426 STUDIES IN ADVANCED PHYSIOLOGY. 



from the motores occuli reach the muscles of accommoda- 

 tion and the muscles of the iris. It is this latter nerve 

 which in a reflex way causes the contraction of the pupil 

 when the eye is subjected to an increased amount of light. 

 It is interesting to note that a contraction or relaxation 

 of the muscles of the iris is never confined to one eye alone, 

 but that both eyes move in unison. It is evident, there- 

 fore, that the motores occuli of the right and left eye are in 

 direct anatomical communication with each other at or near 

 their place of origin. Fibers from this same nerve control 

 the muscles of the upper eye-lid. That this nerve is the 

 most important motor nerve of the eye may be readily seen 

 from its innervation, and a section of the nerve induces at 

 once the relaxation and closing of the upper eye-lid ; the 

 impossibility to move the ball of the eye, a dilatation of the 

 pupil, and the impossibility of a contraction of the same 

 even when subjected to a strong light, and finally a paral- 

 ysis of the accommodation of the eye so that the focus of 

 the eye is immovably set for distant objects. 



Fourth. The pathetici. The pathetici leave the brain 

 immediately anterior to the pons Varolii, innervate the su- 

 perior oblique muscles and so help to control the move- 

 ments of the eye in so far as they are affected by these 

 muscles. The cutting of the patheticus nerve seems to 

 show no immediate results in the eye, but an animal so 

 treated is unable to fix its gaze upon a certain point when 

 its head is turned. By the paralysis of the superior oblique 

 muscle the eyeball affected is rotated along with the head. 

 In this way the two eyes are not directed to the same point 

 and a double vision occurs. 



Fifth. The trigeminales . The fifth pair of nerves, the 

 trigeminales, contain both motor and sensory fibers. They 

 arise from the medulla each in two roots, the smaller of 

 which contains the motor fibers which arise from centers in 

 the floor of the fourth ventricle, while the larger is sensory. 

 This larger root before joining the motor one passes 

 through the large Gasscrian ganglion. The sensory fibers 



