5M NERVOUS SYSTEM. 



its operations are rather characteristic of the action of the sympathetic sys- 

 tem and the non-striated muscular tissue. It has been found, also, by Ber- 

 nard, in experiments upon rabbits, that the pupil is not immediately dilated 

 after division of the third nerve. The method employed by Bernard, intro- 

 ducing a hook into the middle temporal fossa through the orbit and tearing 

 the nerve, can hardly be accomplished without touching the ophthalmic 

 branch of the fifth, which produces intense pain and is always followed by a 

 more or less persistent contraction of the pupil. Several hours after the op- 

 eration, however, the pupil is generally found dilated, and it may slowly con- 

 tract when the eye is exposed to the light. In one experiment this occurred 

 after the eye had been exposed for an hour. Farther experiments have shown 

 that although the pupil contracts feebly and slowly under the stimulus of 

 light after division of the motor oculi, it will dilate under the influence of 

 belladonna and can be made to contract by operating upon other nerves. It 

 is well known, for example, that division or stimulation of the fifth nerve 

 produces contraction of the pupil. This takes place after as well as before di- 

 vision of the third nerve. Section of the sympathetic in the cervical region 

 also contracts the pupil, and this occurs after paralysis of the motor oculi. 

 These facts show that the third nerve is not the only one capable of acting 

 upon the iris and that it is not the sole avenue for the transmission of reflex 

 influences. 



Bernard also found that stimulation of the motor oculi itself did not pro- 

 duce contraction of the pupil, but this result followed when he stimulated 

 the ciliary nerves coming from the ophthalmic ganglion. Chauveau, in experi- 

 ments upon horses, did not observe contraction of the pupil following stimula- 

 tion of the motor oculi, although it was sometimes seen in rabbits. At all 

 events, contraction is by no means constant ; and when it occurs, it probably 

 depends upon stimulation of the ciliary nerves themselves or irritation of the 

 ophthalmic branch of the fifth, and not upon stimulation of the trunks of 

 the third pair. When the eye is turned inward by a voluntary effort, the pu- 

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

 strongly, as in looking at near objects, the contraction is very considerable 

 (Miiller). 



The third nerve contains filaments which preside over voluntary move- 

 ments of the ciliary muscle in the accommodation of the eye to vision at dif- 

 ferent distances. 



The following case illustrates, in the human subject, nearly all of the 

 phenomena following paralysis of the motor oculi communis in experiments 

 upon the lower animals : 



The patient was a girl, nineteen years of age, with complete paralysis of 

 the nerve upon the left side. There was slight protrusion of the eyeball, com- 

 plete ptosis, with the pupil moderately dilated and insensible to ordinary 

 impressions 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 paral- 

 lel, 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 deviation upward 



