. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 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. \ -Con1 Ma* Mt. FIG. 167.—DIAGRAM OF THE ENTIRE AUDITOR
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 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. \ -Con1 Ma* Mt. FIG. 167.—DIAGRAM OF THE ENTIRE AUDITORY ORGAN OF MAX. External Ear.—M, M, pinna ; Mae, external auditory meatus ; 0, wall of latter ; Mt, tympanic membrane. Middle Ear.—Ct, Ct, tympanic cavity ; Ol, wall of same; S'Ap, 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 ; Tbl, its opening into the pharynx ; 0", its wall. Internal Ear, with the greater part of the bony labyrinth (KL, KL1) removed.— S, sacculus ; a, b, the two vertical canals, one of which (b) is shown cut through ; c, Co, commissure of the'canals of the membranous and bony labyrinths re- spectively ; , , saccus and ductus eudolymphaticus ; the latter bifur- cates at 2 ; Cp, cavum perilymphatieum ; Or, caualis reuniens ; Con, mem- branous cochlea, which gives rise to a blind sac at + ; Con1, bony cochlea ; Sv and St, scala vestibuli and scala tympani, which at * pass into one another at the cupula terminalis (Cl) ; , ductus perilymphaticus, which arises from the scala tympani at d, and opens at 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 lam
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