444 Anatomy Applied to Medicine and Smgery. 



and this flow tends to wash away the offending body, but 

 this action, however, would be interfered with. Another 

 means by which nature attempts to remove an offending 

 body from the conjunctiva is the contraction of the orbicu- 

 laris palpebrarum, whereby the eyelids, in closing, would 

 mechanically dislodge it, but if there be no warning given 

 on account of the paralysis of the sensory nerves supply- 

 ing the conjunctiva, there would be no reflex act of 

 winking. The reflex act, in winking, follows a path 

 through the sensory branch of the ophthalmic to the sen- 

 sory nucleus, thence to the nucleus for the third nerve and 

 from the latter, through the facial, totheorbicularis palpe- 

 brarum. Lastly, herpes, also, may develop along the in- 

 tegumentary distribution of this nerve. 



Sixth nerve. Injury to this nerve causes a paralysis 

 of the external rectus muscle and hence there is resultant 

 inability to abduct the eyeball, so that the unopposed in- 

 ternal rectus draws it inwards, i.e., adducts it, producing 

 convergent strabismus and, therefore, double vision. It 

 is interesting to note, in connection with the sixth nerve, 

 that, just as the facial carries fibres belonging to the third 

 nucleus, so the third nerve carries fibres belonging to the 

 sixth nucleus, and these fibres, so carried by the third 

 nerve, are decussatory fibres from the sixth nucleus, which 

 go to the opposite internal rectus muscle. Normally, 

 when a patient is asked to turn his eyes to the right, the 

 right eye is turned by the action of the external rectus 

 and the left eye by the action of the internal rectus, since 

 both these muscles are supplied by the one nucleus, viz., 

 the sixth, and so, in an injury to the right sixth nu- 

 cleus, the patient could not carry either the right or left 

 eye towards the right, and the same holds good for the left 

 eye. 



