on the Structure, Distribution, and Functions of the Nerves. 357 



we are reminded, that the sensibilities of the body differ as 

 much in kind as in degree ; that the sensation of pain is pro- 

 vided to rouse our activity, and guard us against violence, or, 

 by means more direct, to excite instinctive motions, which 

 shall anticipate the most rapid actions of the will, and serve as 

 a more perfect safeguard. The trigeminus, or fifth nerve, 

 bestows upon all the surfaces of the head and face, external 

 and internal, that sensibility which is enjoyed by the rest of 

 the body through the spinal nerves. But through some of its 

 branches is also bestowed that distinct sense on certain parts 

 for the purpose of drawing the muscles into combination ; as, 

 for example, that fine sensibility of the surface of the eye to 

 the presence of minute particles, which at once excites the 

 flow of tears, and draws the muscles into a combination to 

 expel the offensive matter. 



It has been shown in a former paper, that the division of a 

 branch of the fifth nerve distributed to the cheek and lips, de- 

 prived these parts of their sensibility, although they remained 

 in possession of other nerves, and continued to enjoy muscu- 

 lar activity. The same has been proved in regard to this 

 ophthalmic branch ; if that branch of it which comes through 

 the orbit and mounts upon the forehead, be divided, the skin 

 will be deprived of its sensibility. Whence it is allowable to 

 infer, that this is the case with the ophthalmic branch of the 

 same nerve also ; but not to rest upon inference alone, the 

 symptoms of disease both render deep dissection in the living 

 animal unnecessary, and authorise the conclusion ; for a case 

 was communicated to the author by Mr. Crampton, of Dublin, 

 which he has adduced in part, and which appears to justify 

 the inference sufficiently. 



" A few days after the discharge from the ear had ceased, 

 the eye became entirely insensible to the touch. This loss of 

 feeling extended to the* lining of the eye-lids, to the skin co- 

 vering them, and to the skin of the cheek and forehead, for 

 about an inch surrounding the eye : it did not go beyond the 

 middle line of the face. When she told me her eye was dead 

 (as she expressed it), to be certain, I drew my finger over its 

 surface ; and so far was this from giving her pain, that she 

 assured me she could not feel that I was touching it at all. 

 The eye-lids made no effort to close while I was doing this, 

 but the conjunctiva appeared sensible to the stimulus, as a 

 number of vessels on the surface of the eye became immedi- 

 ately injected with blood." It is only necessary to remark, in 

 order to understand the inference, that the ophthalmic nerve 

 in question goes through the orbit, supplying the parts 

 that are contained in it, and extends its branches to the angle 



of 



