296 



FIFTH PAIR OF NERVES. 



a more particular account of it necessary than 

 would otherwise be required. The chorda tym- 

 pani a delicate filament is given oH from the 

 portio dura shortly before that nerve escapes 

 from tlie aqueduct of Fallopius, behind and be- 

 low the tympanum : it passes upward and for- 

 ward toward the tympanum, contained in a spe- 

 cial canal of the bone, and having reached the 

 back of the chamber it emerges from its posterior 

 wall through a small aperture beneath the base 

 of the pyramid ; it then attaches itself to the 

 outer wall of the tympanum and crosses it 

 toward the anterior, having first received* a 

 delicate filament from the sympathetic, and 

 running forward, upward, and outward. During 

 its course from the posterior to the anterior 

 wall it is situate at first beneath the short crus 

 of the incus, then between the long crus of 

 the incus and the superior part of the handle 

 of the malleus, to which it is connected by the 

 lining membrane of the tympanum. Having 

 ascended above the internal muscle of the 

 malleus it changes its direction and runs down- 

 ward, forward, and inward along the superior 

 anterior part of the circumference of the mem- 

 brana tympani, until it has reached the anterior 

 wall of the chamber, from which it goes out 

 through the Glaserian fissure, along the tendon 

 of the anterior muscle of the malleus. It is 

 throughout excluded from the interior of the 

 tympanum by the lining membrane, which is 

 connected to it upon that side ; it is therefore 

 incorrect to say that it crosses the chamber. 

 After its escape from the tympanum the nerve 

 continues to descend forward and inward in 

 front of the levator palati muscle, and after a 

 course from three-fourths of an inch to an inch 

 long it is attached at a very acute angle to the 

 back of the lingual branch, becomes inclosed 

 in the same sheath with the nerve, and con- 

 tinues connected with it altogether until the 

 nerve has reached the posterior extremity of 

 the submaxillary gland : at that point the 

 chorda tympani divides into two parts, one of 

 which is despatched to the submaxillary gan- 

 glion, and the other continued along with the 

 lingual branch. By somef it is stated that it 

 separates from the nerve at the ganglion, and 

 is altogether ununited to it; this, however, is 

 incorrect. During its descent in company with 

 the lingual branch there may be observed, 

 upon particular examination of the conjoined 

 trunk, a communication and identification be- 

 tween the nervous matter of the two nerves. 



Originally the chorda tympani was regarded 

 as either a recurrent filament of the lingual 

 branch of the fifth or a branch of the portio 

 dura : afterwards the opinion was adopted that 

 it was not a branch of the portio dura, but the 

 cranial superficial petrous branch of the Vidian 

 nerve, which, instead of uniting and being iden- 

 tified with the portio dura, descended through 

 the aqueduct merely in apposition with it or 

 within the same sheath, separated from it again 

 before the nerve escaped from the aqueduct, 

 and constituted the chorda tympani. This view 



* Bock, Mcckcl junior, Cloquct. 

 t Cloquet. 



of the nature of the chord, suggested first, as it 

 would appear, by J. Hunter, has been advo- 

 cated also by Cloquet and Hirzel, and is at 

 present entertained by many in this country at 

 lea>t; it has been objected to by Arnold, and 

 another has been advanced by him from obser- 

 vations made upon the calf and the human 

 subject. Hunter's account of the connection 

 of the nerves is as follows : " This nerve com- 

 posed of portio dura and the branch of the fifth 

 pair sends off, in the adult, the chorda tympani 

 before its exit from the skull, and in the fuetus, 

 immediately after. The termination of the 

 branch called chorda ti/mpani I shall not de- 

 scribe, yet I am almost certain it is not a 

 branch of the seventh pair of nerves, but the 

 last-described branch from the fifth pair," i. e. 

 the Vidian, " for I think I have been able to 

 separate this branch from the portio dura, and 

 have found it lead to the chorda tympani ; per- 

 haps is continued into it ; but this is a point 

 very difficult to determine, as the portio dura 

 is a compact nerve, and not so fasciculated as 

 some others are."* According to Arnold, nei- 

 ther of the previous opinions is correct ; but 

 the petrous nerve anastomoses with filaments 

 of the facial nerve, principally the external, 

 with which it forms a gangliform swelling at 

 the place at which the nerve receives it ; and 

 the branch which forms the corda tympani 

 arises from the gangliform swelling of the racial 

 nerve, and holds in an intimate manner to the 

 petrous nerve ; however it is not to be consi- 

 dered a continuation of the latter: it is united, 

 during its course, to the facial nerve by several 

 filaments, and consequently the chorda tympani 

 ought to be regarded neither as a branch of the 

 facial nerve nor as a continuation of the petrous 

 nerve, but as one composed of both.f Cru- 

 veilhier J maintains that the chorda tympani is 

 not a prolongation of the Vidian nerve, but he 

 assigns no reason for his opinion. The ques- 

 tion at issue probably cannot be decided from 

 the human subject: the impediment opposed 

 to its satisfactory determination by the density 

 of the facial nerve, as admitted by Hunter, and 

 by the manner in which the facial and the 

 Vidian nerves are in it blended together at their 

 junction, will hardly permit the point being 

 accurately ascertained ; but the same diffi- 

 culty does not exist in other animals, and 

 if the disposition of the Vidian nerve at its 

 junction with the facial be examined, in the 

 horse e. g., no doubt will remain that, 1 . the 

 Vidian nerve certainly does not run simply in 

 apposition with the facial nerve, and, 2. the 

 chorda tympani is certainly not a mere conti- 

 nuation of the Vidian nerve. In the horse the 

 facial nerve is much less dense, and more easily 

 analyzed than in man, and at the point of junc- 

 tion with the Vidian its filaments are so free 

 and so loosely connected, that little more is re- 

 quired than to open the packet without violence 

 in order to display satisfactorily the disposition 

 of the Vidian at its junction with the facial : the 



* Animal (Economy, p. 267. 



t Journ. Compl. t. xxiv. p. 339, 341. 



} Anatomic Descriptive. 



