THE MEMBRANA TYMPANI IN THE HUMAN EAR. 
167 
Appendix to a Paper “ On the Structure of the Memhrana Tympani in the Human Ear." 
.Bz/ J oseph Toynbee, F.R.S., Fellow of the Royal College of Surgeons of England, 
Aural Surgeon to St. Mary's Hospital, and Consulting Surgeon to the St. George's 
and St. James's General Dispensary. 
In a note at p. 161 of the above paper, I have stated that the blood-vessels 
ramifying in the upper part of the membranous lining of the external meatus are 
freely continuous with those of the memhrana tympani. These blood-vessels are con- 
nected by cellular tissue, and the two together often form a distinct layer of mem- 
brane, covering the outer surface of the upper part of the radiate fibrous lamina 
(fig. 4).” Since writing the above lines I have had opportunities of making several 
careful dissections of the membrane alluded to, and the result of these dissections is 
to demonstrate that between the epidermoid and radiating fibrous layers of the mem- 
brana tympani, there is a distinct and complete lamina of membrane which is conti- 
nuous with the dermoid layer of the meatus. The presence of this membrane, to 
which, on account of its structure and functions, I have given the name of dermoid 
layer, is best demonstrated by carefully dissecting under water the membranous 
meatus from the upper surface of the osseous tube as far as the attachment of the 
membrani tympani ; at this point the periosteum of the meatus is seen to become con- 
tinuous with the radiate fibrous lamina; this being cut through, the dermoid layer is 
seen passing down over the outer surface of the radiate fibres, and separating them 
from the epidermis. If the upper portion of this layer be drawn gently downwards 
by one hand, by means of a fine needle in the other, the delicate cellular tissue con- 
necting it to the fibrous lamina can be broken up and it may be removed entire. The 
presence of the dermoid lamina may also be shown by the introduction of a fine bristle 
between it and the radiating fibrous layer, at the superior part of the memhrana 
tympani, and then by passing it down the cellular tissue is lacerated. 
In a healthy state, when uninjected by blood or by artificial means, the dermoid 
lamina is thin and transparent ; examined by the microscope its structure is found to 
resemble areolar tissue. When injected, this membrane is observed to have numerous 
blood-vessels ramifying through it, and they form an elaborate plexus; when these 
vessels are enlarged, they give the red appearance to the surface of the memhrana 
tympani which is so frequently met with during life. It is upon the supply of nerves 
to this membrane that the exquisite sensibility of the memhrana tympani depends. 
A knowledge of the existence of the membrane here deseribed is of interest to the 
anatomist, who recognizes in it the secreting organ of the epidermoid layer of the 
memhrana tympani', and to the surgeon, who by its presence is able to understand 
phenomena occurring in certain diseases of the ear which have been hitherto incom- 
prehensible to him. Figure 17 is illustrative of the structure of the memhrana tympani. 
