160 
MR. TOYNBEE ON THE STRUCTURE OF 
In the Croonian Lecture, published in the nineteenth volume of the Philosophical 
Transactions, Sir Everard Home advanced the opinion that the mernbrana tympani 
in the human subject was muscular. His words are, “ When viewed in a microscope 
magnifying twenty-three times, the muscular fibres are beautifully conspicuous, and 
appear uniformly the same throughout the whole surface. There being no central 
tendon as in the diaphragm, the muscular fibres appear only to form the internal 
layer of the membrane, and are most distinctly seen when viewed on that side*.” The 
use of this radiated muscle. Sir Everard Home states, is to give those different degrees 
of tension to the membrane, which empower it to correspond with the variety of external 
tremors'!-.” Since the first publication of this opinion as to the muscularity of the 
mernbrana tympani, anatomists have generally conceded that it is fibrous, but they 
have widely differed as to its composition. According to Mr. Quain and Dr. Sharpey, 
“ it is made up of fine closely arranged fibres, the greater number of which radiate 
from near the centre to the circumference; but within these are circular fibres which 
are more scattered and indistinct, except close to the margin of the membrane, where 
they form a dense, almost cartilaginous ring;|:.” Mr. Wharton Jones writes, “The 
proper membrane can be divided into two layers, an outer thin one, consisting of 
radiating fibres, and an inner thicker layer, which is less distinctly fibrous, though 
when torn it does indicate a fibrous disposition, and that in a direction opposite to 
the former The fibres which cross the radiating ones are also more aggregated 
at the centre. They run parallel with the handle of the malleus and turn round its 
extremity. At the circumference of the proper membrane there is a thick firm liga- 
mentous or cartilaginous ring, which is fixed in the groove of the bone. The liga- 
mentous ring appears to be formed by an aggregation of the circular fibres interwoven 
with the peripheral extremities of the radiating ones§.” 
By careful dissection the fibrous layers of the mernbrana tympani may be separated 
into two distinct laminae, the fibres of which have no communication with each other. 
The external layer may be called the radiate Jibrous lamina, on account of its fibres 
radiating from the malleus to be attached to the cartilaginous ring, and the internal 
the circular Jibrous lamina. The radiate layer is the thicker and stronger. So readily 
may the two layers be separated from each other, that they are detached with greater 
facility than that with which the circular layer can be removed from the mucous 
membrane. 
a. The Radiate Fibrous Lamina. 
If the whole of the mernbrana tympani be carefully removed, there will be observed 
at its circumference a white dense ring, apparently cartilaginous, which is received 
into the osseous groove of the temporal bone appropriated to it. It will be remem- 
bered however that this groove occupies only about five-sixths of the circumference 
of the inner extremity of the meatus, the upper sixth being smooth instead of grooved. 
* Loc. cit., p. 5. t P. 11. t Elements of Anatomy, fifth edition, 1848, vol. ii. p. 932. 
§ Cyclopsedia of Anatomy and Physiology, vol. ii. p. 545. 
