MIDDLE HAR OR TYMPANIC CAVITY. 707 
near the circumference, but scattered and few in number near the centre of 
the membrane (Fig. 516). Both radial and circular fibres are absent from the pars 
flaccida, which is constituted merely by the apposition of the cutaneous and mucous 
layers. Gruber pointed out that, in addition to the radial and circular fibres, there 
exists a series of dendritic or branched fibres, which are best developed in the 
posterior part of the membrane. 
The internal layer (stratum mucosum) is continuous with the general mucous 
lining of the tympanum. It is thicker over the upper part of the membrane than 
near its centre and is covered by pavement epithelium. 
Otoscopic Examination of the Tympanic Membrane (lig. 517).—The membrane, in the 
living, is of a “ pearl-gray ” colour, but may present a reddish or yellow ish tinge, depe nding upon 
the condition of its mucous hning oa on the eondition of the cutaneous hning of the me: atus - the 
posterior segment is usually clearer 
than the anterior. At the antero- 
superior part, close to its periphery, 
a whitish point appears as if pro- 
jecting towards the meatus; this rane Manta 
c . : 2 Z Anterior tympano- 
is the short process of the malleus. ‘nalleolar fold 
Passing downwards and backwards 
from this pomt to the umbo is a 
ridge caused by the handle of the Handle of malleus. 
malleus, the lower extremity of — Antero-superior _ 
which appears rounded. Two quadrant 
ridges, corresponding with the 
tympano - malleolar folds, extend 
from the short process of the 
malleus, one forwards and upwards, 
the other backwards and upwards. Fra. 517.—Lerr TyMPaNtIc MeMBRANE (as viewed 
Behind, and near the lower ex- auditory meatus). x 3. 
tremity of the handle of the 
malleus, is a reddish or yellowish spot, due to the promontory of the inner tympanic wall 
shining through. If the membrane be very transparent, the long process of the incus may 
be visible behind the upper part of the handle of the malleus, and reaching downwards 
as far as its middle. From the lower end of the handle of the malleus, the “cone of light” 
or “luminous triangle” extends downwards and forwards, its apex being "directed towards the 
handle; this triangle varies in size in different people. A line prolonging the handle down- 
wards divides the membrane into two parts, while another, drawn at right angles to this through 
the umbo, will subdivide it into four quadrants, viz. postero- superior, postero- infericr, antero- 
superior, and antero-inferior ; this subdivision is useful in enabling the otologist to localise and 
describe accurately the seat of lesions in the membrane. 
Vascular and Nervous Supply of the Membrana Tympani.—The arteries are arranged in 
two sets, one on the cutaneous and another on the mucous surface. These anastomose by means 
of small branches which pierce the membrane, especially near its periphery. The first set is 
chiefly derived from the deep auricular branch of the internal maxillary, whilst those on the 
mucous surface are small and proceed from the tympanic branch of the internal maxillary, and 
from the stylo-mastoid branch of the posterior auricular. The veins from the cutaneous surface 
open into the external jugular; those from the inner surface partly into the venous plexus on 
the Eustachian tube, and partly into the lateral sinus and veins of the dura mater. The outer 
surface of the membrane receives its nerves from the auriculo-temporal branch of the fifth and 
from the auricular branch of the vagus; the inner surface, from the nerve of Jacobson (tympanic 
branch of the glosso-pharyngeal). The "lymphatics, like the blood- vessels, are arranged in two 
sets, cutaneous and mucous, which, however, communicate freely with each other. ” Kessel has 
described as lymphatics the spaces between the branches of Gruber’s dendritic fibres. 
Posterior tympano- 
malleolar fold 
Short process of 
malleus 
Long process of 
incus 
Postero-superior 
quadrant 
Postero-inferior 
quadrant 
Cone of light 
Antero-inferior 
quadrant 
from the external 
The inner wall of the tympanic cavity (paries labyrinthica) is formed by the 
outer surface of the internal ear or labyrinth (Fig. 515). It presents—(1) a rounded 
eminence, the promontory (promontorium), which is caused by the first coil of the 
cochlea, and is grooved for the tympanic plexus of nerves. (2) An oval or some- 
what reniform opening, the fenestra ovalis seu vestibuli. This is situated above 
and behind the promontory, and its eo axis is directed from before backwards. 
It measures 3 mm. in length and 14 mm. from above downwards, and lies at the 
bottom of a AGRE shaped 1 recess, the fossula fenestre vestibuli. In the macerated 
bone it leads into the vestibule of the labyrinth, but is closed in the recent state 
by the foot of the stapes, surrounded by its ligamentum annulare. (35) An elevation, 
the prominentia canalis facialis. Situated above the fenestra ov he in the recessus 
epitympanicus, this indicates the position of the aqueduct of Fallopius, which con- 
tains the facial nerve and is continued backwards and downwards behind the 
