THE ANATOMY OF BIRDS.— NEUHOLOGT. 



189 



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stapes were unstepped (in life, of course, botli 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 

 tlie 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 



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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 vestibulehaTd- H 

 ly requires special de- » 

 scription; it is simply ^ 

 the central chamber ^ 

 common to the coeh- "' 

 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 ; aud 

 the planes of their respective loops are approximately mutually perpendicular, in the three 



