AUDITORY ORGAN. 



203 



appears to be cut out of the substance of the periotic capsule, is 

 taken by some observers (Kolliker, Moldenhauer) to prove that it 

 has not a visceral origin, but this fusion is probably a secondary 

 condition (cp. columella of Amphibia, p. 198). In Monotremes, 

 several Marsupials, and some Edentates, the stapes is imperforate 

 and columelliform ; in all other Mammals it is stirrup-shaped, and 

 encloses the stapedial artery. 



/ 



FIG. 167. DIAGRAM OF THE ENTIRE AUDITORY ORGAN OF MAX. 



External Ear. M, M, pinna ; Mae, external auditory ineatus ; 0, wall of latter ; 

 Mt, tympanic membrane. 



Middle Ear. Ct, Ct, tympanic cavity; O l , wall of same; SAp, sound-conducting 

 apparatus, drawn in the form of a rod, representing the auditory ossicles ; 

 the point t corresponds to the stapes which closes up the fenestra ovalis ; M, 

 fenestra rotunda ; Tb, Eustachian tube ; Tb l , its opening into the pharynx ; 0", 

 its wall. 



Internal Ear, with the greater part of the bony labyrinth (KL, KL 1 } removed. 

 S, sacculus ; a, b, the two vertical canals, one of which (b) is shown cut through ; 

 c, Cffj commissure of the canals of the membranous and bony labyrinths re- 

 spectively ; S.e, D.e, saccus and ductus endolymphaticus ; ^ the latter bifur- 

 cates at 2 ; Cp, cavum perilymphaticum ; Cr, canalis reuniens ; Con, mem- 

 branous cochlea, which gives rise to a blind sac at + ; Con 1 , bony cochlea ; Sv 

 and St, scala vestibuli and scala tympani, which at * pass into one another 

 at the cupula terminalis (Ct) ; D.p, ductus perilymphaticus, which arises from 

 the scala tympani at d, and opens at D.p 1 . The horizontal canal is seen 

 between 2 and S. 



To understand the auditory organ, and more particularly the 

 membranous cochlea, of Mammals, it is necessary to examine the 

 bony cochlea. The axis of the latter lessens in size from base 

 to apex (Fig. 168, A) and round it a bony lamella (lamina spiralis 

 ossea) winds in a spiral manner ; this extends into the cavity of 

 the coils of the cochlea without quite reaching as far as the 



