. Comparative anatomy. Anatomy, Comparative. THE SENSE ORGANS 599 the meatus, is the concha. The opening of the meatus is guarded by two processes, a ventral tragus next the cheek and a dorsal antitragus opposite. The incurved outer rim of the auricle is the helix. The antihelix is a smaller ridge which bounds the concha dorsally. The walls of the meatus are supported laterally by fibro-cartilage and medially by bone and lined by skin. The meatus is beset with hairs, and contains many tubular glands, which secrete the ear-wax. The Middle Ear. A tympanic membrane or ear-drum separates the exter
. Comparative anatomy. Anatomy, Comparative. THE SENSE ORGANS 599 the meatus, is the concha. The opening of the meatus is guarded by two processes, a ventral tragus next the cheek and a dorsal antitragus opposite. The incurved outer rim of the auricle is the helix. The antihelix is a smaller ridge which bounds the concha dorsally. The walls of the meatus are supported laterally by fibro-cartilage and medially by bone and lined by skin. The meatus is beset with hairs, and contains many tubular glands, which secrete the ear-wax. The Middle Ear. A tympanic membrane or ear-drum separates the external meatus from the tympanic cavity or middle ear, within which lie the ear bones. Leading from the tympanic cavity to the pharynx, is the auditory or Eustachian tube, which serves to equalize the atmospheric. -COCHLEAR NERVE "~"'~^''i#j55*^-COCHLEAR DUCT EUSTACHIAN TUBE Fig. 496.—The human ear. "Sound waves" impinge upon the drum and are carried by the three ear bones to the fenestra vestibuli and thus to the scala vestibuli and the cochlear duct. (Redrawn from W. H. Howell after Czermak.) pressure on the two sides of the tympanic membrane, so that this may vibrate freely. Temporary deafness occurs when the auditory tube is closed because of inflammation caused by a cold. Functionally, however, the most important elements of the middle ear are the three ear bones. The Internal Ear. The membranous sac or true organ of equilibration and hearing is so complex that it is frequently called the membranous labyrinth. The otic bone in which it is embedded takes on its shape and is equally complex, and hence is known as the bony labyrinth. Except in the region where the membranous labyrinth is attached to the bone, it is surrounded by a cavity iilled with the perilymph. The sac itself is filled with endolymph. (Fig. 495) The Organ of Equilibration. The function of equilibration in man is served, as in lower vertebrates, by the utriculus and the three semicircular
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