240 ANATOMY OF VERTEBRATES. 



contributed by the lining of the tympanum, and an outer layer by 

 that of the auditory passage. The proper membrane, moreover, 



is divisible into two layers, an outer one 



186 • • 



consisting of fibres radiating from near 

 the centre, and an inner, thicker, less 

 distinctly fibrous layer, but indicative 

 of a contrary disposition of such fibres. 



Membrana tympani and. malleus, nat. The COnSpicUOUS radiating fibrCS 1WSS 

 size; Human, a outer, b inner view. „ . A . _ ° l 



trom the circumference of the mem- 

 brane to be fixed to the handle of the malleus. They show no 

 characters of voluntary muscular fibre. 



Anthropotomy distinguishes the following parts of the otos- 

 teals: — in the hammer, 'malleus,' fig. 166, a; a, head; b, arti- 

 cular surface (adapted to b of the incus) ; c, neck ; d, handle ; 

 e, short process; f, long process: this latter is the most con- 

 stant, and is called simply the ' process ' in comparative anatomy ; 

 sometimes also ' Rau's process,' from the describer of its true 

 shape and flattened end in Man : in the anvil, ( incus,' B ; a, body ; 

 b, articular surface ; c, short crus ; d, long cms ; c, lenticular 

 process, epiphysis, or ossicle : in the stirrup, ' stapes,' d ; a, head ; 

 b, neck ; c, anterior crus ; d, posterior crus ; D, the base. The 

 head of the malleus is lodged in the roof of the tympanum above 

 the upper margin of the membrane, and sends its ' handle ' down 

 to near its centre, as seen from without at «, from within at b, 

 fig. 186. The body of the incus lies in the upper and back part 

 of the tympanum; its articular surface is directed forward, the 

 joint with the malleus being a synovial one, with articular car- 

 tilage and a fibrous capsule : the short crus is directed backward 

 towards the mastoid cells ; the long crus descends almost parallel 

 with the handle of the malleus, to articulate by means of the 

 lenticular process with the head of the stapes, fig. 178. 



Savart's experiments ! show that the malleus participates in the 

 oscillations of the tympanic membrane ; that they are propagated 

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

 ovalis. Two muscles, probably subserving volitional impulse 

 through their proper nervous supply, act upon the otosteals ; and 

 from vibrations of the drum-membrane to which those bones are 

 attached, they may be excited to act, also, automatically. The 

 ( musculus internus mallei,' or 'tensor tympani,' fig. 167, e, arises 

 from the eustachian process of the alisphenoid, and from a groove 

 in the bony part of the eustachian tube, and passing backward 

 forms a slender tendon, which enters the tympanum, bending at 



