ORGAN OF HKAKING. 



537 



osseous labyrinth is remained an extremely 

 delicate and complicated niciulitano - ner- 

 vous apparatus, called j MmfcwMPM ///- 

 riiitli, tirst properly described by Scarpa.* 

 It does not extend into all the compartments 

 of the osseous labyrinth, but only occupies the 

 vestibule and semicircular canals. The coch- 

 lea, as has been said, contains in its cavity 

 nothing but penlymph. 



The vestibular part of the membraneous 

 labyrinth, and of that perhaps one of the 

 pouches only, is all that is really fundamental 

 in the structure of an oruan of hearing. In 

 the ( rustacea and Cephalopodous Mollusc a in 

 which the organ of hearing exists in its sim- 

 plest form, and even in the Cyclostomatous 

 fishes there is nothing but a small pouch con- 

 taining a little liquid and a lapilliform body. 



Much smaller than the cavities which con- 

 Jain it, the membraneous labyrinth is sus- 

 pended as it were in the perilymph. It does 

 not appear to adhere to the walls of the laby- 

 rinthic cavity except at the points where it re- 

 ceives nervous filaments. 



The component parts of the membraneous 

 labyrinth are: 



1. The common sinus. 2. The membrane- 

 ous ampullae and semicircular tubes. 3. The 

 saccule. 



Fig. 238. 



A magnified representation of the left ustcinu Inhy- 

 ritith Itiiil ii/ ( ( M /c *h"ir tlu 1 inftnbrantuna labyrinth 

 in its situation. (From Krcschet.) 



a. membraneous ampulla o!' the ampullhry sinus 

 <it the ;inu-iior srinu imilar canal ; /. membrane- 

 ous ampulla of the ampullary sinus of the external 

 semicircular canal; r. mmbrtnaoui iniipulhi of 

 the ampuliary sinus of tin: juMrin'i si micin ular 

 canal ; d. anterior nwmhnuieottl srmii imiUr tube; 

 f. rvii'iiui! rniTiilH.iiii tuis si-micircular tube; f. 

 push n. r iiHinbrjucmis semicircular tube ; g. com- 



* De auditu 9t olfauu. 



mun membraneous lube resulting from tlie junction 

 of 'I"- lubes '/ anil / ; h. the place where the ex- 

 ternal mrniUram'uus semicircular tube opens into 

 lite common sinus ; i i. common sinus filling a 

 great pan of the vestibule ; k. a small mass of 

 calcareous powder shining through its w.ills ; / /. 

 saccule, also continuing, m. another mass of cal- 

 careous powder ; n a neivou* fasciculus, furnishing, 

 i:. aa r\p.iii~iu to the anterior membraneous am- 

 pulla y p. another to the ampulla of the external 

 tube, and q . & third to the common sinus ; r. ner- 

 vous fasciculus to the laccule ; another fasciculus 

 of nervous filaments, not lettered, is seen going to 

 the ampulla of the posterior membraneous semi- 

 circular tube; i a. spiral lamina; *'. the termin- 

 ation of the spiral lamina in the hamulus ; t. com- 

 mencement of the scala tympani near the fenestra 

 rotunda, which is here no longer seen ; u. com- 

 mencement of the scala vestibuli ; x. extremity of 

 the Axis around which the termination of the spiral 

 lamina turns ; y y. a bristle engaged in the hcli- 

 cotrcma ; z. place where the summit of the axis 

 is continued into the wall of the osseous labyrinth ; 

 tr w to, membraneous portion of the spiral lamina, 

 particularly broad in the last turn, (lettered w u 

 in the figure instead of tftrtr); *** spaces 

 between the walls of the labyrinthic cavity and 

 membraneous labyrinth occupied by the peri- 

 lymph. 



Fig. 239. 



The left membraneous labyrinth isolated together with 

 tfa nerves. Magnified. (From Bretchet.) 



a. ampulla of the anterior semicircular tube ; 

 6. ampulla of the horizontal semicircular tube ; 

 c. ampulla of the posterior ftcniicircuUr tube , it. 

 common tube ; e, mass of calcareous particles 

 lying in the common sinua; /. the sacculc nui- 

 taining also a mass of calcareous particles ; k. 

 porlio dura of the seventh pair ; m. nervous fila- 

 ments to the ampulla of the anterior semicircular 

 tube i n. liUments to the ampulla of the hori- 

 zontal semicircular tube ; filaments arc also (teen 

 going to the ampulla of the postrrior semicircular 

 tube, not lettered ; o. lilaments to the common 

 sinus; q. filaments to the saccule ; r. cochlear 

 nerve. 



The cvinrunn sinus, niemhntnroits (irnpulfo, 

 and MwAfVMM *< micircittar tubes. These 

 constitute but one apparatus which is just the 

 counterpart of the vestibule, ampullary sinus* s, 

 and seni.cin ular canals of the osseous laby- 

 rinth; the B6m .circular tubes opening into the 

 ampulla? and common sinus in the same way 



