824 PHYSIOLOGY. 



place to place and in all directions to any objects which he might 

 wish to examine. 



For its part, the motor oculi allows the eye to see particularly 

 objects that are situated high or low or at one side. However, it 

 has a most important function in the harmony of the associated 

 movements by which two images fall upon identical points of the 

 retinae of the two eyes, thus causing but one and the same impression. 



The third pair of nerves manages to regulate the amount of 

 light which falls upon the retina?. Its function in this capacity is 

 to protect the optic nerve against a too intense excitement from 



\ 



Fig. 373. Distribution of the Third and Sixth Nerves in the Orbit. 



( LEVEILLfi. ) 



1, The third nerve. 2, Its superior division. 3, Its inferior division. 4, 

 Branch to the inferior oblique muscle. 5, The sixth nerve distributed to the 

 external rectus muscle. 



excessive light. By contracting the pupil it lessens the pencil of 

 light which penetrates into the depths of the ocular globe. 



On the contrary, it is the sympathetic which produces dilatation 

 of the pupil so that the retina may receive all of the light which can 

 be reflected from obscure objects. For the accomplishment of con- 

 traction and dilatation of the pupil it must be remembered that the 

 iris comprises two kinds of muscular fibers: circular and radiating. 

 The former are connected with the motor oculi; the latter with the 

 sympathetic. 



Finally, the third nerve is considered to have an important 

 function in the act of accommodation. 



