THE EYE AND ITS APPENDAGES. 



337 



mous in character ; it is thinnest over the central part of the cornea, 

 where its six to eight layers of cells together measure about 45 /*, at 

 the periphery reaching almost double that thickness. The deepest 

 cells are columnar in form with their outer ends somewhat rounded 

 off, while their bases are slightly expanded and conform to the surZ 

 face of the basement-membrane upon which they rest. Succeeding 

 the deepest layer the elements become 

 broader and polyhedral, many pos- FIG. 362. 



sessing the protoplasmic threads char- 

 acteristic of prickle-cells. The su- 



perficial strata are composed of 

 flattened cells which lie parallel to 

 the surface and contain oval nuclei. 



The anterior limiting mem- 

 brane, membrane of Bowman, or 

 lamina elastica anterior, corre- 

 sponds to a highly-developed base- 

 ment-membrane, being continuous 

 with the tissue of the substantia pro- 

 pria, of which it is a special conden- 

 sation. The structure is especially 

 conspicuous in the human cornea, 

 where it appears as a seemingly ho- 

 mogeneous glassy layer, about 20 M 

 in thickness in the middle of the cor- 

 nea, gradually diminishing towards the 

 periphery. The resolution of this 

 lamina into delicate connective- 

 tissue fibrillse after treatment with 

 suitable reagents demonstrates its 

 true nature as a specialized portion of 

 the substantia propria. 



The fibrous stroma, or the sub- 

 stantia propria, constitutes the chief 

 bulk of the cornea, and is made up 

 of parallel lamellae composed of in- 

 terlacing bundles of fibrous connective tissue. The exact num- 

 ber of corneal lamellae is inconstant, since this depends upon the 

 extent to which the artificial separation of the tissue is carried. The 

 interlacing bundles of the white fibrous tissue composing the 

 lamellae are united by the interfibrillar cement substance, and cross 

 one another obliquely at various angles, the adjacent bundles being 

 intimately united by bands, the fibrse arcuatse, which pass from 

 one bundle to the other ; the arcuate fibres are especially prominent 



22 





Section of human cornea : a, anterior 

 epithelium ; c, anterior limiting membrane ; 

 b, b, fibrous substantia propria, containing 

 corneal corpuscles (f) lying within cor- 

 neal spaces ; d, posterior limiting mem- 

 brane ; e, endothelium lining anterior 

 chamber. 



