THE EAR. 407 



minate. In the situation of the nervous expansion, we find, in 

 each of the sacculi, a sharply defined spot, as white as chalk, 

 and readily seen by the naked eye, which is attached to the 

 inner wall of the sacculus by a perfectly clear membrane, 001'" 

 thick, and probably epithelial. These are the so-termed 

 otoconia of Breschet, or otolithes, which are constituted of 

 innumerable corpuscles, 0*0004 — 0*005 "' long, and (in the 

 largest) 0001 — 0002'" broad, of a rounded or elongated 

 form, or distinctly pointed at each end, probably hexahedral 

 prisms, suspended in a homogeneous substance. They are 

 composed of carbonate of lime, and are said to leave a residuum 

 of some organic matter; but this I have not succeeded in 

 observing. 



§ 235. 



Cochlea, — The canal of the cochlea, filled by the fluid of 

 the labyrinth, is lined in both its scala by a periosteum, here 

 and there presenting a small quantity of pigment, and which 

 is constituted precisely like that of the vestibule, and also par- 

 tially invests the lamina spiralis ossea. An epithelium, 00005"' 

 thick, with delicate, flattened polygonal cells, 0*007 — 0*009'" in 

 size, covers this ligamentous membrane, and is also continued 

 upon the lamina spiralis membranacea, where its nature is, to 

 some extent, altered. The most important part of the cochlea 

 is the lamina spiralis, which, in its osseous zone, contains 

 narrow-meshed anastomosing canals for the reception of the 

 cochlear nerves, which canaJs, towards the free border of the 

 lamina, coalesce so as to form a fissure-like cavity and conse- 

 quently, in this situation, the osseous spiral lamina actually 

 consists of two plates. The membranous zone, having a con- 

 stant width of 0*2'", is again subdivided into a zona den- 

 ticulata and a zona pectinata, the former of which constitutes 

 about the inner two thirds, and the latter the outer third of the 

 breadth of the membranous lamina, and are both characterised 

 by a great complexity of structure, the importance of which 

 was first, in more recent times, pointed out by Corti (/. c.) 

 (vid. figs. 309, 310). 



1. The zona denticulata (d-v) may be again subdivided into 

 two portions, an internal, the habenula interna s. sulcata [d-g), 

 and an external, the habenula externa s. denticulata (h-t). The 



