60 



ANATOMY FOE NURSES. 



[CHAP. VI. 



WITHIN 



Seen from the front. 21, superior 

 rectus ; 22, inferior rectus ; 23, ex- 

 ternal rectus ; 24, internal rectus ; 

 25, superior oblique; 26, inferior 

 oblique. 



together by a thin aponeurosis extending over and covering 

 the whole of the upper part of the cranium, are usually known 

 as one muscle, the occipito-frontalis. The frontal portion of this 

 muscle is the more powerful ; by its contraction the eyebrows 



are elevated, the skin of the forehead 

 thrown into transverse wrinkles, and 

 the scalp drawn forward. 



There are about thirty facial mus- 

 cles; they are chiefly small, and con- 

 trol the movements of the eye, nose, 

 and mouth. 



The six muscles which move the 

 FIG. 55. -MUSCLES OF RIGHT eyeball are the four straight or recti, 



EYEBALL WITHIN THE ORBIT. _ ... - . .. 



and the two oblique, muscles. The 

 four recti have a common origin at the 

 bottom of the orbit; they pass straight 

 forwards to their insertion into the 

 eyeball, one, the superior rectus, in the middle line above ; one, 

 the inferior rectus, opposite it below, and one halfway on each 

 side, the external and internal recti. ' The eyeball is completely 

 imbedded in fat, and these mus- 

 cles turn it as on a cushion, the 

 superior rectus inclining the 

 axis of the eye upwards, the in- 

 ferior downwards, the external 

 outwards, the internal inwards. 

 The two oblique muscles are 

 both attached on the outer side 

 of the ball; their action is some- 

 what 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. 



FIG. 56. MUSCLES OF EYEBALL. Seen 

 from side. 19, elevator muscle of eyelid ; 

 22-26, same as in Fig. 55. 



