164 
MR. TOYNBEE ON THE STRUCTURE OF 
latter bone is so suspended by means of the processus gracilis and the short process 
of the incus*, that the long process can move inwards towards the tympanic cavity, 
and outwards towards the meatus (fig. 14). It must be evident, therefore, that in 
order to prevent the concave membrana tympani, with the above attachments, from re- 
maining in a state of relaxation, either the tensor tympani muscle must be in a state of 
continual contraction, or some other provision must exist for retaining the membrana 
tympani in the moderately tense condition fitting it to receive the sonorous undula- 
tions. The provision which actually exists, and which, so far as I am aware, has 
hitherto escaped the attention of anatomists, is the tensor ligament of the membrana 
tympani. 
The ligament in question is about three-fourths of a line in length, and it is 
attached internally to the cochleariform process, and externally to that part of the 
inner surface of the malleus where the long process joins the neck (fig. 15). In the 
interior of this ligament, which presents a tubular shape, is placed the tendon of the 
tensor tympani muscle. It is thin anteriorly, where it consists of very delicate 
fibres, but the remainder is thick and dense, being composed of firm ligamentous 
tissue. So long as this ligament remains entire and the membrana tympani un- 
injured, the latter structure retains its natural degree of concavity and tenseness; 
but upon the ligament being cut through, or upon a solution of continuity being 
efifected as the result of disease, the membrana tympani becomes very flaccid, even 
though the tendon of the tensor tympani muscle remains entire. In a preparation, 
when the tensor tympani muscle is pulled -I-, the membrana tympani is rendered very 
tense, and the tensor tympani ligament is relaxed ; but immediately that the muscle 
is relaxed the membrana tympani is observed to return to its usual state, and the 
ligament is again rendered tense. 
On the Functions of the Fibrous Lamince of the Membrana Tympani. 
It is obvious that one use of the fibrous laminae of the membrana tympani is to 
present a firm but delicate membranous septum for the reception of sonorous undu- 
lations. The arrangement of the two sets of fibi'es at right angles to each other has 
* The short process of the incus is attached to the margin of the mastoid cells by ligamentous fibres, which 
allow of a lateral motion only. 
t The tensor tympani muscle has an attachment which appears not to have been hitherto noticed. The 
tendon is generally described as passing backwards from the muscle, and then turning outwards over the 
cochleariform process to be attached to the malleus ; but previously to changing its direction this tendon is 
very firmly attached by strong ligamentous tissue to the posterior extremity of the groove of the tensor tym- 
pani muscle (fig. 16). When the muscle contracts, these ligamentous fibres are put on the stretch, and the 
portion of the tendon that passes to the malleus being also stretched, the malleus is drawn in, and the mem- 
brana tympani rendered tense ; but with whatever degree of force the muscle may afterwards be pulled, the 
membrana tympani itself is not rendered more tense in the slightest degree, the whole strain being on the 
above-described ligamentous fibres attached to the groove. If these fibres are cut through and the muscle be 
tightly drawn, the membrana tympani is ruptured. 
