THE PROPER TISSUE OF THE CORNEA; CORNEAL TUBES. 413 



cornea available for the demonstration of his nucleated plates 

 or laminae. How these come to be isolated will be considered 

 hereafter. 



We must now refer to the, as already stated, not certainly 

 proved system of canals lined with flattened cells, which Hoyer* 

 obtained by the silver method of preparation in that layer of 

 the corneal tissue of the Kitten, which is in immediate relation 

 to the membrana Descemetii ; which C. F. Miiller f states he 

 has seen in all the layers of the cornea in two embryoes of 

 the Cow, having a length of thirty- eight and forty-one milli- 

 meters, as well as in the Dog, Pig, and other animals, and 

 which, lastly, Schweigger-SeidelJ mentions, and has drawn as 

 it is seen in the Dog. 



This appearance I am well acquainted with, but I find it 

 only in young animals, and only well marked in the layers 

 close to the membrane of Descemet, as may be demonstrated 

 in any small Rabbit. 



Broad silver spaces, bulging at intervals, which are continu- 

 ous with each other by means of broad bridges, exhibit in their 

 interior sharply defined black lines, by which the silver spaces 

 are divided into areas having the same appearance as en- 

 dothelial or epithelial cells when bounded by a silver mark- 

 ing. The black lines correspond to actual cell boundaries. The 

 cells which meet in these lines are not plates, however, but 

 corneal cells, between which no fibrillar matrix, or but a very 

 sparing amount of it, is developed. 



The whole of the cornea at a certain period of development 

 consists of just such closely compressed and originally roundish 

 cells, and their development into corneal tissue proceeds from 

 the anterior towards the posterior surface of the cornea. In 

 young animals the same contour lines are presented in the 

 layers on the membrane of Descemet, which, during the de- 

 velopment of the cornea, are met with in all the other layers ; 

 and we there obtain the silver image described by Hoyer, as 

 has been stated by C. F. Miiller for the embryo of the Cow, 

 and as I have also observed in the embryoes of Sheep. 



* Reichert and Dubois-Reymond's Archiv, 1865, p. 214. 

 t Loc. cit., p. 132. 

 | Loc. cit., fig. 16. 



