XI. THE MIDDLE EAR OF INDIAN FROGS. 

 By Baini Prashad, M.Sc. 



(With Plate IX.) 



On each side of the head of the common frog the skin in the middle 

 of the temporal patch is distinguished as the tympanic membrane or 

 tympanum. The description of this structure in Rana temqioraria 

 may be given in the words of Marshall (13) : " Behind the eye on either 

 side is an obliquely placed elongated patch of a dark colour, in the middle 

 of which is a circular area — the tympanic membrane — supported by a 

 marginal ring." Other text books of Zoology in their accounts of R. 

 femporaria describe the condition in the same way as Marshall, while 

 soine say that the tympanic membrane is close to the surface and only 

 covered over with skin. 



Claus-Sedgwick (5) in the general account of the amphibia try to 

 get over the difficulty in the following way : " In the Eatrachians alone 



there is a tympanic cavity which is closed externally 



by a tympanic membrane, which is sometimes freely exposed on the 

 surface and sometimes covered by the skin." Boulenger (2 — 4) in his 

 systematic works describes the tympanum as distinct, indistinct or 

 hidden under the skin, according as the area of skin is marked off 

 from the surrounding skin or otherwise. Hoffman (12) is not definite 

 as to whether the tympanum is a structure distinct from the skin 

 covering it. Cope (6) states that there is a dermal membrana tympani 

 connected with the stapes through a chain of ossicula auditis ; evi- 

 dently he considers the tympanum to be a distinct structure from 

 the skin covering it, though he does not definitely say so. Crombie 

 (7) deals with the function and tension of the membrana tympani 

 of the mammals only. Fox (8) in his paper on the development of 

 the tympano-eustachian passage of the common American toad deals 

 with the development of the tympanic cavity, the eustachian tubes 

 and the ossicula auditis, but says nothing about the tympanum. 

 ViJly's admirable paper (16) on the development of the ear of the 

 European frog does not contain any reference as to the development of 

 this structure or its relations with the skin. Hasse in his two papers 

 (10, 11) deals with the structure of the internal ear of the frog only. 

 Norris (14) does not try to clear the problem. Retzius (15) is the 

 only author who has definitely stated that there is a distinct tympanic 

 membrane underlying the skin. Haslam in his translation of Ecker's 

 " Anatomy of the Frog " (9) has rewritten the whole section on the 

 ear from Retzius' paper cited above. 



From the review of literature on the subject it will be clear that a 

 great deal of confusion exists regarding the tympanum being a structure 

 distinct from the skin or otherwise. It was with a view to do something 



