DEVELOPMENT OF THE PROPER TISSUE OF THE CORNEA. 423 



This separation of the cells from one another does not occur 

 uniformly in all the layers of the cornea. It commences near 

 the anterior pole of the eye, affects the anterior layers first, 

 and then extends progressively backwards towards the anterior 

 chamber. 



At a certain period of development this layer is separated from 

 the corneal layer with already fully developed intermediate 

 substance by a layer of flattened cells superimposed one upon 

 another, the innermost of which exactly resemble the cell layer 

 corresponding to the endothelium of the membrane of Descemet. 

 The membrane of Descemet is not as yet present. It occurs as 

 a slender stria between the innermost cell layer and the cells 

 forming plates superimposed one upon the other situated more 

 externally. 



In the embryo of a Calf eight centimeters long, and in human 

 embryoes of the second or third month, the membrane of Des- 

 cemet presents, according to Donders,* the same structureless 

 appearance as in adult animals, except that it is thinner. 



In the clear substance which, as mentioned above, separates 

 the flattened cells of the developing tissue of the cornea, fine 

 fibrils or fasciculi of fibrils occur at a very early period. The 

 cells themselves appear to be provided with processes which 

 radiate from them in all directions, and anastomose with the 

 processes of neighbouring cells, but which, as is shown by 

 teazed-out preparation and by sections, are never continuous 

 with the substance of the fibrils.f The latter occur in the 

 material occupying the interspaces of the granular protoplasm 

 of the cells, in the same manner as the fibrils of the connective 

 tissue in the development of the plexus 4 The histological 

 processes taking place in the cornea of Rabbits after the 

 anterior layers have been shaved off, and in the cornea of Man 



* Nederlandisch Lancet, August, 1851, p. 47. 



f See Wilckens, Ueber die Entwicklung der Hornhaut des Wirbelthie) - 

 auges, (On the development of the cornea of the eye of vertebrate animals, ) 

 Zeitschrift fur rationel. Medicin, 3 R., Band xi., p. 167. 



See this Manual, Vol. i., p. 84. 



Bonders, HoUandische Beitrage zur Natur- uud Hellkunde, Band i., 

 p. 387. De Gouvea, Archiv fur Augen- und Ohrcu-iicilkunde, Band i., 

 p. 119. 



