THE NERVOUS SYSTEM. 225 
of the stapes is attached. The ventral one is the fenestra 
rotundum, also closed by a membrane in the recent state. 
In the dry skull the fenestra ovalis opens into the first or 
basal whorl of the cochlea, and the fenestra rotundum opens 
into the vestibule of the internal ear. The Eustachian tube 
(Fig. 18), whose opening may be seen craniad of the audi- 
tory bulla, connects the middle ear with the posterior nares 
and thus admits air to the tympanic cavity. 
To demonstrate further the anatomy of the middle ear, 
one should clean the flesh from a 
fresh or preserved head and care- 
fully cut away the ventral walls 
of both chambers of the auditory 
bulla (Fig. 17). 
In the middle ear are three 
bones, the malleus, incus, and 
stapes, commionly called hamimer, a6 o77- Diced op cue 
anvil, and stirrup. They form a Mammalian Ear. 
. : The internal ear is repre- 
crooked chain across the cavity. sented removed about a 
The long process of the malleus is ence niet ie mid- 
: e ear and slightly ro- 
fastened throughout nearly its tated to the left. The 
whole length to the inner surface base of the stapes, s, in 
: : nature, covers the fenes- 
of the membrana tympani, and its tra ovalis, ov; c, basal 
‘ Fi whorl of the cochlea; ea, 
enlarged extremity articulates external auditory meatus; 
with the body of the incus. The spree of the Eu- 
stachian tube; 7, incus; in, 
latter has two legs, to one of malleus; sc, semicircular 
which the stapes is attached. The canals; ve, vestibule; t, 
tympanum. 
base of the stapes is inserted in 
the membrane closing the fenestra ovalis (Figs. 17 and 
III). 
The internal ear, or labyrinth, consists of three parts— 
the vestibule, cochlea, and semicircular canals (Figs. 18 
and 111). All of these parts are of membrane and lie in 
cavities of corresponding shape within the petrous bone. 
