134 NERVOUS SYSTEM. 



The movements of the iris will be treated of again, in 

 connection with the physiology of vision ; but we may here 

 allude to an interesting fact observed by Miiller, which re- 

 lates to the action of the motores oculorum. When the eye 

 is turned inward by a voluntary effort, the pupil is always 

 contracted ; and when the axes of the two eyes are made to 

 converge strongly, as in looking at near objects, the contrac- 

 tion is very great. 1 



The following case, kindly sent for examination by Dr. 

 Althof, of the New York Eye Infirmary, illustrates, in the 

 human subject, nearly all of the phenomena following pa- 

 ralysis of the motor oculi communis in experiments upon 

 the lower animals : 



The patient was a girl, nineteen years of age, with com- 

 plete paralysis of the nerve upon the left side. There was 

 slight protrusion of the eyeball, complete ptosis, with the 

 pupil moderately dilated and insensible to ordinary im 

 pressions of light. The sight was not affected, but there 

 was double vision, except when objects were placed before 

 the eyes so that the axes were parallel, or when an object 

 was seen with but one eye. The axis of the left eye was 

 turned outward, but it was not possible to detect any devia 

 tion upward or downward. Upon causing the patient to 

 incline the head alternately to one shoulder and the other, 

 it was evident that the affected eye did not rotate in the 

 orbit but moved with the head. This seemed to be a case 

 of complete and uncomplicated paralysis of the third nerve 



Patketicus, vr Trochlearis (Fourth Nerve). 



Except as regards the influence of the motor oculi coin- 

 munis upon the iris, the patheticus is to be classed with the 

 other motor nerves of the eyeball. Its physiology is ex- 

 tremely simple, and resolves itself into the action of a single 

 muscle, the superior oblique. It will be necessary, there- 

 fore, only to describe its origin, distribution, and connections. 



1 MULLER, Elements of Physiology ', London, 1840, vol. L, p. 827. 



