3*74 INTERNAL EAR OR LABYRINTH. 



end of the posterior, and one at the anterior end of the 

 horizontal. 



Membrane lining tlie Labyrinth. This membrane is fibro- 

 serous, and is to be distinguished from another to be 

 presently described, called the membranous labyrinth. It 

 resembles the dura mater in having an external and fibrous 

 layer, acting the part of periosteum, and adhering to the 

 bone, while its internal is free, smooth, and serous, se- 

 creting a fluid called the liquor Cotunnii, perilympli, or 

 aqua labyrinthi. This membrane lines the vestibule, coch- 

 lea, and semicircular canals; and also the fenestra ovalis, 

 and rotunda. The lamina spiralis also gets a covering 

 from it on either surface; and these two layers, coining 

 together at the free external margin of the osseous lamina, 

 pass to the outer wall of the tube, and thus complete the 

 septum between the two scalar It also sends processes into 

 the aqueducts of the vestibule and cochlea. 



The membranous labyrinth does not enter the cocKlea, 

 and is not so extensive as the osseous, though it has the 

 same form. It consists of four layers an external serous, 

 a vascular, a nervous, and an internal serous layer; thus 

 constituting a tube which floats between two fluids the 

 outer, the perilymph, or liquor of Cotunnius, secreted by the 

 external serous layer, and separating it from the walls of 

 the osseous labyrinth; and the inner, the liquor of Scarpa, 

 or endolympli, contained within the membranous tube of the 

 labyrinth itself, and secreted by its internal serous layer. 



The membranous labyrinth contains two sinuses, and 

 three membranous semicircular canals. The sinuses are 

 the common sinus, or vestibular ventricle, and the sacculus 

 proprius, or vestibuli. The common sinus is in the poste- 

 rior part of the vestibule, and receives the openings of the 

 five semicircular canals. It is distended by the liquor of 

 Scarpa, and floats in the fluid of Cotunnius. 



The sacculus proprius is situated anteriorly and inferi- 

 orly to the common sinus; it is round, and much smaller; 

 but it is not settled whether the two have any communica- 

 tion, though they are in close contact. 



