238 NORMAL HISTOLOGY. 



ules. On the external surface the sclera sends off 

 delicate fibres anteriorly into the subconjunctival 

 tissue, while posteriorly, behind the muscle-tendons, 

 they join to form the wall of a lymph-sac, called the 

 capsule of Tenon. On the inner surface certain 

 fibres pass directly over into the choroid ; others 

 form the outer wall of a lymph-sac between the 

 sclera and choroid, and called, on account of its 

 yellow color, the lamina fusca ; it resembles in 

 structure the outer layers of the choroid, presently 

 to be described as the membrana siipra-clwroidea, of 

 which it is indeed a part. In man and many animals, 

 the opening in the posterior segment of the sclera, 

 through which the optic nerve passes, is crossed 

 by a net-work of connective-tissue fibres ; these pass 

 in from the sclera on all sides, and surround the 

 delicate bundles of nerve-fibres of the opticus, form- 

 ing the lamina cribrosa. 



THE CORNEA. 



The cornea is directly continuous at its periphery 

 with the sclera, but differs from it in structure in 

 many particulars, among the more prominent of which 

 are, the more regular lamellar arrangement of its con- 

 nective-tissue basement-substance, the greater trans- 

 parency of the latter, the peculiar form of its cellular 

 elements, and the free surfaces covered with cells. 



In a thin section of the cornea, perpendicular to 

 its surface, we recognize, passing from before back- 



