18 



THE EYE. 



index of refraction, so that in the perfectly fresh condition it is difficult, even with 

 the best lenses, to make out any indications of structure. After death, however, 

 and with the assistance of reagents, the cornea may be ascertained to consist of 

 alternating lamellge of fibrous tissue (about sixty in number, according to Bowman), 

 the planes of which are parallel to the surfaces of the cornea. The fibres com- 

 posing the lamellae are nearly straight and have a definite direction in each layer ; 

 they cross one another at right angles in the alternate layers (fig. 19, b,d). It must, 

 however, be understood that the layers are not individually distinct, but give off 

 frequent offsets to those above and below, so that they cannot readily be stripped 

 away for any distance. The fibrils are collected into roundish bundles, which, as 



Fig. 18. VERTICAL SECTION THROUGH THE EPITHELIUM OP THE CORNEA, HUMAN. (E. A. S.) 



Highly magnified. 



c, deepest columnar cells ; p, polygonal cells, immediately above them ; /, flattened cells of the 

 surface. 



The section is slightly broken on the right of the rigure. The intercellular channels bridged across 

 by processes extending from one cell to another are distinctly seen. 



well as the laminae they form, are, as in the connective tissue elsewhere, separated 

 from each other by ground-substance. The latter is in greater abundance between 

 the fibrous strata than elsewhere, and in these parts the cell-spaces of the tissue are 

 found. These cell- spaces, which are readily demonstrated by staining the tissue 

 with nitrate of silver (fig. 20, B), are flattened conformably with the lamellae, are of an 

 irregularly stellate figure, and freely communicate by their offsets both with others 

 on the same plane and with those above and below. The greater regularity of 

 arrangement which characterises them, as compared with the cell-spaces of con- 

 nective tissue elsewhere, is dependent on the regularly laminated structure of the 

 cornea. 



The corpuscles of the tissue corneal corpuscles (fig. 20, A) lie within the cell- 

 spaces, corresponding generally with them in form, but without entirely filling them, 

 the room left serving for the passage of lymph and lymph-corpuscles. The protoplasm 

 of the corpuscles is clear, except in the neighbourhood of the nucleus, where it is 

 more granular ; the cells send branching processes along the anastomosing canals of 

 the cell-spaces, which join with those of neighbouring corpuscles. In vertical 

 sections the corpuscles appear fusiform (fig. 19, c), but horizontal sections show 

 them to be flattened conformably with the surface. 



The cell-spaces can be filled with fluid injection by inserting- the nozzle of a fine syringe 

 into the tissue, and employing 1 a very low pressure ; in this way a network of anastomosing 

 stellate figures is obtained (cell-spaces, Recklinghausen's canals). If, however, the injection- 

 fluid is dense or too forcibly injected, it becomes extra va sated in the interstices of the 

 fibril-bundles, the direction of which it takes ; and the appearance is produced of minute 

 swollen tubular passages running at right angles to one another in the different layers 

 (Bowman's corneal tubes). This appearance may still more readily be obtained if air is 

 injected into the tissue instead of mercury (the fluid used by Bowman), and it is seen 



