. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. AUDITORY ORGANS. I87 and may have to do with the recognition of sound waves of different rapidity. It has recently been shown that the membrana tectoria is connected with -the hairs of the hair cells. The fact that in birds, where pitch is certainly recognized, there is no organ of Corti, renders all speculation doubtful. he. FIG. 187.—Organ of Corti of guinea pig, after Schneider, d, Deiter's cells; he, Henson's cells; ih, inner hair cells; ip, inner pillar cells; Is, limbus spiralis; mt, membrana tectoria; n,
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. AUDITORY ORGANS. I87 and may have to do with the recognition of sound waves of different rapidity. It has recently been shown that the membrana tectoria is connected with -the hairs of the hair cells. The fact that in birds, where pitch is certainly recognized, there is no organ of Corti, renders all speculation doubtful. he. FIG. 187.—Organ of Corti of guinea pig, after Schneider, d, Deiter's cells; he, Henson's cells; ih, inner hair cells; ip, inner pillar cells; Is, limbus spiralis; mt, membrana tectoria; n, nerve fibres; oh, outer hair cells; op, outer pillar cells; si, inner sulcus; st, scala tympani; t, tunnel; In, tunnel nerve. The Middle Ear or tympanum first appears in the anura. It con- sists of a cavity (cavum tympani) in front of and below the otic capsule, connected by a slender duct, the Eustachian tube, with the pharynx. Externally it is separated from the outer world by a thin partition, the tympanic membrane, from which a chain of bones, the ossicula auditus (p. 73), extends across the cavity to the fenestra ovale, and serves to transmit the sound waves to the inner ear. The tympanic cavity is the homologue of the spiracular cleft of the elasmobranchs (see respiration), which never breaks through. The tympanic mem- brane, covered externally with ectoderm, on the inner surface with entoderm, represents the imperforate wall of the cleft, while the Eusta- chian tube is the narrowed internal end of the spiracle. The chain of ear bones has already been described. It is to be noted that the chain consists of columella and stapes in anura and sauropsida, while in the mammals columella is replaced by incus and malleus. In the urodeles and gymnophiones, where no tympanic cavity is devel- oped, the quadrate articulates with the stapes. The External Ear.—In the anura and in many reptiles the tym- panic membrane is flush with the surface of the head, but in other rep- tiles
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1912
