ORGANS OF THE SENSES. 527 



" Continuous with the thin margin of the osseous zone is 

 the membranous zone. (Plate LXIX.^. 4.) This is a trans- 

 parent glassy lamina, having some resemblance to the elastic 

 laminas of the cornea, and the capsule of the lens. A narrow 

 belt of it, next the osseous zone, is smooth, and exhibits no 

 internal structure, while, in the rest of its width, it is marked 

 by a number of very minute straight lines, radiating out- 

 wards from the side of the modiolus. These lines are very 

 delicate at their commencement, become more strongly 

 marked in the middle, and are, again, fainter ere they cease, 

 which they do at a curved line on the opposite side. Beyond 

 this, the membranous zone is, again, clear and homogeneous, 

 and receives the insertion of the cochlearis muscle. The 

 inner clear belt of the membranous zone is little affected by 

 acids : it seems hard and brittle. The middle or pectinate 

 portion is more flexible, and tears in the direction of the lines. 

 The outer clear belt is swollen, and partially destroyed by the 

 action of acetic acid. Along the inner clear belt, and on its 

 tympanic surface, runs a single, sometimes branched vessel, 

 which would be most correctly called a capacious capillary, 

 as it resembles the capillaries in the texture of its wall, but 

 exceeds them in size. It is the only vessel supplied to the 

 membranous zone, and seems to be thus regularly placed, 

 that it may not mar the perfection of the part as a recipient 

 and propagator of sonorous vibrations. 



Of the Cochlearis Muscle. "At its outer or convex 

 margin, the membranous zone is connected to the outer wall 

 by a semitransparent structure. This gelatinous-looking 

 tissue was observed by Breschet, and is, indeed, very obvious 

 on opening the cochlea ; but we are not aware of any one 

 having hinted at what we regard to be its real nature. The 

 outer wall of the cochlea presents a groove, ascending the 

 entire coil, opposite the osseous zone of the lamina spiralis, 

 and formed principally by a rim of bone, which, in section, 

 looks like a spur, projecting from the tympanic margin of the 

 groove, the opposite margin being very slightly or not at all 

 marked. This groove diminishes in size towards the apex 

 of the cochlea. It gives attachment to the structure in 



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