This is the tympanic membrane. It separates the external meatus from the middle ear, or tympanic cavity. The tympanic membrane is so thin that it's partly transparent. This small upper part of the tympanic membrane, the pars flaccida, is slack. This much larger part below, the pars tensa, is tense.
The tense part of the tympanic membrane has the shape of a shallow cone: it's drawn inwards by its attachment to the handle of the malleus, which we can just see here. The apex of the cone, where the tip of the malleus is attached, is called the umbo.
The tympanic membrane faces downwards and forwards. This is a true lateral view of it. When seen from the side, it's tilted in this plane. When sound waves strike it, the tense part of the tympanic membrane vibrates. Its vibration is transmitted to the malleus.
The tympanic membrane is formed of a layer of skin on the outside and a layer of mucous membrane on the inside, lying back-to-back on a layer of supporting fibers.
The support fibers within the tympanic membrane are attached around the circumference, except between these two points, to a ring of fibrocartilage, the anulus. The anulus fits into a groove in the bone.
To see beyond the tympanic membrane we'll remove this part of the bone, leaving the anulus intact.
This brings us into the lower part of the tympanic cavity, or middle ear. We'll see a little more of it by dividing the tympanic membrane along this line, and removing it. Here's the handle, or manubrium, of the malleus, attached to the tympanic membrane. Here below it we can see how thin the membrane is. Now we'll remove the rest of the tympanic membrane.