770 SPECIAL HISTOLOGY. 



works, on the fibrous membrane and vitreous tunic of these parts, being 

 most abundant near the terminations of the nerves. Of these, we are 

 acquainted only with that of the acoustic nerve, which, with the nervus 

 vestibuli, supplies the three membranous canals and the elliptic sac- 

 culus, and, with a branch of the cochlear nerve, the round sacculus. 

 In the semicircular canals, the nerves are distributed only on the am- 

 pullae, and, indeed, enter each, as Steifensand has shown, in an inversion 

 or duplicature of the wall situated on the concave side of the canal, 

 which appears, viewed on the inside, as a transverse projection extend- 

 ing through about one-third of the circumference. Within these folds, 

 the nerves divide at first into two principal branches, which, diverging 

 towards both sides, penetrate into the vitreous membrane of the ampullae, 

 where each of them breaks up into a rich bundle of smaller, frequently 

 anastomosing ramuscules, which ultimately appear to terminate free, in 

 fine twigs, composed of from two to ten primitive fibres, 0-001-0-0015 

 of a line thick. In the sacculi, the distribution of the nerves is the 

 same, except that it occupies a larger space, and does not occur in a pro- 

 jection of the wall. In this situation, also, I think I have noticed free 

 prolongations of the attenuated nerves, although it may be very possible, 

 as Todd and Bowman point out, that they are continuous with very pale 

 fibres, in which they ultimately terminate. In the situation of the ner- 

 vous 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, 0-01 of 

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

 of Breschet, or otolithes, which are constituted of innumerable corpus- 

 cles, 0-0004-0-005 of a line long, and (in the largest) 0-001-0-002 of a 

 line 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 resi- 

 duum 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 scalce by a periosteum, here and there 

 presenting a small quantity of pigment, and which is constituted pre- 

 cisely like that of the vestibule, and also partially invests the lamina 

 spiralis ossea. An epithelium, 0-0005 of a line thick, with delicate, 

 flattened polygonal cells, 0-007-0-009 of a line in size, covers this liga- 

 mentous 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 canals, towards the free border of the lamina, 

 coalesce so as to form a fissure-like cavity and consequently, in this 

 situation, the osseous spiral lamina actually consists of two plates. 



