FIFTH PAIR OF NERVES. 



309 



more remarkable, has been reported by Mr. 

 Bishop,* in which the functions of the fifth 

 nerve seemed altogether obliterated by the 

 pressure of a diseased growth within the 

 cranium, and yet the patient saw distinctly 

 to the last, the only derangement which oc- 

 curred in the function of vision being the loss 

 of the power of distinguishing colours, which 

 appears sufficiently accounted for by a certain 

 degree of pressure exerted by the tumour upon 

 the optic nerve. Magendie endeavours to 

 support his views upon this and other points 

 connected with the properties of the nerve by 

 reference to a case reported by Serres, which 

 appears very inadequate, and will be discussed 

 by-and-bye. 



Influence of the fifth nerve on hearing. 

 The great affinity between the sense of hearing 

 and that of touch renders it more easy to 

 conceive how hearing might be excited through 

 the medium of the fifth nerve. As we have 

 seen that the ocular nerve in certain animals is 

 a branch of the fifth nerve, so is the auditory. 

 Among the cartilaginous fishes there are several 

 instances in which this occurs. The origin of 

 the auditory nerve from the fifth in fishes was 

 first announced by Scarpa,f and by him sup- 

 posed to apply to fish generally. This view 

 is combated by Treviranus :J it is admitted 

 in part by Serres; he states that in osseous 

 fishes the auditory nerve is united at its in- 

 sertion with the fifth; in cartilaginous fishes, 

 that the auditory is sometimes confounded 

 with the fifth, sometimes separated distinctly 

 enough, as in the raia clavata. From his own 

 observations the writer would say, that in the 

 bony fishes the two nerves cannot be said to 

 be united or to arise the one from the other, 

 but only to have a common superficial attach- 

 ment to the medulla oblongata ; and from the 

 analogy of the same nerves in the higher classes 

 of animals, he would not admit, without 

 further proof, a common superficial attachment 

 as establishing identity of ultimate connection 

 with the encephalon. As to the cartilaginous 

 fishes, it appears to him that Serres has fallen 

 into an error with regard to the connection of 

 the auditory nerve. It appears to the writer 

 that the fifth and the auditory are con- 

 founded in the raia clavata as plainly as in 

 any other individual of the class ; the posterior 

 ganglionic fasciculus of the fifth and the 

 auditoiy nerve form one trunk for a distance 

 of some lines after leaving the medulla ob- 

 longata ; they are at all events enclosed within 

 the same sheath : but whether they are to be 

 regarded as branches of a common trunk or 

 not, it is difficult to decide. The weight of 

 naalogy is certainly opposed to a conclusion 



* Medical Gazette, vol. xvii. 



t De Auditu et Olfactu. 



$ Journ. Compl. 



Serres seems to have overlooked the fact that 

 there exist two ganglionic fasciculi in the raia 

 clavata ; that he has assumed the anterior fasci- 

 culus to be the fifth, and described the posterior, 

 with which the auditory is connected, as the auditory 

 and facial nerves : the error will be manifest upon 

 tracing the distribution of the fasciculus. 



in the affirmative ; and, though this were ad- 

 mitted, a difference between the auditory and 

 the other branches of the fifth (as supposed) 

 must still be admitted, inasmuch as the auditory 

 separates from the nerve before the occurrence 

 of the ganglion, and has not itself a ganglion. 

 On the other hand the auditory may be se- 

 parated from the rest of the nerve, after the 

 division of the common investing membrane, 

 with little or no laceration of fibres. Still it 

 may be asked why, if they be distinct nerves, 

 are they united into one trunk? The opinion 

 that the fifth nerve holds an important in- 

 fluence over the sense of hearing derives support 

 from the circumstance, that in most, if not 

 all, the cases of disease of the nerve, the 

 sense of hearing becomes impaired, though 

 not obliterated. 



The last question proposed to be considered 

 with reference to the functions of the fifth 

 nerve is its connection with nutrition. 



The opinion that the nerve controls the 

 nutrition of the parts which it supplies has 

 been advocated by Magendie, more particularly 

 with regard to the eye. It has been already 

 stated that we are indebted to this writer for 

 information in regard to results of the division 

 of the entire trunk of the nerve within the 

 cranium. Of these the most prominent is 

 the entire loss of sensibility on the same 

 side of the face, and in regard to the eye 

 especially, loss of sensibility in the conjunc- 

 tiva, upon which the most irritating chemical 

 agents then produce no impression. These 

 immediate effects of the section were followed 

 by others not less remarkable: on the next 

 day the sound eye was found inflamed by 

 the ammonia, which had been applied to it, 

 while the other presented no trace of inflam- 

 mation. Other changes, however, supervene. 

 The cornea of the eye of the side on which 

 the section is made, twenty-four hours after- 

 wards begins to become opaque ; after seventy- 

 two it is much more so ; and five or six days 

 after it is as white as alabaster. On the second 

 day the conjunctiva becomes red, inflames, 

 and secretes a puriform matter. About the 

 second day the iris also becomes red and in- 

 flames, and false membranes are formed upon 

 its surface. Finally the cornea ulcerates, the 

 humours of the eye escape, and the globe 

 contracts into a small tubercle. In endeavouring 

 to ascertain the cause of these changes, Ma- 

 gendie, on the supposition that they might 

 be owing either to the continued exposure of 

 the eye to the air or to the want of the 

 lachrymal secretion, divided the portio dura 

 in one rabbit, the effect of which is to destroy 

 the power of closing the eyelids; and from 

 others he cut out the lachrymal gland; but 

 in neither case did opacity of the cornea suc- 

 ceed. The sequence of the effects mentioned 

 after the section of the nerve might naturally 

 lead us to infer that the loss of nervous in- 

 fluence gives rise to them. But such is not 

 the inference drawn by Magendie, nor indeed 

 can it be admitted : absence or subtraction 

 of an influence cannot be directly the cause 

 of an alteration in the condition of an object 



