92 INNERVATION. [CHAP. XVin. 



in thickness is attached, so that the adherent part shall extend from 

 the circumference to the centre of the membrane, while the free 

 portion may project beyond the circumference. When a vibrating 

 glass is brought near this membrane, very regular figures are pro- 

 duced, modified, however, by the adhesion of the piece of wood, and 

 the vibrations of the membrane are communicated to the wood, on 

 which likewise regular figures may be produced. The more exten- 

 sive the membrane, the longer and thicker may be the piece of wood 

 in which it can excite oscillations, and Savart states that, with 



Fig. 146. Fig. 147. 



membranes of a considerable diameter, he has produced regular vi- 

 brations in rods of glass of large dimensions. The oscillations of 

 the piece of wood are much more distinct when the adherent por- 

 tion is thinned down, as in c, d, fig. 147, by which it becomes more 

 completely identified with the membrane ; the oscillations of this 

 latter are communicated directly to the thinned portion of the wood, 

 and thence propagated to the thick portion, a: sand spread upon a 

 will exhibit active movements, and will indicate very distinct nodal 

 lines. Hence it may be inferred, that the malleus participates in the 

 oscillations of the tympanic membrane; and these vibrations must be 

 propagated to the incus and stapes, and thus to the membrane of 

 the fenestra ovalis. The chain of ossicles then evidently performs 

 the office of a conductor of oscillations from the membrana tympani 

 to the membrane of the fenestra ovalis ; but the malleus likewise 

 has the important function under the influence of its muscles of re- 

 gulating the tension of the tympanic membrane ; and to allow of 

 the changes in the position of this bone necessary for that purpose, 

 we find it articulated with the incus by a distinct diarthrodial joint, 

 and between this latter bone again and the stapes there exists 

 another and a similar joint. This mobility then of the chain of 

 bones, and the muscular apparatus of the malleus and stapes have 

 obvious reference to the regulation of the tension of the membrane 

 of the tympanum as well as of that of the fenestra ovalis. 



We have already seen how the muscle of the malleus regulates the 

 membrana tympani, increases its tension, and thus limits the extent 



