The tympanic membrane forms the major part of the lateral wall of the middle ear (see ▶ Fig. 2.1, ▶ Fig. 2.2, ▶ Fig. 2.3). It is thin, resistant, semi-transparent, has a pearly gray color, and is cone-like. The apex of the membrane lies at the umbo, which corresponds to the lowest part of the handle of the malleus. Most of the membrane circumference is thickened to form a fibrocartilaginous ring, the tympanic annulus, which sits in a groove in the tympanic bone called the tympanic sulcus. The fibrocartilaginous ring is deficient superiorly. This deficiency is known as the notch of Rivinus. The anterior and posterior malleolar folds extend from the short process of the malleus to the tympanic sulcus, thus forming the inferior limit of the pars flaccida of Shrapnell’s membrane.
The membrane forms an obtuse angle with the posterior wall of the external auditory canal. It also forms an acute angle with the anterior wall of the canal. It is important to respect this acute angulation in the myringoplasty operation to maintain as much as possible the vibratory mechanism of the tympanic membrane and hence ensure maximum hearing improvement (see ▶ Fig. 2.4, ▶ Fig. 2.5, ▶ Fig. 2.6, ▶ Fig. 2.7, ▶ Fig. 2.8).
The external surface of the tympanic membrane is innervated by the auriculotemporal nerve and the auricular branch of the vagus nerve, whereas the inner surface is supplied by Jacobson’s nerve, a branch of the glossopharyngeal nerve.
The blood supply is derived from the deep auricular and anterior tympanic arteries. Both are branches of the maxillary artery.
Fig. 2.1 Right ear. Normal tympanic membrane. 1, pars flaccida; 2, short process of the malleus; 3, handle of the malleus; 4, umbo; 5, supratubal recess; 6, tubal orifice; 7, hypotympanic air cells; 8, stapedius tendon; c, chorda tympani; I, incus; P, promontory; o, oval window; R, round window; T, tensor tympani; A, annulus.
Fig. 2.2 Right ear. Structures of the middle ear seen after removal of the tympanic membrane. 9, pyramidal eminence; co, cochleariform process; f, facial nerve; j, incudostapedial joint. See legend to ▶ Fig. 2.1 for other numbers and abbreviations.