Relations.—Outer surface with the tragicus lateralis (4) and the fat about the concha. Inner surface with the concha.
Action.—Flexes the concha.
Strauss-Durckheim describes under the name cornetoconchæus a small muscle bridging the deep groove caused by the folding of the medial surface of the concha, its proximal end being close to the insertion of the abductor auris brevis ([page 100]). This muscle was absent in all of the cases examined for its presence.
M. conchæus externus ([Fig. 169], 9).—A quadrilateral muscle on the lateral surface of the concha. The cranial end of this muscle is attached to the concha a short distance distad of the antitragus along a dorsoventral line six to eight millimeters in length; the fibres pass thence caudodorsad a distance of about one centimeter, where they are again attached to the concha. The muscle thus bridges a shallow depression on the lateral surface of the concha.
Action.—Constricts the concha.
The Middle Ear.
Fig. 170.—Tympanic Membrane, Viewed from the Inner Side.
The outer wall of the bulla has been removed, carrying with it the tympanic membrane with the malleus and incus; these are now viewed from the side that was turned toward the cavity. a, bony ring forming inner end of external auditory meatus; b, b′, malleus; c, tympanic membrane; d, incus; e, lenticular process; f, chorda tympani nerve; g, cartilaginous support for chorda tympani nerve.
The middle ear is enclosed in a cavity within the tympanic bulla. Its outer boundary, as well as the inner boundary of the external ear, is formed by the tympanic membrane ([Fig. 170], c.) This is a thin, semitransparent membrane attached to the bony ring (a) surrounding the inner end of the external auditory meatus. It is oval in outline. Across the dorsal third of its inner surface runs the handle of the malleus (b), to which the membrane is firmly attached and which by pulling on the membrane gives it the form of a cone instead of a flat surface. The apex of the cone is directed mediad.