162 
MR. TOYNBEE ON THE STRUCTURE OF 
cartilage to the malleus these fibres interlace with each other, from whence originates 
the peculiar diamond-shaped markings observable on the outer surface of the mem- 
brane (fig. 6). When treated with acetic acid this lamina becomes opake, and some- 
times elongated oval nuclei are observed, the long axes of which correspond with the 
course of the fibres (fig. 7)- These nuclei are by no means invariably to be detected, 
and in several specimens they were not apparent on the application of the acid. In 
no instance was an oval nucleus visible in an isolated fibre. 
The circular white hand at the circumference of the radiate fibres consists of a firm 
mass of tissue, which is slightly elastic. It presents an indistinct appearance of fibres 
intermixed with oval-shaped nuclei. Upon the application of acetic acid this struc- 
ture loses its white aspect, becomes translucent, and discloses a greater number of 
the oval nuclei (fig. 8). 
b. The Circular Fihi'ous Lamina. 
This membrane is attached to the radiating fibres by fine cellular tissue, and, as 
previously stated, the two structures can be separated with facility ; the fibres of each 
lamina are quite distinct and never intermingle. The circular lamina consists, as its 
name implies, of circular fibres ; they are firm and strong at its circumference, but 
towards the centre they are so attenuated as to be detected only by considerable care. 
The strong fibres at the circumference of the layer form a complete circle, and are 
attached to each side of the body of the malleus and to the sides of the upper third 
of the process W.S longus (fig. 9). When carefully examined by a magnifying power of 
thirty to forty diameters, these circular fibres are observed to be intersected by others 
of an extremely delicate character; these delicate fibres are more numerous towards 
the central part of the lamina, where they are so intimately blended with the circular 
fibres that the latter are not easily distinguished (fig. 10). The central thin portion 
of the circular lamina is not attached to the malleus, but the fibres from each side 
are continuous, and they form a membranous layer composed of a series of concen- 
tric fibrous circles. The outer surface of this central portion of the lamina is in con- 
tact with the inner surface of the lower half of the long process of the malleus, to. 
which it is adherent by loose cellular tissue. The circular fibrous lamina is entirely 
unconnected with the cartilaginous ring into which the radiating fibres are inserted, 
but it is continuous with the periosteal lining of the tympanic cavity, of which it may 
be considered a modification. When the lamina of circular fibres is detached from 
that of the radiating fibres, it will be found to be slightly concave externally, though 
not to the same extent as the outer layer. In its separate condition it becomes rather 
less concave than when it was applied to the inner surface of the radiating fibres, and 
when its central portion is pressed inwards so as to increase its concavity, its inhe- 
rent elasticity causes it quickly to resume its former shape, resembling that of a 
saucer. If the two layers be detached from each other and placed side by side, the 
greater degree of concavity externally of the radiating fibrous layer is very perceptible. 
