EA R—EA S TERLING 



i8i 



The position of these parts is shewn in the adjoining figure. 

 The basal portion of the membranous cochlea, the " ductus coch- 

 learis," communicates with the sacculus by a canal, the dorsal wall 

 of which is continued into the 



Per. 



tegmentum 



vasculosum or 

 membrane of Reissner, Avhile 

 the ventral wall contains the 

 basilar membrane, with its 

 acoustic papilla or organ of 

 Corti. The space between the 

 periosteum of the bony wall of 

 the cochlea and the tegmentum 

 is called " scala vestibuli " ; 

 that between the bone and the 

 basilar membrane is the " scala 

 tympani." 



The scalfe are part of the 

 perilymphatic space between 

 the membranous and the bony 

 inner ear, and are filled with 



Vertical Median Section of the Cochlea 

 OF A Pigeon, magnified 30'times. (After Retzius.) 



B.g. Blood-vessels ; G. Ganglia in the ramus 

 basilaris of the cochlear portion of the acoustic 

 nerve ; E.S. JV.5. Cartilaginous frame of the cochlea; 

 M.h. Merabrana basilaris ; M.t. Membrana tectoria ; 

 F.a.b. Papilla acustica basilaris ; Per. Periost of 

 the cochlea; Sc.V. Scala vestibuli; Set. Scala 

 tympani ; T.v. Tegmentum vasculosum. 



the perilymphatic fluid. 



The acoustic nerve enters the membranous ear near the base of 

 the cochlea, and terminates by eight maculae, jDapillae, and crista? 

 acusticte in the ampulhe and various other dilatations. The cells of 

 these terminating nervous spots are cylindrical, and end in one or 

 more extremely fine filaments or hairs ; they extend into the 

 endolymphatic fluid, which fills the whole membranous ear, and 

 contains, especially in the sacculus, numerous small otolithic crystals 

 of carbonate of lime. The filamentous and hairy cells take up the 

 vibrations or waves of sound which are transmitted from the 

 typanum through the columella to the endolymphatic fluid, and 

 convey them through the acoustic nerve to the brain. 



The whole inner ear is subject to comparatively few and unim- 

 portant variations, and does not throw much light upon the 

 afltinities of the various groups of Birds, the differences being 

 restricted chiefly to the relative size of the cochlea and the position 

 and size of the semicircular canals. It cannot be doubted that the 

 faculty of hearing is highly developed in Birds, not only the mere 

 perception of sound, but also the power of distinguishing or under- 

 standing pitch, notes and melodies, or music. 



For further infoi'mation concerning the minute structure of the 

 ear, see the monumental work of G. Retzius (Das Geh'Ororgan der 

 WirheltUere, Stockholm: 1884, ii. pp. 139-198, pis. 15-20). 



EASTERLING, according to Latham, a local name for the 



WiGEON. 



