THE MEMBRANA TYMPANI IN THE HUMAN EAR. 
163 
Structure of the Circular Lamina. 
When highly magnified, the fibres composing the circular lamina are found to be 
smaller than those constituting the radiate fibrous layer ; they vary in size from the 
6000th to 10,000th of an inch in breadth. The outer fibres run parallel with each 
other, and do not interlace so much as the radiating fibres ; they are diaphanous, and 
do not present any wavy longitudinal lines (fig. 1 1). When acetic acid is applied the 
fibres enlarge and assume a certain degree of opacity, and in some instances this 
lamina also has presented distinct oval nuclei, elongated in the direction of the fibres 
(fig. 12). Like the radiate lamina, the separate fibres were never observed to reveal 
the existence of nuclei, and as a general rule their presence in the tissue is not de- 
tected. 
It is often not easy to decide whether a structure is muscular, and doubts may 
arise as to the real nature of the two fibrous laminee of the rnembrana tympani. My 
own researches do not seem to favour the vievv of that membrane being a contractile 
tissue. 
The facts which seem to militate against the idea of its being muscular are, — 
1st. The absence of distinct nuclei in the fibres. 
2nd. Their great denseness and hardness, their firm and unyielding structure, 
they being so strong that it is with some difficulty they can be torn across. 
The mucous membrane forming the inner layer of the rnembrana tympani is in 
the healthy ear so extremely thin that its presence is with difficulty detected ; by 
careful dissection however it can nevertheless be removed entire from the inner- 
surface of the circular fibres, to which it is connected with considerable firmness by 
fine cellular tissue. 
It will now be evident that of all the laminae which constitute the rnembrana 
tympani not one is proper to the organ, all of them being directly continuous with 
other structures, of which they appear to be modifications*. Thus: — 
1st. The epidermis is continuous with that lining the external meatus. 
2nd. The radiate fibrous lamina is a prolongation of the periosteal lining of the 
external meatus. 
3rd. The circular fibrous lamina is a prolongation of the periosteum of the 
tympanum. 
4th. The layer of mucous membrane fortns part of the lining of the tympanic 
cavity (fig. 13). 
Previous to considering the functions of the fibrous laminae of the rnembrana tym- 
pani, it is desirable to advert to another point in the structure and relations of this 
organ. It has been already stated that the rnembrana tympani is attached at its 
circumference to the temporal bone, and at its central part to the malleus. The 
* See Appendix. 
Y 2 
