VISUAL ORGAN. 341 



surface of this epithelium is smooth, since the connective 

 tissue there is wanting in papillae. At the border of the 

 cornea this epithelium passes over into that of the conjunctiva. 



(2) The lamina elastica anterior (Bowman's membrane, 

 anterior basal membrane) is strongly developed in man, vary- 

 ing from 0.01 to 0.02 mm. in thickness. It is a homogeneous 

 refractive membrane. By means of certain reagents (potassium 

 permanganate) fibrillaB can be demonstrated in it. The anterior 

 surface presents minute inequalities, which correspond with 

 projections and depressions on the under surface of the basal 

 cells. 



(3) The substantia propria forms the main mass of the cornea. 

 It consists of connective-tissue fibrillse, which are bound 

 together into flat lamellas by means of interfibrillar cement 

 substance. There are in man about sixty of these lamella? 

 overlying one another and running parallel to the surface of 

 the cornea. They are joined together by interlamellar cement 

 substance. The fibrillse run in different directions and cross 

 one another at various angles. A few bundles run obliquely 

 and join the individual Iarnella3 with one another. These are 

 the so-called fibrce arcuatce. 



Through the entire substantia propria there runs a system 

 of canals and spaces which contain a serous fluid. This system 

 can be demonstrated most easily by impregnation with silver 

 or chloride of gold. The former gives a negative picture i. e., 

 the canals and spaces are colorless on a brown background. 

 By the gold method, on the contrary, a positive picture is 

 obtained, in which the canal system is colored violet (Fig. 

 260). In the spaces lie flat connective-tissue cells possessing 

 many processes and large nuclei. These so-called fixed cornea) 

 cells lie close to the walls of the spaces. Wandering cells also 

 occur in the cornea. 



(4) The lamina elastica posterior (Descemet's membrane, 

 posterior basal membrane) is a refractive membrane only 

 0.006 mm. thick. It has been described as an elastic mem- 

 brane, but, according to Mall, does not stain by Weigert's 

 elastic stain. 



