Tympanic Membrane Anatomy

It forms the partition between the external acoustic canal
and the middle ear. It is obliquely set and as a result, its posterosuperior
part is more lateral than its antero-inferior
part. It is 9-10mm tall, 8-9 mm wide and 0.1 mm thick.
Tympanic membrane can be divided into two parts:
(a) Pars Tensa
It forms most of tympanic membrane. Its periphery is
thickened to form a fibrocartilaginous ring called the
annulus tympanicus which fits in the tympanic sulcus. The
central part of pars tensa is tented inwards at the level of
the tip of malleus and is called the umbo. A bright cone
of light can be seen radiating from the tip of malleus to
the periphery in the anteroinferior quadrant (Fig. 1.2).
(b) Pars Flaccida (Shrapnel's Membrane)
This is situated above the lateral process of malleus between
the notch ofRivinus and the anterior and posterior
malleal folds (earlier called the malleolar folds). It is not
so taut and may appear slightly pinkish. Various landmarks
seen on the lateral surface of tympanic membrane
are shown in Fig. 1.2.
Layers of Tympanic Membrane
Tympanic membrane consists of three layers:
(i) Outer epithelial layer, which is continuous with
the skin lining the meatus.

(ii) Inner mucosal layer, which is continuous with the
mucosa of the middle ear.

(iii) Middle fibrous laye r, which encloses the handle of
malleus and has three types of fibres-the radial,
circular and the parabolic.
Fibrous layer in the para flacc ida is thin and not organised
into various fibres as in pars tensa.

Nerve Supply:

(i) Anterior half of lateral surface: auriculotemporal
(V 3)'
(il) Posterior half of lateral surface: auricular branch of
vagus (CN X):
(iii) Medial surface: Tympanic branch of CN IX
(Jacobson's nerve).