MOTOR OCULI OOMMTJNIS. 129 



paralysis in the human subject. Heroert Mayo was one of 

 the first to experiment upon this nerve in animals living or 

 just killed, but his observations were made chiefly with ref- 

 erence to the movements of the iris. 1 Bernard, 3 Longet, 8 

 and all others who have divided the nerve in living animals, 

 are agreed with regard to the phenomena following its sec- 

 tion, which depend upon paralysis of the voluntary muscles. 

 These phenomena are as follows : 



1. Falling of the upper eyelid, or blepharoptosis. 



2. External strabismus, immobility of the eye, except 

 outward, inability to rotate the eye on its antero-posterior 

 axis in certain directions, with slight protrusion of the eye- 

 ball. 



3. Dilatation of the pupil, with a certain amount of in- 

 terference with the movements of the iris. 



The falling of the upper eyelid is constantly observed 

 after division of the nerve in living animals, and always fol- 

 lows its complete paralysis in the human subject. An ani- 

 mal in which the nerve has been divided cannot raise the lid, 

 but can approximate the lids more closely, by a voluntary 

 effort. In the human subject, the falling of the lid gives to 

 the face a very peculiar and characteristic expression. The 

 complete loss of power shows that the levator palpebrse su- 

 perioris muscle depends upon the third nerve entirely for its 

 motor filaments. In pathology, external strabismus is very 

 frequently observed without falling of the lid, the filament 

 distributed to the levator muscle not being affected. 



1 MAYO, Anatomical and Physiological Commentaries, Number ii., London, 

 1823, p. 6 ; and, Outlines of Human Physiology, London, 1827, p. 294. 



2 BERNARD, Lecons sur la physiologic et la pathologic du systeme nerveux, Paris, 

 1858, tome ii., p. 204, et seq. 



Bernard gives the following directions for division of the third nerve in the 

 rabbit : A small steel hook is introduced along the external wall of the orbit 

 into the middle temporal fossa. With the hook the nerve is caught at the ante- 

 rior extremity of the fold of the dura mater, which is attached to the sella tur- 

 cica, and torn across. In this operation, there are generally evidences of pain 

 from the ophthalmic branch of the fifth as it is touched by the instrument 



* Loc.ciL 



