744 



THE EYE AND VISION. 



[CH. LV. 



continuous all round. It is covered by stratified epithelium 

 (a, fig. 560), consisting of seven or eight layers of cells, of which 

 the superficial ones are flattened and scaly, and the deeper ones 

 more or less columnar. Immediately 

 beneath this is the anterior homogeneous 

 lamina of Bowman, which differs, only 

 in being more condensed tissue, from 

 the general structure of the cornea. 



The corneal tissue, as well as its 

 epithelium, is, in the adult, completely 

 destitute of blood-vessels ; it consists 

 of an intercellular ground-substance of 

 rather obscurely fibrillated flattened 

 bundles of connective tissue, arranged 

 parallel to the free surface, and forming 

 the boundaries of branched anastomos- 

 ing spaces in which the corneal cor- 

 puscles lie. These corneal corpuscles 

 have been seen to execute amoeboid 

 movements. At its posterior surface 

 the cornea is limited by the posterior 

 homogeneous lamina, or membrane of 

 Descemet, which is elastic in nature, 

 and lastly a single stratum of cubical 

 epithelial cells (fig. 563, d). 



Serves. The nerves of the cornea 

 are both large and numerous : they are 

 derived from the ciliary nerves. They 

 traverse the substance of the cornea, in 

 which some of them near the anterior 

 surface break up into axis cylinders, 

 and their primitive fibrillse. The latter 

 form a plexus immediately beneath the 

 epithelium, from which delicate fibrils 

 pass up between the cells anasto- 

 mosing with horizontal branches, and 

 forming an intra-epithelial plexus. Most 

 of the primitive fibrillae have a beaded 

 or varicose appearance. The cornea 

 has no blood-vessels penetrating its 

 structure, nor yet lymphatic vessels proper. It is nourished by 

 the circulation of lymph in the spaces in which the corneal 

 corpuscles lie. These communicate freely and form a lymph- 

 canalicular system. 



Kg. 563. Vertical section of rab- 

 bit's cornea, stained with gold 

 chloride, e, Stratified anterior 

 epithelium. Immediately be- 

 neath this is the anterior homo- 

 geneous lamina of Bowman, n, 

 Nerves forming a delicate sub- 

 epithelial plexus, and sending 

 up fine twigs between the epi- 

 thelial cells to end in a second 

 plexus on the free surface ; d, 

 Descemet's membrane, consist- 

 ing of a fine elastic layer, and 

 a single layer of epithelial cells ; 

 the substance of the cornea, /, 

 is seen to be fibrillated. and con- 

 tains many layers of branched 

 corpuscles, arranged parallel to 

 the free surface, and here seen 

 edgewise. (Schofield.) 



