NEURO-MUSCULAK MECHANISM 



135 



1. The internal and external recti (IM. and Ex.E.}. 



2. The superior and inferior recti acting along the lines 

 indicated (S.K.}. 



3. The superior and inferior obliques acting in the line 

 (8*b.). 



The internal rectus rotates the pupil inwards. 

 external outwards. 



superior ,, upwards and inwards. 



. ,. . f downwards and in- 



interior 



( wards. 



, r ( downwards and out- 



superior oblique ., 



( wards. 



inferior upwards and outwards. 



S.ob. 



FIG. 64. The left Eyeball in the 

 Orbit, with the Muscles acting 

 upon it. (Man and Ape. ) 



Nose 



In 01. 



S.OL. 



InR. 



InR. 



FIG. 65. The Movements of the Pupil 

 caused by the various Muscles of the 

 Eye. (Right Eye.) (Man and Ape.) 



In the horse, dog, and other similar animals the eye is set 

 more nearly in the axis of the orbit, and the obliques do not 

 pass backwards upon the ball, but act more purely as rotators ; 

 the superior oblique swinging the outer angle of the pupil 

 upwards and inwards, the inferior oblique downwards and in- 

 wards. The superior and inferior recti move the pupil more 

 directly upwards and downwards. 



In the horse and other herbivora a retractor oculi muscle is 

 inserted all round the ball inside these muscles just described, 

 and it can retract the eye in the orbit, and at the same time 

 pushes forward the fatty tissue to which the nictitating mem- 

 brane is attached and thus thrusts this over the front of the eye. 



