422 THE CORNEA, BY ALEXANDER ROLLETT. 



cells. Some of the cells appear granular, and contain a round 

 nucleus with a more or less well-defined contour; whilst 

 others, on the other hand, appear perfectly smooth and without 

 any indication of a nucleus. These two kinds of cells either 

 occur isolated or connected together into irregular figures, the 

 variations in the distribution of the two occasioning very 

 diverse markings of the endothelial membrane. 



DEVELOPMENT OF THE CORNEAL LAYERS BELONGING TO 

 THE CONNECTIVE TISSUE. 



The histogenesis of the cornea requires to be again worked 

 over, especially with the aid of the silver and gold methods of 

 preparation. At present our knowledge of this subject is very 

 fragmentary. Langhans* found in the cornea of the foetus of 

 a cow, one inch and a quarter long, elongated and roundish 

 cells, with not very sharply defined nuclei, lying in close 

 apposition. In an embryo with a length of one inch and a 

 half, the cells were irregularly roundish or angular in form. 

 In an embryo two inches and a half long, a fibrous appearance 

 was already visible in the teazed-out tissue ; the cells were large, 

 and their form resembled more closely the corpuscles of the 

 developed cornea. In the foetus of a Cow, the diameter of the 

 eye of which amounted to about 0'6 of a millimeter, the cells 

 were pale, elongated, and had from four to six processes. 



I have in my possession a series of meridianal sections of the 

 embryoes of Sheep hardened in Muller's fluid, tinted with 

 carmine, and imbedded in Peremeschko's solidifying mass. In 

 these I can see that the cornea is originally composed of round 

 cells in immediate contact with each other. Subsequently the 

 cells appear to be flattened towards the surface of the cornea 

 and lie superimposed one upon the other, like the cells in the 

 upper layers of laminated tesselated epithelium. 



A. clear substance intervenes between these flattened cells, 

 separating them from each other in the direction of the thickness 

 of the cornea, so that appearances are already produced re- 

 sembling those of the fully developed cornea. 



* Loc. cit., pp. 17 and 18. 



