage one way or the other. That 

 is to say, if the plane of junction of the two C C 

 of the neck S be well thrust forward between the 

 stemo-mastoids, the action of these muscles will 

 raise the breast-bone ; whereas, if this be retired, 

 the same action will lower the head. 



Suppose the chest well raised and filled with 

 air, and the neck fully gathered by the " super- 

 imposition " of the diagonal counter-actions (§ 71), 

 the plane of junction between its two C C will be 

 advanced, and fi*om this position every change of 

 bearing in the head articulation will alter the 

 drawing of the sterno-mastoids at the upper cor- 

 ners of the breast-bone, whether of both equally 

 or of one preponderatingly. Thus a perfect action 

 of the neck is all important to perfect inovement. 



§ 87. The sterno-mastoids must partake of the 



