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of swallowing ; but during the first act, while they were open, air 

 was forced into the cavity of the tympanum by the contraction of 

 the muscles of the fauces and pharynx, and the orifices were again 

 closed, and remained so until the second act of swallowing, which 

 opened the tube and allowed the air to escape. That the act of de- 

 glutition opens the Eustachian tubes, was inferred also from the cus- 

 tom usually adopted of swallowing while the descent in a diving-bell 

 is performed ; by this act the condensed air is allowed to enter the 

 tympanum and the sensation of pain and pressure in the ears is 

 avoided. The author then proceeds to show that the tensor and levator 

 palati are the muscles which are attached to and open the Eustachian 

 tubes in man, and the mode in which they act is pointed out. 



Hie third part of the paper is devoted to the examination of the 

 Eustachian tube in animals ; and the author arrives at the conclusion, 

 that in Mammalia, Birds, and those reptiles having a tympanic cavity, 

 the Eustachian tubes, as in man, are closed excepting during muscular 

 effort. In some mammalia the muscles opening the tubes are, as in 

 man, those belonging to the palate ; in others the function is per- 

 formed by the superior constrictor of the pharynx. In birds it is 

 shown that there is a single membranous tube into which the two 

 osseous tubes open ; this membranous tube is situated between, and 

 intimately adherent to, the inner surface of each pterygoid muscle, 

 and by which muscles the tube is opened. 



The conclusion respecting the influence of the closed Eustachian tubes 

 to which the author arrives, is that the function of hearing is best 

 carried on while the tympanum is a closed cavity ; that the analogy 

 usually cited as existing between the ordinary musical instrument, the 

 drum and the tympanum, to the effect that in each it is requisite 

 for the air within to communicate freely with the outer air, is not 

 correct. The view that the sonorous vibrations of the air in a closed 

 tympanic cavity are more effective in impressing the membrane of 

 the fenestra rotunda than when it is open to the outer air, is strength- 

 ened by the performance of the following experiment with the tuning- 

 fork. If this instrument be made to vibrate by striking it against 

 a firm solid, and if the handle be then placed in contact with the 

 head, the sound at first loud, gradually becomes fainter, and soon 

 ceases to be heard ; if at the moment that it has ceased to be heard, 

 a finger be placed over the tragus of one ear, and firmly pressed so 

 as to close the external meatus from the outer air, the sound of the 

 tuning-fork is again heard, and continues to be heard for some 

 seconds ; thus showing that the sonorous undulations existing in 

 the external meatus are not sufficiently powerful to aflfect sensibly 

 the membrana tympani until they are wholly confined by the walls 

 of the tube when closed. 



The leading results arrived at in the paper are as follows : — 



1. That a principal function of the membrana tympani muscles 

 and ossicles of the tympanum, is to act as the analogue of the iris in 

 the eye, 



2. That the tensor tympani muscle, by drawing tense the mem- 

 brana tympani, and by compressing at the same time the fluid in the 



