THE ANATOMY OF BIFDS. — NEUROLOGY. 



189 



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 |^g.^p.,-._.^2:»-5r--^-'-== 

 gristly structure (rep- |s| ||| t£fo §11 '? ^^ 



resenting the modi- •^S^|3|ii^3otlis|i!£-S_. „ 

 olus and its lamina), £5g,|»c=-, ■^a^l-^i.s^lo- ^- 

 which proceeds from S-^-gg^So-Sogcio 

 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- "f | I S ^ 

 site symmetry ; while E. |- ? " " 

 the spiral radiation | a 5 

 of the nervous tissue *- ^ S 

 introduces yet other r f | 

 and moi'e 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 



