370 ELEMENTARY PHYSIOLOGY less. 



tube (Eu. Figs. 118 and 110), which leads directly from 

 the fore part of the drum inwards to the roof of the 

 pharynx, where it opens. (See also Fig. 69.) 



Two other orifices exist in the bony wall of the middle 

 ear, they are called the fenestra omdu (Fig. 119, F.o.) and 

 the fenestra rotunda (F.r.) respectively. Through these 

 the middle and inner ears would communicate with one 

 another were not a membrane stretched across each. 

 (See p. 375.) 



(iii) The Auditory Ossicles. — Three small bones, the 

 auditory ossicles, lie in the cavity of the tympanum. One 

 of these is the stapes, a small bone shaped like a stirrup. 

 The foot-plate of this bone is firmly fastened to the mem- 

 brane of the fenestra ovalis, while its hoop projects 

 outwards into the tympanic cavity (Figs. 119 and 122). 



Another of these bones is the malleus {Mall. Figs. 

 118, 119, 122), or hammer-bone, a long process, the so- 

 called handle, oi which is fastened to the inner side of the 

 tympanic membrane (Fig. 122); while a very much smaller 

 process, the slender process, is fastened, as is also the body 

 of the malleus, to the bony wall f)f the tympanum by 

 ligaments. The rounded surface of the head of the 

 malleus fits into a corresponding hollowed surface in the 

 end of a third bone, the incus or anvil bone, thus 

 forming a joint of a somewhat peculiar character. The 

 incus has two processes ; of these one, the shorter, is 

 horizontal, and rests u[)on a support afforded to it by the 

 walls of the tympanum ; while the other, the longer, is 

 vertical, descends almost parallel with the long process of 

 the malleus, and articulates ' with the stapes (Figs. 119 

 and 122). 



The three bones thus form a movable chain between 

 the fenestra ovalis and the tympanic membrane. The 

 malleus and incus are, by the peculiar joint spoken of 



1 A minute bone, the os orbiculare, intervenes between the end of the 

 process of the incus and the stapes, so that the stapes is in reality articu- 

 lated with the OS orbiculare, wliich in turn is f.istcned to the process of 

 the incus. For simplicity's sake, mention of this is omitted above. 



