406 TYMPANIC CAVITY AND CHAIN OF BONES. 



of the nasal cavity (n, fig. 200) by a canal termed the Eusta- 

 chian tube (k, fig. 204). The partial or complete closure of 

 this tube, occasioned either by swelling of its lining membrane 

 or by the viscid secretion from it, produces the slight deafness 

 common among those who are suffering from " colds." Within 

 the cavity of the tympanum, there is a very curious apparatus 

 of small bones and muscles, which serves to establish a con- 

 nexion between the membrane of the drum and the small 

 membrane covering the entrance to the internal ear. These 

 bones are four in number ; and are termed the malleus or 



Fig. 202. BONES OF Fig. 203. CAVITY OF THE TYMPANUM, WITH 



THE EAR. THE BONES IN THEIR PLACES. 



hammer (a, fig. 202) ; the incus, or anvil (b) ; the os orbicu- 

 lare, a minute globular bone (c); and the stapes, or stirrup- 

 bone (d). These bones are connected together in the manner 

 represented in fig. 203 ; where a a represents the wall of the 

 tympanic cavity ; 5, the membrana tympani ; c, one of the 

 long processes of the malleus, which is attached to the mem- 

 brane ; d, the head of the malleus, which articulates with the 

 incus ; e, the other long process of the malleus, which is 

 acted-on by the minute muscle f, that serves to tighten the 

 tympanum ; g, the incus, of which one leg is in contact with 

 the wall of the cavity, whilst the other is connected with the 

 orbicular bone h ; i, the stapes, of which the upper end is 

 connected with the orbicular bone, whilst the lower (which is 

 of an oval form) is attached to the membrane that covers the 

 entrance to the internal ear ; and Tc is a small muscle which 



