538 



ORGAN OF HEARING. 



that the semicircular canals open into the am- 

 pullary dilatations and the vestibule. 



The common sinus is an elongated, laterally 

 compressed pouch, and lies in the posterior 

 part of the vestibule. It extends into the 

 upper horn to join the ampullae of the superior 

 vertical, and tof the horizontal semicircular 

 tubes ; and into the posterior and lower horn, 

 to join the ampulla of the posterior semicircular 

 tube, and to receive the tubulus communis 

 and cylindrical extremity of the horizontal 

 tube, as they emerge from their respective 

 canals. Its upper end, which is larger than 

 its lower, lies in the hemi-elliptical cavity, to 

 the bottom of which it is fixed by nervous 

 filaments. 



The membraneous tubes are only about a 

 third part of the calibre of the semicircular 

 canals in which they are contained. Like the 

 latter they are distinguished by the epithets, 

 superior vertical, posterior vertical, and hori- 

 zontal. Each membraneous semicircular tube 

 opens at one of its extremities, like its cor- 

 responding osseous canal, into an oval dila- 

 tation called ampulla, which on its part com- 

 municates with the common sinus. As the 

 vertical semicircular canals unite at one of 

 their exiremities to form the common canal, 

 so their corresponding membraneous tubes 

 also unite to form a common tube, tubulus 

 communis, which occupies the common canal. 



At the place where the nervous filaments 

 enter the common sinus, its wall presents a 

 much more considerable thickness and consist- 

 ence than elsewhere. 



According to Steifensand,'* who has ex- 

 amined the structure of the ampullae very 

 carefully, each ampulla presents a very much 

 arched surface, superficies convexa, and op- 

 posite to this a concave or indented surface, 

 superficies concava s. inftexa, which receives 

 the nervous filaments. Where the nerve enters 

 there is a transverse depression, sulcus trans- 

 versus, by which this surface is divided into 

 two parts. This transverse depression on the 

 outside produces in the interior a fold of the 

 membrane composing the wall of the ampulla, 

 and through which the nerve enters. This 

 fold forms a transverse septum, septum trans- 

 versum, which divides the interior of the am- 

 pulla into two parts ; one of which, the sinus 

 part, communicates by the osteum sinus with 

 the common sinus, and the other, the tube part, 

 by the osteum tubuli with the membraneous 

 tube. 



Saccule, sacculus rotundas. This is a round 

 membraneous bag, smaller than the common 

 sinus in front of which it lies in the hemisphe- 

 rical depression of the vestibule. It is firmly 

 fixed in its place by nervous filaments which 

 proceed to it through the apertures observed 

 in the bottom of the hemispherical depression. 

 As has been mentioned in regard to the com- 

 mon sinus, the wall of the saccule presents an 

 increase of thickness and consistence at the 

 place where the nervous filaments enter it. 



* Muller's Archiv. fur Anat. Physiol. und wis- 

 senschaftl. Medecin. 1835. Heft. II. pp. 173, 174. 



Small in the Mammifera, the saccule is very 

 distinct and large in fishes. 



The common sinus and saccule adhere to 

 each other, but whether their cavities com- 

 municate has not been determined. They are 

 fixed, as has been said, to the inner wall of the 

 vestibule, by the nervous filaments which they 

 receive through the apertures with which that 

 part is perforated. Towards the outer wall 

 they are nowhere in contact with the base of 

 the stapes, the perilymph intervening. This 

 circumstance, first distinctly pointed out by 

 Scarpa,* and particularly insisted on by Bre- 

 schet, shows that it is only by the intermedium 

 of the perilymph that the movements of the 

 stapes can have any impression on the nervous 

 expansions of the membraneous labyrinth. 



The common sinus, ampullae, semicircular 

 tubes, and saccule are composed of a firm trans- 

 parent membraneous coat,within which is a ner- 

 vous expansion, and outside which is a cellulo- 

 vascular layer, in some places tinged black or 

 brown. Of the nervous expansion we shall 

 speak under the head of the auditory nerves. 

 In the sheep, hare, rabbit, &c. the walls of 

 the membraneous labyrinth present patches of 

 black pigment, a circumstance noticed by 

 Scarpa,f Comparetti,} and Breschet. Before 

 I knew of the observations of these anatomists 

 I had myself observed the fact. I was not, 

 however, led to the discovery of it by accident ; 

 but, being engaged in researches on the pig- 

 ment of the eye, and considering the analogy 

 which the organs of sense bear to each other 

 in their general anatomical structure, I was 

 curious to know whether pigment did not exist 

 also in the ear. Examination proved to me 

 that it did ; for I found, as Scarpa and Com- 

 paretti had previously noticed, pigment de- 

 posited in the form of small black spots in the 

 membraneous parts of the labyrinth in dif- 

 ferent Mammifera. In some I have found a 

 distinct cellulo-vascular layer of a black or 

 brown colour forming the outer surface of the 

 membraneous labyrinth. And, contrary to 

 what Breschet asserts, I have found pigment 

 in the membraneous labyrinth of the human 

 ear also. It appears, especially on the am- 

 pullae, under the form of a slight but perfectly 

 distinct brown tinge, similar to what is seen 

 around the ciliary processes in the eyes of 

 Albinos. 



Semicircular tubes are found in all the Ver- 

 tebrate animals, with the single exception of 

 the Cyclostomata. When they do exist there 

 are never more nor less than three. 



The common sinus, ampullae, semicircular 

 tubes, and saccule contain a limpid humour. 

 Suspended in this humour there is found in 

 the common sinus and also in the saccule a 

 small mass of calcareous powder. 



The liquid of' the membraneous labyrinth, 



* Anatomicae disquisitiones de Auditu et Olfactu, 

 s. xvi. p. 55. 



t Op. cit. s. iv. p. 49. 



t Observat. Anatom. dc aure interna comparat. 

 p. xxxii. Praefat. 



Op. cit. 



