Proceedings of Public Societies. 



1824.] 



certain pajts, for tlic purpose of draw- 

 ing the int. ,icl»;s into combination; as 

 for cxamplo, that fine sensibilily oftlic 

 surface of the eye to the presence of 

 minute particles, which at once ex- 

 cites the flow of tears, and draws the 

 muscles into a combination to expel the 

 offensive matter. 



The respiratory nerve of the face 

 performs two offices; one of vvhicli is 

 voluntary, as in moving the cheeks 

 and lips in speech; and the other in- 

 voluntary, as in moving the nostrils 

 in breathing during sleep or insensi- 

 bility. In like manner that branch of 

 the respiratory nerve which is pro- 

 longed to the eyelids, performs a doa- 

 ble office, contracting the eyelids by 

 volition, and also producing those 

 involuntary winking motions of the 

 eyelids which disperse the tears, and 

 preserve the lucid surface clear. 



The voluntary nerves of the eye are 

 the third and sixth. TJie 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 tiie eye gene- 

 rally, and to no part but muscles. 

 The fdth 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 sufTicicnt to give thctn sensibility 

 in the degree possessed by muscular 

 substance generally. 



The .sixth nerve is called abducens, 

 and motor cxternus. 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 a voluntary 

 muscle, the rectus externus. In this 

 iX'Bpcct it is like a subdivision of the 

 third, and without doubt it is a volun- 

 tary nerve ; but there is a circum- 

 stance in its connection which I can- 

 not explain. It receives a gross 

 branch from the great visceral nerve 

 called sympathetic. This nerve, as- 

 ccmling througii the base of the skull, 

 unites with the sixtii nerve as it is cn- 

 l<'ring the orbit. These nerves, the 

 third and sixth, although they receive 

 no external impression, arc neverthe- 

 less agents which give rise to the per- 

 ceptions of place or relation, in aid of 

 that sensibility enjoyed by the optic 

 iiiTVi; and retina. 



In our books of Anatomy, the nerves 

 are nundjerod according to the method 

 of Willis, au arrangement which was 



55 



made in ignorance of the distinct 

 functions of the nerves, and merely in 

 correspondence with the order of suc- 

 cession in which they appear on 

 dissection. 



The first nerve is provided with a 

 sensibility to effluvia, and is properly 

 called the olfactory nerve. 



The second is the optic nerve, and 

 all impressions upon it excite only 

 sensations of light. 



The third nerve goes to the muscles 

 of the eye solely, and is a voluntary 

 nerve by which the eye is directed to 

 objects. 



The fourth nerve performs the 

 insensible traversing motions of the 

 eyeball. It combines the motions of 

 the eyeball and eyelids, and connects 

 the eye with the respiratory system. 



The fifth is the universal nerve of 

 sensation to the head and lace, to the 

 skin, to the surfaces of the eye, the 

 cavities of the nose, the mouth and 

 tongue. 



'J'he sixth nerve is a muscular and 

 voluntary nerve of the eye. 



The seventh is the auditory nerve, 

 and the division of it, called portiu 

 dura, is tiie motor nerve of the face 

 and eyelids, and the respiratory nerve, 

 and that on which the expression of 

 the face depends. 



The eighth, and (he accessory nerve, 

 arc respiratory nerves. 



The ninth nerve is the motor of the 

 tongue. 



The tenth is the first of the spinal 

 nerves; it has a double root and a 

 double office ; it is both a muscular 

 and a sensitive nerve. 



Had I taken the nerves of any other 

 complex organ rather than of the eye, 

 I shoidd have had an easier task. If 

 I had taken t!ie nerves of the tongue, I 

 should have been able to prove by ex- 

 periment, and in a iTiauncr the most 

 tlirect, that the three nerves belong to 

 three distinct functions, and stand 

 related to three dill'erent classes- of 

 parts. I could have shown tiiat taste 

 and sensibility belong to the office of 

 the lif'th nerve, voluntary motion to 

 the ninth, and deglutition to the 

 glosso-pliaryngral nerve of the fongue. 

 If we turn to the opini(jns which 

 have been entertained on tix; subject 

 of the brain and nerves, we find one 

 theory to ha\e prevailed from the 

 Creek authors to the lime of Willis, 

 and to have descended liom him with 

 little alteration, to modern writers. 

 The bvuiu has bocu supiiosud to se- 



crctc 



