THE EYE. 355 



composed principally of a soft, laminated epithelium,, 0023 — 

 0-050"' thick, in which the deeper layers of cells are elongated 

 and placed vertically upon the cornea, whilst the middle ones 

 are more of a rounded form, and as they approach the surface, 

 pass into a layer, 0008 — 0*0 1/" thick, corresponding to the 

 horny layer of the epidermis, composed of plates 001 — 0'14/" in 

 size, though still nucleated and soft. Many of these latter cells, 

 as I have shown (' Zeitsch. f. wiss. Botanik/ II, p. 80), in conse- 

 quence of their mutual pressure, present larger or smaller pits, 

 like certain cells in the urinary bladder, so as when viewed on 

 the side often to exhibit a stellate figure, which induced 

 Valentin, who first noticed this form, to regard them as cells 

 with processes. Beneath the epithelium, which, after death, 

 is very soon rendered opaque by both water and acetic 

 acid, is a structureless lamella, first described by Bowman 

 (anterior elastic lamella, of Bowman), 0*003 — 0-004'" thick, 

 which is especially evident in vertical sections and in folds of 

 thin superficial sections, upon the addition of alkalies, although 

 it is by no means so sharply defined from the true cornea as 

 the membrane of Descemet, nor does it seem to be of the 

 same import as that membrane, but is perhaps no more than 

 the remainder of the vascular layer of the corneal conjunctiva, 

 which exists at an earlier period. Arched fibres, like rigid 

 bundles of connective tissue or elastic fibres, are occasionally 

 visible, given off from it, and penetrating the cornea to a certain 

 distance, where they are lost. 



The membrane of Descemet or Demours, also termed the 

 membrane of the aqueous humor (memb. Descemeti, s. Demoursii 

 s. humoris aquei) (fig. 296 d), consists of an elastic membrane 

 rather laxly attached to the corneal tissue — the proper mem- 

 brane of Descemet [posterior elastic lamina of the cornea, 

 Bowman], and of an epithelium on its inner surface. The 

 former is as clear as glass, brilliant, quite structureless, easily 

 lacerable though tolerably firm, and so elastic, that when it is 

 raised from the cornea by the scalpel and forceps, by boiling in 

 water, or by maceration in alkalies, under which treatment, as 

 under reagents in general, it does not lose its transparency, it 

 always rolls up strongly and towards the front. Towards the 

 border of the cornea, the membrane of Descemet, which is 

 0-006 — 0-008'" thick, and in chemical properties approaches 



