Henry Gray (1825–1861). Anatomy of the Human Body. 1918.
pages 1300
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FIG. 1206– The interior of the posterior half of the left eyeball. (See enlarged image) |
The Ear.—The various prominences and fossæ of the auricula (see page 1034) are visible (Fig. 1207). The opening of the external acoustic meatus is exposed by drawing the tragus forward; at the orifice are a few short crisp hairs which serve to prevent the entrance of dust or of small insects; beyond this the secretion of the ceruminous glands serves to catch any small particles which may find their way into the meatus. The interior of the meatus can be examined through a speculum. At the line of junction of its bony and cartilaginous portions an obtuse angle is formed which projects into the antero-inferior wall and produces a narrowing of the lumen in this situation. The cartilaginous part, however, is connected to the bony part by fibrous tissue which renders the outer part of the meatus very movable, and therefore by drawing the auricula upward, backward, and slightly outward, the canal is rendered almost straight. In children the meatus is very short, and this should be remembered in introducing the speculum. |
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FIG. 1207– The auricula or pinna. Lateral surface. (See enlarged image) |
| Through the speculum the greater part of the tympanic membrane (Fig. 1208) is visible. It is a pearlygray membrane slightly glistening in the adult, placed obliquely so as to form with the floor of the meatus an angle of about 55°. At birth it is more horizontal and situated in almost the same plane as the base of the skull. The membrane is concave outward, and the point of deepest concavity—the umbo—is slightly below the center. Running upward and slightly forward from the umbo is a reddish-yellow streak produced by the manubrium of the malleus. This streak ends above just below the roof of the meatus at a small white rounded prominence which is caused by the lateral process of the malleus projecting against the membrane. The anterior and posterior malleolar folds extend from the prominence to the circumference of the membrane and enclose the pars flaccida. Behind the streak caused by the manubrium of the malleus a second streak, shorter and very faint, can be distinguished; this is the long crus |