TUNICA FIBROSA OCULI. 451 



At the periphery that is, at the edge of the cornea Descemet's 

 membrane goes over into the fibers of the ligamentum pectinatum. 



The endothelium of Descemet's membrane consists of low, quite 

 regular hexagonal cells, which in certain vertebrates (dove, duck, 

 rabbit) are peculiar in that a fibrillar structure may be seen in that 

 portion of each cell nearest the posterior elastic membrane. By 

 means of these fibers, not only adjacent cells, but also those further 

 apart, are joined together. Thus we have here to a marked degree 

 the formation of fibers which penetrate the cells and connect them 

 with one another, conditions already met with in the prickle-cells 

 of the epidermis. 



The cornea is nonvascular. In fetal life, however, the capil- 

 laries from the anterior ciliary arteries form a precorneal vascular 

 network immediately beneath the epithelium, a structure which is 

 obliterated shortly before birth and only rarely seen in the new- 

 born. Its remains are found at the corneal limbus either as an 

 episcleral or conjunctival network of marginal capillary loops. Fine 

 branches of the anterior ciliary arteries extend superficially along 

 the sclera to the corneal margin, and form here a network of capil- 

 laries also ending in loops, from which numerous veins arise, con- 

 stituting a corresponding network emptying into the anterior ciliary 

 veins. The conjunctival vessels likewise form a network of mar- 

 ginal loops at the corneal limbus, and are connected with the epi- 

 scleral vessels (Leber). Under pathologic conditions the cornea 

 may become vascularized from the marginal episcleral network. 



The nerves of the cornea are derived from the sensory fibers of 

 the ciliary nerves, which form a plexus at the corneal margin ; from 

 this, nonmedullated fibers penetrate the cornea itself and form two 

 plexuses, a superficial and a ground plexus ; the latter is distributed 

 throughout the whole substantia propria with the exception of its 

 inner third (Ranvier, 81). The two plexuses are connected by 

 numerous anastomoses. At one time it was supposed that direct 

 communication existed between the corneal corpuscles and the nerve- 

 fibers of both plexuses. This view, however, contradicts the gen- 

 erally accepted neurone theory. 



Nerve-fibers from the superficial plexus pass through the ante- 

 rior, elastic membrane and form a plexus over the posterior surface 

 of the epithelium, known as the subcpithelial plexus. From the lat- 

 ter nerve-fibers extend between the epithelial cells, terminating in 

 telodendria with long slender nerve-fibrils, which end in small 

 nodules. Many of the fibrils reach almost to the surface of the 

 epithelium (Rollet, 71 ; Ranvier, 81 ; Dogiel, 90). 



Smirnow (1900) has described a rich nerve -supply for the sclera, 

 consisting of both medullated sensory fibers and nonmedullated 

 sympathetic fibers, derived mainly from the ciliary nerves. The 

 sympathetic fibers supply the blood-vessels; the sensory fibers ter- 

 minate in free endings between the connective-tissue lamellae. 



