HEARING. 553 



part of it. 1 These filaments run partly to the vestibule and semi- 

 circular canals, but especially to the base of the cochlea, where, 

 in the form of a medullary zonula, marked by very elegant 

 plexiform striae, they pass between the two laminse of the sep- 

 tum cochlea? s ," forming according to Mr. Swan, a net-work, and 

 beautifully terminating in a still more fibrous expansion than the 

 optic nerve. 



The facial nerve enters the internal auditory canal in company 

 with the acoustic, which it leaves, and passes through the aqueduct 

 of Fallopius to come out at the foramen stylo-mastoideum. In the 

 aqueduct it gives a filament to the little muscles within the ear. 

 The posterior branch or Vidian nerve of the superior maxillary 

 of the trigeminum, after entering the aqueduct of Fallopius and 

 lying in contact, but not anatomosing with, the facial, gives off a 

 nerve which traverses the tympanum under the name of chorda 

 tympani, and leaves the cranium at the glenoidal fissure. Thus 

 the ear, like the eye and the tongue, has nerves of special sense, 

 of simple sensibility, and of motion. 



Notwithstanding the scrupulous examination of the construc- 

 tion of the organs of hearing by anatomists, very little that if 

 certain is known with regard to the uses of the various parts. It 

 is true that many theories have been advanced, but they have for 

 the most part been founded upon analogies which in the present 

 state of acoustic science will not bear investigation. 



The hypotheses of M. Savart, which have in general been sug- 

 gested by accurate experiments, are the most rational which have 

 hitherto been proposed, and the following are the conclusions at 

 which he has arrived from his experiments. 



1st. That it is not necessary to suppose, as hitherto has been 

 done, the existence of a peculiar mechanism to bring the mem- 

 brane of the tympanum continually in unison with the sonorous 

 bodies which act upon it ; since it is obviously always in those 

 conditions which render it capable of being influenced by any 

 number of vibrations whatever. 2dly. That its tension pro- 

 bably only varies to augment or diminish the amplitude of its 

 excursions, as Bichat had conjectured : this eminent physiologist, 



* " Consult Brendel, Analecta de Concha auris hum-ante. Getting. 1747. 4to. 

 The same, De Auditu in apice conches, Ib. eod. 4to." 



* " Consult Zinn, Observ. Botan. Getting. 1753. 4to. p. 31. sq. 



Scarpa, I.e. tab. viii. fig. 1,2." 



