406 TYMPANIC CAVITY AND CHAIN OF BONES. 
of the nasal cavity (n, fig. 200) by a canal termed the Eusta¬ 
chian tube (7c, 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 
9 d 
a b 
l 
i 
d 
Fig. 202. —Bones oe 
the Ear. 
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; b, 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 j and 7c is a small muscle which 
