THE VASCULAR TUNIC. 



341 



FIG. 387. Substantia prqpria stained with silver 

 to show the spaces containing the corneal cells. 

 X350. 



Canal of Schlemm 



anterior chamber. They are incompletely covered with endothelial cells and 

 enclose the spaces of Fontana. These spaces, better developed in lower 

 animals than in man, indirectly communicate with the aqueous chamber, and 

 thus form an important point for filtra- 

 tion of fluid from the interior of the 

 eye, by way of the canal of Schlemm, 

 into the anterior ciliary veins. 



The endothelium covers the 

 free inner surface of the posterior limit- 

 ing membrane. It consists of a single 

 layer of flat polygonal cells, whose 

 nuclei often extend above the level of 

 the cell-body. The cells are con- 

 nected by delicate protoplasmic proc- 

 esses and are continuous with the 

 cells lining the spaces of Fontana and 

 the anterior surface of the iris. With 

 Descemet' s membrane they constitute 

 a barrier to the filtration of fluid from 

 the anterior chamber into the cornea. 

 The blood-vessels of the normal 

 cornea are limited to a peripheral 

 zone, from 1-2 mm. in width, in which the terminal twigs of the episcleral 

 arteries end in loops. The remainder of the cornea is free from blood-vessels. 

 The nerves of the cornea are exceedingly numerous. They are branches of the 



long and short ciliary nerves, from 

 40 to 45 in number, and form an 

 annular plexus that surrounds the 

 margin of the cornea. Entering 

 the latter, they are accompanied 

 for a short distance by perineural 

 lymph-sheaths and, losing these 

 and their medullary substance, they 

 form a number of plexuses within 

 the corneal stroma at various 

 depths. A few of the fibres pass 



Fontana backwards and supply the pos- 



terior layers. Fully two thirds, 

 however, after forming a funda- 

 mental plexus, push forwards and 

 send perforating branches through 

 the anterior limiting membrane and 

 unite into a subepithelial plexus, the minute radial fibres passing towards the 

 centre of the cornea. From this plexus fibrils ascend between the epithelial 

 cells and end either as varicose fibrils, or in connection with special end-bulbs 

 (the intraepithelial plexus"}. After forming complex secondary plexuses, 

 branches from the fundamental plexus end within the substantia propria as 

 naked fibrillae between the lamellae. 



THE VASCULAR TUNIC. 



The middle or vascular coat, sometimes called the uveal tract, consists 

 of a connective tissue sheath supporting blood-vessels, which lies internal to 

 the outer fibrous tunic. It extends from the entrance of the optic nerve 



Y Traheculas of 



Spaces of pectinate ligament 



Bundles of ciliary muscle 



FIG. 388. Section through margin of anterior cham- 

 ber, showing spaces of Fontana, between the relaxed 

 trabeculae of the pectinate ligament, and the canal of 

 Schlemm. X 65. 



