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Mr. Bell on the 
sible and instinctive rolling of the eyeball ; and to associate 
this motion of the eyeball with the winking motions of the 
eyelids ; to establish a relation between the eye and the ex- 
tended respiratory system : all tending to the security or 
preservation of the organ itself. 
Of the voluntary nerves. 
The voluntary nerves of the eye are the Third and Sixth. 
The third nerve arises from the crus cerebri, that track of 
medullary matter which gives off all the nerves purely of 
volition. It is given to the muscles of the eye generally, and 
to no part but muscles. For these reasons we retain the 
name motor oculi , given by Willis, although his reasons for 
calling it so were fanciful and unsatisfactory. The Fifth 
nerve, by its ophthalmic division, gives branches to the 
muscles of the eye, but not so profusely as to the surrounding 
parts ; and not more than sufficient to give them sensibility 
in the degree possessed by muscular substance generally. 
Since the branches of this fifth nerve, transmitted to the 
muscles of the eyelids and forehead, do not minister in any 
degree to muscular action there, it would be unwarrantable 
to suppose that they served the purpose of giving action to 
the muscles within the orbit. For these reasons, I conceive 
the Third nerve to be that which gives volition to the muscles 
of the eye, and that it is, of all the nerves of the body, the 
most perfectly and directly under the power of the will. 
The sixth nerve is called abducens, and motor externus. With 
regard to its origin and distribution, there is no obscurity in 
this nerve ; it arises from the same track of medullary matter 
which gives rise to the motor nerves, and it is distributed to 
