406 TYMPANIC CAVITY AND CHAIN OF BONES. 
of the nasal cavity (n, fig. 200) by a canal termed the Eusta-— 
chian tube (A, 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 
Ve 
Fig. 202.—BonrEs oF Fig. 203.—Caviry oF THE TYMPANUM, WITH 
THE Ear. THE BoNES IN THEIR PLACES, 
hammer (a, fig. 202) ; the incus, or anvil (6); the os orbieu- 
lare, a minute globular bone (c); and the stapes, or stirrup- 7 
bone (d). These bones are connected together in the manner 7) 
represented in fig. 203 ; where a a represents the wall of the 
tympanic cavity; }, the membrana tympani; ¢, 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 ; ¢, 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 & is a small muscle which ie 
