OSSICLES OF THE EAR. 209 



bearing upon tins point. Artillerists are in danger of rup- 

 ture of the membrana tympani from sudden concussions. 

 To guard against this injury, it is recommended to stop the 

 ear, draw the shoulder up against the ear most in danger, and 

 particularly to inflate the middle ear after Valsalva's method. 

 " This method consists in making a powerful expiration, with 

 the mouth and nostrils closed." 1 



Mechanism of the Ossicles of the Ear. The ossicles of 

 the middle ear, in connection with the muscles, have a two- 

 fold function : First, by the action of the muscles, the mem- 

 brana tympani may be brought to different degrees of ten- 

 sion. Second, the chain of bones serves to conduct sonorous 

 vibrations to the labyrinth. It must be remembered that the 

 handle of the malleus is closely attached to the membrana 

 tympani, especially near its lower end. Near the short pro- 

 cess, the attachment is looser and there is.even an incomplete 

 joint-space at this point. The long process is attached closely 

 to the Glasserian fissure of the temporal bone. 



The malleus is articulated with the incus by a very pecul- 

 iar joint, which has been accurately described by Helmholtz. 

 This joint is so arranged, presenting a sort of cog, that the 

 handle of the malleus can rotate only outward ; and when a 

 force is applied which would have a tendency to produce a 

 rotation inward, the malleus must carry the incus with it. 

 This mechanism has been aptly compared by Helmholtz to 

 that of a watch-key with cogs which are fitted together and 

 allow the whole key to turn in one direction, but are sepa- 

 rated so that only the upper portion of the key turns when 

 the force is applied in the other direction. 2 In the articula- 



1 TROLTSCH, Diseases of the Ear, New York, 1869, p. 148. According to Dr. 

 Roosa, rupture of the tympanic membrane has been very seldom observed in 

 soldiers during the late war in this country, though it is well known that it 

 sometimes occurs, even from the report of a pistol near the ear. (RoosA, Dis- 

 eases of the Ear, New York, 1873, p. 223.) 



2 HELMHOLTZ, Mechanism of the Ossicles of the Ear and Membrana Tympani, 

 New York, 1873, p. 32, et seq. 



