SECTION II. 



AUDITORY CAVITIES, 



Read, June 28, 1819. 



The auditory apparatus consists^ 1st, of an assemblage of organs, 

 which serve, by their physical properties, to collect, transmit, and 

 modify, the immediate cause of the sense of hearing. — 2dly, of a 

 nerve destined to receive and convey to the brain the impressions of 

 sound. The cavities in the temporal bone, which are subservient 

 to these parts, may be called auditory ; and are naturally divisible, 

 according as they belong to the former or the latter, into the tympa- 

 num, with its appendages, and the labyrinth. 



The tympanum and its appendages offer to our consideration a great 

 number of parts, whose development must be separately considered. 

 On the external side of this cavity, we observe the external auditory 

 lube and the groove, in which the circumference of the membrane of 

 the tympanum is lodged ; on the internal, the oval hole, the round hole, 

 the promontory, and the pyramid ; — anteriorly, the canal which 

 lodges the internal muscle of the malleus, the eustachian tube, and 

 the partition which separates them ; — posteriorly, the mastoid cells 

 and their opening ; — superiorly and inferiorly, a number of little 

 sinuses, or caverns, bony fibres, &c. — and, finally, in the interior 



VOL. XIII. Y 



