969 



1. Epidermis. 



2. The proper fibrous layer, composed of — 



a. The lamina of radiating fibres. 



b. The lamina of circular fibres. 



3. Mucous membrane. 



One of the principal objects of the paper is to describe the struc- 

 ture and functions of the fibrous laminae. Since the time of Sir 

 Everard Home, who pronounced the layer of radiating fibres to be 

 muscular, anatomists have differed in their views of the nature of the 

 fibrous element of the membrana tympani. The lamina of radiating 

 fibres, the outer surface of which is covered by the epidermis, is 

 described as continuous witii the periosteum of the external meatus. 

 With the exception of the uppermost fibres, which on account of 

 their being somewhat flaccid have been considered as a separate 

 tissue under the name of " membrana fiaccida," the radiate layer is 

 composed of fibres which extend from the circular cartilaginous ring 

 to the malleus^ and they interlace in their course. These fibres are 

 from the 4000th to the 5000th part of an inch in breadth. 



The lamina of circular fibres consists of circular fibres, which are 

 firm and strong towards the circumference, but very attenuated 

 towards the centre. These fibres are so attached and arranged as 

 to form a layer of membrane, which in a quiescent state is saucer- 

 shaped. The fibres composing the circular are smaller than those 

 of the radiate lamina, being from the 6000th to the 10, 000th part 

 of an inch in breadth. 



The facts that appear to be adverse to the idea of the fibres of 

 either layer being muscular are — 



1. The absence of distinct nuclei in the fibres. 



2. Their great denseness and hardness. 



It is next shown that the four laminae forming the membrana tym- 

 pani are continuous with other structures, of which they appear to 

 be mere modifications, and that not one is proper to the organ. 



The tensor tympani ligament, which had not been previously 

 noticed by anatomists, is particularly described ; it is attached ex- 

 ternally to the malleus, close to the insertion of the tensor tympani 

 muscle, and internally to the cochleariform process. 



The latter part of the paper is occupied by observations on the 

 functions of the fibrous laminae and of the tensor ligament of the 

 membrana tympani ; and it is shown that by these two antagonistic 

 forces, the one tending to draw the membrana tympani inwards, the 

 other outwards, this organ is maintained in a state of moderate ten- 

 sion, and is always in a condition to receive ordinary sonorous un- 

 dulations, 



6. "Investigations into the Structure and Development of the 

 Scales and Bones of Fishes." By W. C. Williamson, Esq. Com- 

 municated by W. B. Carpenter, M.D., F.R.S. 



In this memoir the author first points out the discrepancies that 

 exist between the opinions of M. Mandl and M. Agassiz respecting 

 the structure and growth of cycloid and ctenoid scales ; and after 



