290 
Mr. Bell on the 
Of the function of the ophthalmicus , a division of the fifth nerve. 
We are, in the first place, to inquire by what nerve the 
common endowment of sensibility is bestowed upon the 
membranes and surfaces of the eye. On recurring to this 
subject we are reminded, that the sensibilities of the body 
differ as much in kind as in degree ; that the sensation of 
pain is provided 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 preceding paper, by experiment, 
that on dividing the branch of the fifth nerve to the cheek 
and lips, the skin was deprived of sensibility, although in 
possession of other nerves, and enjoying muscular activity. 
The same has been proved in regard to this ophthalmic di- 
vision ; for if that branch of it which comes through the orbit 
and mounts upon the forehead, be divided, the skin will be 
deprived of sensibility. 
These facts are so strong, that when supported by the 
symptoms of disease they afford no apology for deep dissec- 
