8oo 



THE MEMBRANA TYMPANI. 



handle of the malleus, which is attached to it ; while the short process of the 

 malleus slightly bulges out the membrane near its upper margin (figs. 577, 584). 



Structure -The tympanic membrane consists of three layers :-(l) The membrana propria 

 is a fibrous membrane with radial fibres on its outer surface, and circularly arranged fibres on 



its inner aspect. (2) The 

 surface directed towards the 

 meatus is covered with a thin 

 and semi-transparent part of 

 the cutis. (3) The side to- 

 wards the tympanum is cover- 

 ed with a delicate mucous 

 ^ x membrane, with simple squa- 

 mous epithelium. Numerous 

 nerves and lymph-vessels, as 

 well as inner and outer blood- 

 vessels, occur in the mem- 

 brane. 



[The middle layer, or 

 substantia propria, is fixed 

 to a ring of bone, which 

 is deficient above. It is 

 filled up by a layer com- 

 posed of the mucous and 

 Fig. 581. Fig. 580. cutaneous layers called 



Fig. 579. Tympanic membrane with the auditory ossicles (left) the membrana flaccida, or 

 seen from within. Ci, incus; Cm, malleus ; Ch, chorda tym- Shrapneli's membrane. 1 



-Qr>Vii+Qr>T^ Vict * J 



[Examination. When ex- 



Ci, incus ; Cm, malleus 

 pani ; T, jwuch-like depression (after Urbantschitsch). Fig. 

 580. Tvnii>anic membrane and the auditory ossicles (left) seen 



M, manubrium amining the outer ear and 



from within, i.e., from the tympanic cavity, 

 or handle of the malleus ; T, insertion of the tensor tympani 

 h, head ; IF, long process of the malleus ; a, incus, with the 

 short (K) and the long (/) process ; S, plate of the stapes ; 

 Ax, Ax, is the common axis of rotation of the auditory ossicles ; 

 S, the pinion-wheel arrangement between the malleus and 

 incus. Fig. 581. Tympanic membrane of a new-born child 

 seen from without, with the handle of the malleus visible on it. 

 At, tympanic ring with its anterior (v) and posterior (h) ends. 



membrana tympani, pull the 

 auricle upwards and back- 

 wards. The membrana tym- 

 pani is examined by means of 

 an ear speculum (fig. 582). 

 The speculum is placed in 

 the- ear, and light is re- 

 flected into it by means of a 

 concave mirror, perforated in 

 the centre, and having a focal distance of four or five inches. It is convenient to have the 

 mirror fixed to a band placed round the head, as in the case of the laryngoscopic reflector 

 (fig. 359). It is important to remember that the membrane is placed obliquely, so that the 

 posterior and upper parts are nearer the surface. The membrane m health is greyish in colour 

 and transparent, so that the handle of the malleus is seen running from 

 above downwards and backwards, while at the anterior and inferior part 

 there is a cone of light with its apex directed inwards. ] 



Function. The tympanic membrane catches up the sound- 

 waves which penetrate into the external meatus, and is set into 

 vibration by them, the vibrations corresponding in number and 



amplitude to the vibrating movements of the air. Politzer 

 connected the auditory ossicles fixed to the tympanic membrane 

 Oof a duck with a recording apparatus, and could thus register 

 the vibrations produced by sounding any particular tone. Owing 

 to its small dimensions, the tympanic membrane can vibrate 

 Oin toto, to and fro in the direction of the sound-waves correspond- 

 ing to the condensations and rarefactions of the vibrating air, and 

 therefore executes transverse vibrations, for which it is specially 

 Ear specula of adapted, owing to the relatively slight resistance, 

 various sizes. Fundamental Note. Stretched strings and membranes are 



generally only thrown into actual and considerable sympathetic vibration when 

 they are affected by tones which correspond with their own fundamental tone, or 



