THE FIFTH CEREBRAL NEEYE. 547 



injury of those filaments of the sympathetic which, after 

 joining the trunk of the fifth, at and beyond the Gasserian 

 ganglion, proceed with the branches of its ophthalmic divi- 

 sion to the iris ; or, as Dr. R. Hall ingeniously suggests, 

 the influence of the fifth nerve on the movements of the 

 iris may be ascribed to the affection of vision in consequence 

 of the disturbed circulation or nutrition in the retina, when 

 the normal influence of the fifth nerve and ciliary ganglion 

 is disturbed. In such disturbance, increased circulation 

 making the retina more irritable might induce extreme 

 contraction of the iris; or, under moderate stimulus of 

 light, producing partial blindness, might induce dilatation : 

 but it does not appear why, if this be the true explanation, 

 the iris should in either case be immovable and unaffected 

 by the various degrees of light. 



Furthermore, the morbid effects which division of the 

 fifth nerve produces in the organs of special sense, make 

 it probable that, in the normal state, the fifth nerve exer- 

 cises some indirect influence on all these organs or their 

 functions. Thus, after such division, within a period 

 varying frori twenty-four hours to a week, the cornea 

 begins to be opaque ; then it grows completely white ; a 

 low destructive inflammatory process ensues in the con- 

 junctiva, sclerotica, and interior parts of the eye ; and 

 within one or a few weeks, the whole eye may be quite 

 disorganized, and the cornea may slough or be pene- 

 trated by a large ulcer. The sense of smell (and not 

 merely that of mechanical irritation of the nose), may be 

 at the same time lost, or gravely impaired ; so may the 

 hearing, and commonly, whenever the fifth nerve is para- 

 lyzed, the tongue loses the sense of taste in its anterior and 

 lateral parts, i.e., in the portion in which the lingual or 

 gustatory branch of the inferior maxillary division of the 

 fifth is distributed.* 



* That complete paralysis of the fifth nerve may, however, be unac- 

 companied, at least, for a considerable period, by injury to the organs 



