60 



ANATOMY FOE, NURSES. 



[CHAP. VI. 



the inferior downwards, the external outwards, the internal 

 inwards. The two oblique muscles are both attached on the 

 outer side of the ball ; their action is somewhat complicated, 

 but their general tendency is to roll the eyeball on its own 

 axis, and pull it a little forward and inward. 



The muscles of mastication are the masseter, the temporal, and 

 the external and internal pterygoid. They all have their origin 

 in the immovable bones of the skull, and are all inserted into 

 the movable lower jaw. They generally act in concert, bring- 

 ing the lower teeth forcibly into contact with the upper ; they 

 also move the lower jaw forward upon the upper, and in every 

 direction necessary to the process of grinding the food. 



The chief muscles connecting 

 the tongue and tongue bone to 

 the lower jaw are the genio- 

 glossus and stylo-glossus. They 

 are interesting to us from the 

 fact that during general anaes- 

 thesia they, together with the 

 other muscles, become relaxed, 

 and it is necessary to press the 

 angle of the lower jaw upwards 

 and forwards in order to pre- 

 vent the tongue from falling 

 backwards and obstructing the 

 larynx. 



The most prominent muscle 

 of the neck is the sterno-cleido- 

 mastoid. It is named from its origin and insertion, arising from 

 part of the sternum and clavicle, and being inserted into the 

 mastoid portion of the temporal bone. This muscle is easily 

 recognized in thin persons by its forming a cord-like promi- 

 nence obliquely situated along each side of the neck. It serves 

 as a convenient landmark in locating the great vessels carrying 

 the blood to and from the head. If one of these muscles be 

 either abnormally contracted or paralyzed, we get the deformity 

 called wry neck. 



The muscles of the trunk may be arranged in three groups : 

 (1) muscles of the back ; (2) muscles of the thorax ; (3) muscles 

 of the abdomen. 



FIG. 57. MUSCLES OF THE TONGUE. 



