NERVES OF THE BRAIN. 239 



respondence, though in opposite conditions, the one contracted, the other re- 

 laxed. 



And now as to the motions of the eye, we cannot be surprised if the mus- 

 cle exterior to the eyelids, and the muscle lying deep in the socket should be re- 

 lated in the condition of relaxation and contraction, and that the relation should 

 be established through the connection of their respective nerves at their roots — 

 this is the matter to be enquired into. 



Let us now attend to the relation of the lesser portion of the orbicular mus- 

 cle — ^that paler set of fibres which lies on the eyelids. 



When we recollect that the margins of the eyelids in closing, touch only at 

 their outer edge, and that when closed, a gutter is left between them and the 

 cornea, the winking of the eye, far from clearing the surface of the cornea, would 

 suffuse it, by leaving the tear upon it, were it not that in the act of winking the 

 eyeball is turned up. It is by this revolving of the ball, that the cornea is moist- 

 ened and wiped clear. 



How is this revolving motion of the eyeball accomplished ? No action of the 

 eyelids could produce this effect. It can only be done by the action of superior 

 rectus or inferior oblique. It is not performed by the superior rectus, which I 

 determined, by cutting that muscle in a monkey, when the upward rolling of 

 the cornea continued accompanying the effort of the eyelids to close. 



The two oblique muscles being opponents, the relaxation of the upper one 

 will give power to the lower one, so that we have, as before, to seek for a relation 

 between the paler fibres of the orbicularis and the superior oblique. The supe- 

 rior oblique stands in the same relation to the internal and paler circle of the 

 orlicularis that the abducens or rectus externus does to the stronger exterior circle 

 of the same muscle. 



Thus brought to acknowledge the relation between the muscle seated on the 

 eyelid and external, to a muscle seated deep in the orbit, and seeing no direct 

 connection between them, we must turn once more to notice the relations which 

 establish the connection at the roots or origins of their respective nerves. 



By such study of the muscular apparatus of the eye, and their actions for 

 the protection of the organ, we are following out the principle, that the structure 

 and action of a part will direct us to the peculiarity of its nerves. That the eye 

 stands distinguished from the other organs of sense by the multiplicity of its 

 guards, is owing to its extreme delicacy of structure, and its necessary exposure. 



In my second paper, I had occasion to notice that the facial nerve, or portio 

 dura of the seventh, coming circuitously through the foramen stylo-mastoideum to 

 supply the face, is the nerve also of the orbicularis palpebrarum, or, in other 

 words, of the exterior muscles of the eyelids. It was also noticed, that the/«- 

 cialis at its origin is in direct relation with the sixth or abducens nerve. Now, 

 this sixth nerve takes a dhect course forwards into the bottom of the eye-socket, 



