Organ of Hearing. 



237 



The membranous laby- 

 rinth consists of two mem- 

 branous sacs, the Sacculus sphaeri- 

 cus or saccule (lying in the Reces- 

 sus hemispJiaericus vestibuli) and the 

 Sacculus ellipticus or utricle (lying 

 in the Recessus hemiellipticus) , in 

 which latter, the membranous 

 semicircular canals, cor- 

 responding to the bony, and also 

 containing ampullae, open. Bet- 

 ween the sacs, which do not com- 

 municate with each other, and the 

 inner surface of the bony labyrinth 

 lined by a thin periosteal mem- 

 brane, is a fluid, the Perilympha; 

 the membranous semicircular ca- 

 nals do not entirely fill out the 

 bony, in which they are lodged, 

 but lie only on the convex side of 

 the latter. The sacs and mem- 

 branous semicircular ca- 

 nals also contain a fluid, the 

 Endolymplia. Corresponding to the 

 three Maculae cribrosae and the 

 Pyramis vestibuli (places of entrance 

 of the N. acusticus) are rounded 

 bodies consisting of minute crystal- 

 line grains of carbonate of lime 

 (otoliths). The Nervus vestibuli pas- 

 ses through the foramina of the 

 three Maculae cribrosae, and its 

 fibres are distributed to the wall 

 of the membranous labyrinth, not 

 to its cavity. 



The internal auditory 

 meatus, commencing at the 

 posterior surface of the petrous 

 portion of the temporal bone, 

 ends by a blind pouch, being 

 separated from the vestibule 

 by a thin bony plate. The blind 

 pouch is divided by a bony ridge 

 into an upper and a lower fossa. 



325. The Membranous 



Labyrinth, (Diagrammatic.) 



/^A---- 77 



:: Ampulla - 

 Openings to t. /^ ~ Vv' J 



nf' -i ** -i x^L- -^ tttTL 



MacuL cmbros./^^ 

 Si 



Can. Folio 



. 



Tract, spiral, 

 foraminul. 



The End of the Inter- 

 nal Auditory Meatus. 



Magn. = 3. 



The upper has two depressions, the anterior leading to the Canalis Fallopiae, 

 the posterior to the Macula cribrosa superior; the lower has the Tractus 

 spiralis foraminulentus, behind this the openings to the Macula cribrosa media 

 and a larger opening to the Macula cribrosa inferior. 



Heitzmann, Atlas. I. 01 



