THE LABYRINTH. 447 



are the canals for transmitting the filaments of the portio mol- 

 lis or auditory nerve. 2. The Zona Coriacea, on the outer 

 side of this, the structure of which is cartilaginous. 3. The 

 Zona Vesicularis, said to contain in its cells a pellucid fluid. 

 4. The Zona Membranacea, which is probably only the l+ning 

 membrane of the cochlea, and .completes the lamina spiralis on 

 its edge next to the periphery of the cochlea. Some very re- 

 spectable anatomists pass over this minute distinction in the 

 structure of the septum, and merely divide it into Zona Ossea, 

 and into Zona Mollis* 



Of the Membranous Labyrinth. 



The whole internal face of the bony Labyrinth is lined by 

 a very delicate and vascular membrane, which is more dis- 

 tinct during the early periods of intra uterine life. Besides 

 this, there is a membranous labyrinth, consisting in three semi- 

 circular canals, nearly filling up the cavities, and having the 

 same shape and general arrangement of the bony canals; and 

 in two sacs contained in the vestibule. 



The Semicircular Membranous Canals have also at their 

 ends the elliptical enlargements called ampullae; they termi- 

 nate by both extremities in the sac of the superior part of the 

 vestibule. This sac is generally called, from its shape, Sac- 

 culus Elliptieus; and by Scarpa, from its function, the Alveus 

 Communis. In front of the Sacculus Elliptieus, nearer the 

 cochlea, and opposite the foramen ovale, is the Sacculus Sphe- 

 ricus; it is a complete bag, having no communication with the 

 other, or with the membranous canals. Both of the sacs ad- 

 here to the vestibulum at their posterior parietes. 



The sacs of the vestibule and the membranous semicircular 

 canals are filled with a very fluid transparent liquid. Accord- 

 ing to the observations of JVL Ribes, it is not necessary to the 

 function of hearing that this fluid should be so abundant as to 

 distend the membranous labyrinth, inasmuch as in his dissec- 

 tions he met with individuals in whom the latter was only half 

 filled, and yet they had heard very well. He also met with 

 similar cases in which the fluid was abundant in the vestibu- 

 lum, but deficient in the canals, and the reverse. Correspond- 



