THE ANATOMY OF BIRDS. — NEUROLOGY. 185 
especially in fig. 71, where the stapes, st, is seen lying in the ear-cavity, the tympanum having 
been removed. 
There is ordinarily no external ear, in the sense of a fleshy conch or auricle, though owls 
at least have a considerable flap which overlies the auditory aperture. The place of an auricle 
is filled by a set of peculiarly modified feathers surrounding and overlying the opening, called 
in ornithology the ear-coverts, or auriculars (p. 97; fig. 25, 96). The outer ear or meatus 
auditorius externus is a considerable shallow roundish depression in the skull, at the extreme 
lower lateral corner. Its ordinary boundaries are the movably articulated quadrate bone in 
front, the expanded rim of the squamosal above, the tympanic wing of the exoccipital behind 
and below; the termination of the basitemporal also usually contributing to the under boundary. 
(See fig. 71, at st; 63, underl; fig. 62, where reference lines ‘‘ bones of ear cell” go.) On 
removing the quadrate from the dry skull, the general tympanic depression is seen to be more 
or less continuous with the alisphenoid ; the boundary is best marked behind and below by the 
broad thin sharp-edged shell of the tympanic wing of the exoccipital. To the brim indi- 
cated is attached the tympanum, or drum of the ear —that membrane being, from the con- 
figuration of the parts, quite superficial, — not at the bottom of a tube-like meatus, as in man. 
The membrane proper is invested externally by modified common integument which readily 
peels off. Thus this wide shallow depression overlaid with feathers or a slight flap is all there 
is to represent the ‘‘ outer ear-passage.” The tympanic membrane sometimes develops slight 
ossification, which then represents the ‘‘ tympanic bone,” or ‘‘ external auditory process ” of 
human anatomy. Did not this membrane occlude the way, the passage through the ear to the 
mouth would be pervious. This passage is the modified persistence of the first visceral cleft or 
‘« gill-slit” of the embryo. Just within the tympanic membrane is the cavity of the tympanum 
or middle ear, which may be very extensively exposed by merely removing the membrane. 
Looking into this cavity, as may readily be done from the outside, in carefully cleaned dry 
skulls, many objects of interest are presented; among them, a number of foramina — openings 
leading in various directions. In the first place there are some (inconstant and not readily 
identified) holes, which are pnewmatic openings, conveying air from the middle ear-passage to 
the interior of bones of the skull and lower jaw. Next is observed a large oritice in the lower 
anterior part of the cavity, —the mouth of the eustachian tube. This tube continues the ear- 
passage to the mouth ; opening at the back of the hard palate by a median orifice in common 
with its fellow. In clean skulls of any size a bristle, or even a wooden tooth-pick, will pass 
through the eustachian tube, and appear upon the floor of the skull in mid-line or nearly there, 
under the basisphenoid, over the basitemporal. The foregoing passages have not conducted 
us to the immer ear or proper acoustic cavity. There will be observed, in the side-wall of the 
tympanic cavity, two definite openings near the eustachian orifice. One of these, anterior and 
superior to the other, larger usually, and oval, is the fenestra ovalis; it lies in the obliterated 
suture between the prodtie and opisthotic bones; and when the membranous curtain which 
closes it in life is gone, you look through this ‘‘ oval window ” into the vestibular cavity of the 
ear proper. The lower, posterior, circular orifice is the fenestra rotunda; through which round 
window in the opisthotic bone you look into the cochlear cavity of the ear proper. Fenestra 
ovalis and f. rotunda are generally close together, — only divided by a little bridge of bone, or a 
mere bony bar. To the circumference of the fenestra ovalis is fitted the expanded oval foot of 
the trumpet-shaped columella auris, — the stapes, or “ stirrup-bone,” as it is called in mammals 
(fig. 83, st). This is an elegant little bone, which establishes mechanical connection between 
the membrane closing the fenestra ovalis and the tympanic membrane, — something on the 
principle of the ‘‘ sounding-post” inside a violin. It is shown magnified greatly in its embry- 
onic condition, in fig. 67, and there seems to be primitively and morphologically the proximal 
connection of the hyoid bone (by cerato-hyal elements) with the bony capsule of the ear; but 
no trace of this relation persists. Fig. 83 shows the mature stapes of a fowl, and indicates its 
