SIR CHARLES BELL ON THE THIRD PAIR OF NERVES, 227 



the eye, and to none others ; so that it directs the axis of the eye in vision, both 

 controlling the muscles, and having the further property of conveying to the 

 mind the impression of the condition of the muscles. I entertain this idea because 

 it is a double nerve. 



Its origi7i. — Our best authors describe this nerve as arising from the cms 

 cerebri, and so it does, above all the intricacies of the nervous system. It does 

 not enter into the mixture of originating filaments in the pons or nodus. It does 

 not communicate with the decussation in the medulla oblongata. It is in direct 

 communication with the brain. But its precise origin deserves more particular 

 inquiry. 



As I have elsewhere shewn, that the crus cerebri consists of two columns, one of 

 motion, the other of sensation, and that the corpus nigrum divides these columns. 

 If a section be made of the C7ms, just anterior to the origin of the third nerve, we 

 shall find that we cut through the corpus nigrum. And now if we take the cu- 

 rette, and gently divide the two columns, and so separate them in the direction 

 towards the root of this nerve, we shall di\ade or split it, shewing that part of it 

 arises fi-om the anterior column, and part of it from the posterior column. If we 

 carefully dissect and lay out the third nerve, we have a very interesting view, as 

 illustrative of its function, and of the nervous system in general. The roots, as 

 they arise, and for some way in their course (see Plate XIV., Figs. 1 and 2), 

 are in round distinct cords, running parallel to each other. They then join to- 

 gether, and form a dense body, in which the filaments are separated, rejoin, and 

 are matted together, after which their progress is as a common nerve. Their dis- 

 tinct origin from the divisions of the crws — the two distinct fasciculi of parallel 

 fibres — the course of these for some way without exchange of filaments, and 

 then afterwards running into intimate union — are circumstances of much inte- 

 rest, as shewing the distinction of the crus cerebri the distinct nature of the roots 

 of the thu'd nerve, and that it is a double nerve, dedicated to the finer motions 

 of the eye, peculiar in its structure, and yet in conformity with the system which 

 I have followed. * 



A question is naturally suggested here, Is the third nerve a sensitive nerve, 

 as well as a motor ; and if so, how comes it that there is no regular ganglion on 

 the root which it receives from the sensitive column ? 



This would incline me to believe, that the ganglionic root is an organization 

 on the spinal nerves and fifth pair, suited to that sensibility which the body uni- 

 versally and the surface especially enjoys, which gives pain, and becomes a guard 

 upon the fi*ame. 



* Tlie objection which will be naturally suggested, is, that the abducens nerve arises behind the 

 pons. We shall afterwards shew why it does so. And, let it not be forgotten, that the relations of 

 this nerve are the cause of frequent disturbance to the condition of the eye, a consequence, certainly, of 

 its greater complexity- 



