The Organs of Hearing.
The External Ear is composed of the pavilion of the ear (the pinna), and
the auditory canal (the meatus auditorius externus). The Pinna surrounds
the entrance to the auditory canal. It stands out from the head, and is
in common language called the ear. The Meatus Auditorius in a canal
about an inch long, partly bony and partly cartilaginous, which goes
from the pavilion of the ear to the drum of the ear. The Drum of the Ear
(membrana tympani) is an ovalshaped thin membrane, inserted into a
groove around the auditory canal.
The Tympanum is a cavity within the temporal bone.
The Eustachian Tube is a channel of communication between the tympanum and the upper part of the pharynx. The object of this is to convey air to the drum of the ear, as without air no sound can be produced. The Labyrinth is a series of chambers through the petrous bone embracing the vestibule, a three cornered cavity within the tympanum; the semieircular canals, communicating with the vestibule, and the cochlea,which makes two and a half turns around an axis, called the modiolus. In Fig. 58, a, is the pavilion of the ear; e, the auditory canal; g, the membrana tympani; k, the tympanum ; e, the bones of the ear; b, the semicircular canals the cochlea; 7t, the vestibule ; i, the eustaebian tube; d, the auditory nerve. In Fig. 59, we have a view of the labyrinth laid open, and highly magnified: 1, 1, being the cochlea; 2, 3, the channels that wind around the central point (5); 7, 7, the vestibule; 8,the ioramen rotundum; 9,the fenestra ovalis; 4, 6, 10, the semicircular canals.
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