37 S Drum cf the Ear. [Book IX. 



vafcular membrane. The tympanum communicates 

 Tvith the cavity of the fauces, by means of the meatus 

 auditorius internus, or Euftachian tube. This canal, 

 which is partly bony and partly cartilaginous, begins by 

 a very narrow opening at the anterior and almoft fupe- 

 rior part of the tympanum, increaling in fize as it 

 advances towards die cavity of the fauces, where it 

 terminates by an oval Opening behind the noftrils. 



Within the tympanum are lodged the little bones of 

 the ear, which are four in number, and from their 

 form have received the following names. i. The 

 malleus or hammer, a. The incus or anvil. 3. The 

 roundifh or oval bone, 4. The ftapes or ftirrup. 



The body of the malleus is placed in the upper 

 part of the tympanum, and a long procefs, called 

 the handle, defcends between the lamins of the 

 membrana tympani, where it is accurately fixed. It 

 is articulated with the incus by means of two project- 

 ing ridges and a furrow betweea them. 



The incus, which cpnfifts of a body and two legs, 

 and is not unlike a tooth with a double root, exceeds. 

 the other little bones of the ear in fize and ftrength. 

 Its body is connected with the malleus ; its fhorter 

 leg is placed at the entrance of the canal, which leads 

 to the cells of the maftoid procefs j its longer leg 

 takes the fame direction with the handle of the mal- 

 leus, to which it is attached by a ligament, and being 

 bent inwards at' its termination, receives the fmall 

 oval bone, and by means of this is united to the 

 ftapes. 



The refemblance of the ftapes to a ftirrup is fo 

 ftrong, that it can fcarcely efcape obfervation. Its 

 bead, which is formed by the union of its two legs, is 

 hollowed for the reception of the little oval bone which 

 connects it with the longer kg of the incus. The two 



legs 



