130 NEKVOU3 SYSTEM. 



The external strabismus and the immobility of the eye- 

 ball except in an outward direction are due to paralysis of 

 the internal, superior, and inferior recti muscles, the external 

 rectus acting without its antagonist ; a condition which re- 

 quires no further explanation. These points are well illus- 

 trated by the experiment of dividing the nerve in rabbits. 

 If the head of the animal be turned inward, exposing the 

 eye to a bright light, the globe will turn outward, by the 

 action of the external rectus ; but if the head be turned out- 

 ward, the globe remains motionless. 1 



It is somewhat difficult to note the effects of paralysis of 

 the inferior oblique muscle, which is also supplied by the 

 third nerve. This muscle, acting from its origin at the infe- 

 rior and internal part of the circumference of the base of 

 the orbit to its attachment at the inferior and external part 

 of the posterior hemisphere of the eyeball, gives- to the 

 globe a movement of rotation on an oblique, horizontal axis, 

 downward and backward, directing the pupil upward and 

 outward. When this muscle is paralyzed, the superior 

 oblique, having no antagonist, rotates the globe upward and 

 inward, directing the pupil downward and outward. The 

 action of the oblique muscles is observed when we move the 

 head alternately toward one shoulder and the other. In the 

 human subject, when the inferior oblique muscle on one side 

 is paralyzed, the eye cannot move in a direction opposite to 

 the movements of the head, as it does upon the sound side, 

 so as to keep the pupil fixed, and the patient has double 

 vision. 2 



When all the muscles of the eyeball, except the external 

 rectus and superior oblique, are paralyzed, as they are by sec- 

 tion of the third nerve, the globe is slightly protruded, simply 

 by the relaxation of most of its muscles. An opposite action 

 is easily observed in a cat with the facial nerve divided, so 

 that it cannot close the lids. When the cornea is touched, 



1 BERNARD, loc. cit. 



2 LONGET, Traite de physiologic, Paris, 1869, tome iii., p. 556. 



