THE ANATOMY OF BIRDS. —NEUROLOGY. 185 



especially in fig. 71, where the stapes, st, is seen lyiug in the ear-cavity, the tympanum having 

 been removed. 



There is ordinarily no external ear, in the sense of a fleshy couch 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 ; tig. 25, 36). The outer ear or meatus 

 oiiditorius externus is a considerable shallow roundish depression in the skull, at the extreme 

 lower lateral comer. 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, under?; 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 readUy 

 peels oflF. 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 vpithin 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 pneumatic openings, conveying air from the middle ear-passage to 

 the interior of bones of the skull and lower jaw. Next is observed a large orifice 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 inner ear or proper acoustic cavity. There will be observed, in the side-wall of tlie 

 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 prootic 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 hjwer, 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 ovahs 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 



