38 SURGICAL APPLIED ANATOMY. [Chap. iv. 



fractures involving the lesser wing of the sphenoid. 

 The third, fourth, and sixth nerves, and the first divi- 

 sion of the fifth, may be affected in cases of aneurism 

 involving the internal carotid artery, where they lie in 

 relation with the cavernous sinus. They may readily 

 be pressed upon, also, by any growth involving the 

 sphenoidal fissure, such as a periosteal node springing 

 from the margin of the fissure, while the sixth nerve, 

 from its more intimate connection with the base of the 

 skull, has been directly torn across in a fracture in- 

 volving that part (Prescott Hewett). 



In paralysis of the third nerve there is 

 drooping of the upper lid (ptosis) ; the eye is almost 

 motionless, presents a divergent squint from unop- 

 posed action of the external rectus muscle, and cannot 

 be moved either inwards, upwards, or directly down- 

 wards. Rotation, in a direction downwards and out- 

 wards, can still be effected by the superior oblique and 

 outer rectus muscles. The pupil is dilated and fixed ; 

 the power of accommodation is much impaired, there 

 is diplopia, and sometimes a little protrusion of the 

 globe from relaxation of the recti muscles. These 

 symptoms refer to complete paralysis of the nerve. 

 In cases of partial paralysis, only one or two of the 

 above symptoms may be present. 



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. 



