CHAP.XVII1.] THE MEMBRANOUS LABYRINTH. 83 



less colouring matter disposed in irregular cells, exactly resembling 

 those figured at page 22, from the outer surface of the choroid coat 

 of the eye. We have not found a true epithelium on this surface. 

 The middle is the proper coat, and seems more allied to cartilage 

 than to any other tissue ; its limits are well marked, it is transpa- 

 rent, and exhibits in parts a longitudinal fibrillation : treated with 

 acetic acid, it presents numerous corpuscles or cell-nuclei. Where 

 it is thinnest it has a near resemblance to the hyaloid membrane of 

 the eye. The internal coat is composed of nucleated particles closely 

 apposed and but slightly adherent; the nuclei are often saucer- 

 shaped, and when seen edgeways have the uncommon appearance of 

 a crescent. They easily become detached and fall into the endo- 

 lymph. Minute arteries and veins, derived chiefly from a branch 

 of the basilar accompanying the auditory nerve, enter the vestibule 

 from the internal meatus, and ramify on the exterior of the mem- 

 branous labyrinth, apparently bathed in the perilymph. A beauti- 

 ful network of capillaries, forcibly reminding the observer of that 

 belonging to the retina, is spread out on the outer surface and in the 

 substance of the proper coat. These vessels have the simple homo- 

 geneous wall, interspersed here and there with cell-nuclei, that cha- 

 racterises the capillary channels in many other situations. There is 

 an abundant network of capillaries in the interior of the utriculus 

 and sacculus about the terminal distribution of the nerves, which 

 evinces the activity of the function of these parts. 



The membranous labyrinth, or its simple representative the audi- 

 tory sac, contains, in all animals, either solid or pulverulent calca- 

 reous matter, in connexion with the termination of the vestibular 

 nerves. This has been called by Breschet otolith, or ear-stone, when 

 solid, as in the osseous fishes, and otoconia, or ear-powder, when in 

 the form of minute crystalline grains, as in mammalia, birds, and 

 reptiles, but the former term may be conveniently employed to 

 designate both varieties. In the mammalia, including man, it is 

 found accumulated in small masses about the termination of the 

 nerves, both in the utriculus and sacculus, and we have found it 

 also sparingly scattered in the cells lining the ampullae and semicir- 

 cular canals. In the vestibular sacs, it appears to be entangled in 

 a mesh of very delicate branched fibrous tissue, in connexion with 

 the wall, and it is most probably held in place by cells within 

 which, according to Krieger,* its particles are deposited. It has a 

 regular arrangement, and is not free to change its place in the endo- 

 lymph. Otoliths consist always of carbonate of lime. 

 * De Otolithis, Berol. 1840. 



