444 



Lrana tympani by operation. In one of them, it was supposed that 

 a sti'ucture of that nature was brought into view, but, iu the other 

 two, nothing of that kind could be seen or felt. By a comparison 

 of the external appearances in the last-mentioned individuals, with 

 observations made in the dissection of similar cases, and more espe- 

 cially from the examination of a specimen preserved in the Anatomi- 

 cal INIuseum of the University of Edinburgh, the author formed the 

 conclusion, that, in the majority of such cases, the complete closure 

 of the bony part of the meatus opposes an insuperable obstacle to 

 their relief by surgical operation ; and that the malformation visible 

 externally, indicates the existence of other defects iu the deeper or 

 middle portion of the organ of hearing. These defects consist in the 

 small size and unnatural shape and structure of the cavity of the 

 tympanum ; the imperfect condition of the chain of small bones ; the 

 impossibility of these bones fulfilling their usual office from the 

 absence of their connection with a membrana tympani ; and probably 

 other defects of stn;cture, such as that observed in the specimen 

 preserved in the Edinburgh Museum, which seems important, as con- 

 sisting in a contracted state of the fenestra rotunda, and the want of 

 direct communication of that orifice with the cavity of the tympanum, 

 such, in fact, as woidd occasion an interrujition of the transmission of 

 vibrations through the aii" of the tymi>anum to the Huid of the laby- 

 rinth. It does not appear probable, that the Eustachian tube is 

 entirely absent in such cases ; ])ut the size of its opening into the 

 tympanum is probably much diminished in most of them. In most 

 of such cases, the labyrinth or internal ear appears to be natural 

 The defective condition of the bony parts in these cases then 

 appears to consist mainly in the absence of a part of the tympanic 

 boue, that, namely, which intervenes between the fissure of Glaser 

 and the mastoid process, and which forms the tympanic ring and 

 auditory process of the temporal bone. 



In the second part of the paper, the author endeavoured to ex- 

 plain the origin of the malforma;tion in question, by a reference to 

 the ascertained history of the development of the external and 

 middle parts of the organ of hearing in the ftetus of man and ani- 

 mals : founding his conclusions more particularly upon the researches 

 of Huschke, Eathke, Eeichert, Gilnther, and his own observations 

 in this point of organo-genesis. From these, it appeared that mal- 

 formations of the external and middle ear are, in a great measure, 

 unconnected in their origin or progress with those of the labyrinth ; 

 and that, while the latter are related to the earliest changes of for- 



1 



