138 NERVOUS SYSTEM. 



pain. The same experiments illustrate the function of the 

 nerve, inasmuch as its irritation is followed by powerful con- 

 traction of the muscle and deviation of the eye outward. 

 Division of the nerve in the lower animals or its paralysis 

 in the human subject is attended with internal, or converg- 

 ing strabismus, from the unopposed action of the internal 

 rectus muscle. 



"With regard to the associated movements of the eyeball, 

 it is a curious ftict that all of the muscles of the eye that 

 have a tendency to direct the pupil inward or to produce 

 the simple movements upward and downward ; viz., the in- 

 ternal, inferior, and superior recti, are animated by a single 

 nerve, the motor oculi communis, this nerve also supplying 

 the inferior oblique ; and that each muscle that has a ten- 

 dency to move the globe so as to direct the pupil outward, 

 except the inferior oblique ; viz., the superior oblique and 

 the external rectus, is supplied by a special nerve. The 

 various movements of the eyeball will be studied more 

 minutely in connection with the physiology of vision. 



