Chap, iv.j THE ORBIT AND EYE. 47 



In paralysis of the fourth nerve there is often 

 but little change to be seen, since the function of the 

 superior oblique muscle, supplied by this nerve, may, 

 in part, be performed vicariously. " There is usually 

 only very slight defect in the mobility of the eye \ 

 what there is occurs chiefly in the inner and lower 

 angle of the field of vision ; there is deviation of the 

 eye inwards and upwards on lowering the object, 

 and simply upwards when it is turned far towards 

 the healthy side " (Erb). In any case there will be 

 diplopia, especially in certain positions of the globe. 



In paralysis of the sixth nerve there is con- 

 vergent strabismus, with consequent diplopia, and an 

 inability to rotate the eye directly outwards. 



Sometimes all the oculo -motor nerves of the eye 

 are paralysed, and in such cases the lesion is probably 

 situated either at their nuclei of origin or at the 

 cavernous sinus, in the wall of which the nerves lie 

 close together. 



In paralysis of the first division of the fifth 

 there is a loss of sensation in all the conjunctiva, except 

 such as covers the lower lid (supplied by the palpebral 

 bi'anch of the infraorbital nerve), loss of sensation in 

 the globe, and in the skin supplied by the supratrochlear 

 and supraorbital nerves, and in the mucous and cuta- 

 neous surfaces supplied by the nasal nerve. No reflex 

 movements (winking) follow upon irritation of the 

 conjunctiva, although the patient can be made to wink 

 on exposing the eye to a strong light, the optic nerve 

 in this case transmitting the impression to the facial 

 nerve. Sneezing also cannot be excited by irritating 

 the mucous membrane in the anterior part of the nose. 

 Destructive ulceration of the cornea may follow thi.s 

 paralysis, due partly to damage to the trophic branches 

 contained in the paralysed nerve, partly to the anaes- 

 thesia which renders the part readily injured, and 

 partly to the loss of the reflex effect of the sensory 



