THE ANATOMY OF BIRDS.— NEUROLOGY. 



195 



stapes were unstepped (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- 



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2=2 a § » » » So 





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g 5^ 5 w " ir „ n. TO 



olus and its lamina i, 

 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 2 = s^ >3 



m O 1 ~. 



the organ of hearing, - ■"= ^ 

 for upon it spread the 

 terminal filaments of 

 the auditory nerve. 

 A human or any 

 well-developed mam- 

 malian cochlea 

 thing of marvellous 

 Iteauty, 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 I 

 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 tlie (c) external or horizontal ; and 

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



