THE ANATOMY OF BIRDS.— NEUBOLOGY. 
189 
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stapes were uustepped (in life, of course, both these ''windows" are closed by membranous 
curtains). Now in birds the cochlear cavity and its bony or cartilaginous contents are only the 
beginnings of such structure — a strap-shaped or tongue-like protrusion from the vestibule, as 
if a part of the first mammalian whorl, and very incompletely divided into scala vestibuli and 
scala tympani by a 
gristly structure (rep- 
resenting the modi- 
olus and its lamina), 
which proceeds from 
the bony bar or bridge 
between fenestra ova- 
lis and fenestra ro- 
tunda. (See figs. 84, 
85.) This structure 
is the most intimate 
and essential part of 
the organ of hearing, 
for upon it spread the 
terminal filaments of 
the auditory nerve. 
A human or any 
well-developed mam- 
malian cochlea is a 
thing of marvellous 
beauty, even as to 
its bony shell — there 
is nothing to com- 
pare with its exqui- 
site symmetry ; while 
the spiral radiation 
of the nervous tissue 
introduces yet other 
and more wondrous 
'' curves of beauty." 
The vestibule hard- 
ly requires special de- 
scription; it is simply 
the central chamber 
common to the coch- 
lear and canalicular 
cavities ; receiving 
the mouth of the 
scala vestibuli of the 
cochlea; the several 
mouths of the separate or uniting semicircular canals ; opening into tympanum by fenestra ova- 
lis ; conducting to meatus auditorius internus by the course of the auditory nerve. In the 
eagle, if its irregularities of contour were smoothed out, it would about hold a pea. 
In the language of human anatomy, the three semicircular canals are the (a) anterior or 
superior vertical, the (6) posterior or inferior vertical, and the (c) external or horizontal ; and 
the planes of their respective loops are approximately mutually perpendicular, in the three 
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