280 SPECIAL ANATOMY. 



communicate in the lamina terminalis through an opening in the 

 membrane which separates them (see before). 



Aquceductus cochlece (Cotugno) opens into the scala tympani 

 close before fenestra rotunda, and opens on the other side on the 

 inferior border of the petrous bone close to fossa jugularis. 



Both the aqueduct of the cochlea and vestibule are at last regarded as ca- 

 nals for small veins. Arnold, however, thinks still that they serve as vent 

 canals. The delicate membrane with which they are lined passes over into 

 the dura mater and the periosteum of the petrous bone. 



515 3. The membranous labyrinth. 



In the interior of the labyrinth, which is covered with a-delicate 

 vascular membrane (charoidea labyrinthi, Arnold), we find a wa- 

 tery fluid (aqua Cotunnii, Perilympha), in which but only in 

 the vestibule and the semicircular canals a whitish, transparent 

 nervous membrane is suspended (labyrinthus membranaceus]. 

 The last forms in the vestibule two, in the semicircular canals three 

 sacs filled with the aquula vitrea. Zona Valsalvce (see before) 

 separates the two scales, the humor aqueus of which flows through 

 the opening at the lamina terminalis [helicotrema] from the one 

 into the other. 



a. Canales semicirculares membranacei, far more narrow, but otherwise 

 similar to the osseous semicircular canals, in which they lie, they are ex- 

 panded in the internal crura (ampullae) and open with five orifices into the 



b. Vestibulum membranaceum. This consists of two portions. 



1. Sacculus oblongus (s. utriculus ventricularis) receives alone the five 

 semicircular canals, is larger than 2., lies in the recessus hemiellipticus, 

 separated from the Stapes only by the aq. Cotunnii. 



2. Sacculus rotundus is much smaller, lies in the recessus hemisphericus 

 under the former without communicating with it, and the n. saccularis 

 minor spreads out in it. 



c. Aquula vitrea (Scarpce) s. Endolympha; rather a thicker fluid than the 

 aq. Cotunnii, fills up the membranous tubes and sacs of the labyrinth and con- 

 tains a fine crystalline deposit. 



Otoconia, sand of the ear, otolithi, stones of the ear ; these are smaller or 

 larger accumulations of six-sided columns consisting of carbonate of lime, and 

 an organic material (Huschke) which in the vestibule adhere opposite to the 

 expansion of the nerves, and serve for the strengthening of the sounds. 

 Larger and more distinct in the lower classes of animals (and in the embryo) 

 their structure, in man, in spite of the researches of Breschet, Krieger, and 

 others, is not yet determined. 



Vessels and nerves of the labyrinth. Artt. cochleae and vestibuli are branches 

 of art. audiloria interna, and correspond to the 



