CH. LVL] 



THE CORNEA 



767 



muscular fibres, called the capsule of Tenon. The innermost layer of 

 the sclerotic is made up of loose connective tissue and pigment-cells, 

 and is called the lamina fusca. 



The cornea is a transparent membrane which forms a segment of 

 a smaller sphere than the rest of the eye- 

 ball, let in, as it were, into the sclerotic, 

 with which it is continuous all round. It 

 is covered by stratified epithelium (a, fig. 

 562), 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 

 rest of the cornea. 



The rest of the cornea consists of many 

 layers of connective tissue fibres arranged 

 parallel to the free surface, the direction 

 of the fibres crossing one another at right 

 angles in the alternate laminae. The 

 corneal corpuscles lie in branched anasto- 

 mosing spaces between the laminae. They 

 have been seen to execute amoeboid move- 

 ments. 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. 

 565, d). 



The nerves of the cornea are both large 

 and numerous : they are derived from the 

 ciliary nerves. They traverse the sub- 

 stance of the cornea, in which some of 

 them near the anterior surface break up 

 into axis cylinders, and their primitive 

 fibrillae. The latter form a plexus im 

 mediately beneath the epithelium, from 

 which delicate fibrils pass up between 

 the cells anastomosing 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 or lymphatics, but 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. 



FIG. 565. Vertical section of rabbit's 

 cornea, stained with gold chloride. 

 e, Stratified anterior epithelium. 

 Immediately beneath this is the 

 anterior homogeneous lamina of 

 Bowman, n, Nerves forming a 

 delicate sub-epithelial plexus, and 

 sending up fine twigs between the 

 epithelial cells to end in a second 

 plexus on the free surface; d, 

 Descemet's membrane, consisting 

 of a fine elastic layer, and a single 

 layer of epithelial cells; the sub- 

 stance of the cornea, /, is seen to 

 be fibrillated, and contains many 

 layers of branched corpuscles, ar- 

 ranged parallel to the free surface, 

 and here seen edgewise. 



(Schofield.) 



