Membrane Tympani (drum) which separates the external ear from the tympanic cavity.  To examine the drum, you must pull the ear backward and outward to make the canal straight.

Membrane Tympani (the drum) Membrane.—­This is situated at the inner end of the canal and separates it from the tympanum or middle ear.  It is placed like the membrane in the telephone.  It is pearly gray in color.  This membrane not only serves as a protection to the delicate structures within the tympanum, but also receives the sound vibrations from without and transmits them to the ossicular (bony) chain of the middle ear.

The Tympanum or Middle Ear.—­This cavity just beyond the drum, which forms the greater part of its outer wall, is an irregular cavity, compressed from without inward and situated in the petrous bone.  The mastoid cells lie behind.  It is filled with air and communicates with the nose-pharynx (naso-pharynx) by the eustachian tube.  The upper portion of this cavity, the attic, lies immediately below the middle lobe of the brain, separated from it by a thin layer of bone, which forms the roof of the cavity.  This cavity is separated from the internal ear.

[Eye and ear 359]

The Eustachian tube.—­This is the channel through which the middle ear communicates with the pharynx.  With an opening in the anterior of the middle ear, a bony canal passes from this point, inward, forward, and downward through the petrous bone, when it merges into a cartilaginous canal, which terminates in a funnel-shaped protuberance, with a slit-like orifice, located in the nose pharynx.  This is the eustachian tube.  It is lined with mucous membrane like the throat.  The air goes up from the throat, through this canal to the middle ear.  The mucous membrane of the middle ear is continuous with that of the nose-pharynx through the eustachian tube.  So you can readily understand how easy it is for an inflammation of the throat to extend to the middle ear through the eustachian tube.

The posterior wall which has the greatest height, reveals in its upper portion a passage (antrum) through which the vault of the tympanum (attic) communicates with the cells of the mastoid process, situated posteriorly.  From this description you see how near to each other these parts are placed and when one becomes diseased the disease can extend to the other part or parts.  The brain is separated from some of these cavities by a very thin shell of bone, and the disease can soon affect the brain through infection or breaking through the thin structures that separates the parts.

Diseases of the middle ear and the mastoid are always to be considered serious, and should be very closely watched.  A child with a running ear is in danger, for it may at any time become closed up and serious.

Eczema of the external ear (Auricle).—­This is an inflammatory disease of the skin, and in the poorer classes it is very frequent.  It is quite a common disease in old age.  It develops in other parts of the body at the same time in a certain percentage of cases.