HUMAN ANATOMY. 



FIG. 1207. 



Canal of Schlemm 



bands, which are especially numerous in the anterior lamellae, to which the name 

 fibres arcuata; has been given. The fibrillae and bundles are held together by an 

 amorphous cement substance, and embedded in it are the cellular elements, the 

 corneal corpuscles. These are flattened connective tissue cells, with faintly granular 

 protoplasm, the nuclei of which in the adult are irregular and show nucleoli. The 

 cells are provided with branching processes which anastomose with those of other 

 cells both on the same level and with those between adjacent lamelke, and so con- 

 stitute a continuous net-work of protoplasm, upon which the nutrition of the cornea 

 largely depends. They have been described as occupying part of a regular system 

 of cell-spaces and canaliculi, but most recent investigations seem to indicate that 

 during life they fill out the spaces completely, and leave no gaps through which 

 fluid can pass. Occasionally leucocytes or wandering cells are found between the 

 fibrous elements. 



The posterior limiting membrane, also known as Descemcf : s membrane, the 

 membrane of Demours, or the posterior elastic membrane, is a practically homo- 

 geneous band, which varies in thickness from .006 .012 mm. at the center and 

 at the periphery respectively. It is less firmly united to the substantia propria than 

 is the anterior limiting membrane, and is less easily affected by acids, alkalies, boiling 



water and other regents. It resembles 

 elastic tissue and is very firm and resist- 

 ant to injury or perforation from inflam- 

 mation. At the periphery, Descemet's 

 membrane splits up into bundles of fine 

 fibres, which are gradually strengthened 

 and form a scries of firm connective 

 tissue trabeculae, some of which form 

 the point of attachment of the ciliary 

 muscle ; others run into the iris, and still 

 others constitute the outer wall of a 

 circularly disposed venous channel, the 

 sinus circularis iridis, or canal of 

 Schlemm. These fibres are known as 

 the ligamentum pectinatum iridis 

 and form the outer boundary of the angle 

 of the anterior chamber. They are 

 incompletely covered with endothelial 

 cells and enclose between their loose meshes the spaces of Fontana. These, 

 better developed in lower animals than in man, directly communicate with the anterior 

 chamber, and thus form an important path for filtration of fluid from the interior of 

 the eye, by way of the canal of Schlemm, into the anterior ciliary veins. 



The posterior endothelium covers the inner surface of Descemet's membrane. 

 It is composed of a single layer of flattened polygonal cells, the nuclei of which often 

 extend above the level of the cell body. The cells are connected together by deli- 

 cate protoplasmic processes and are continuous with the cells lining tin- spaces of 

 Fontana and the anterior surface of the iris. With Descemet's membrane they con- 

 stitute a barrier to the filtration of fluid from the anterior chamber into the cornea, 

 although its passage by diffusion is possible. 



The blood-vessels of the normal cornea are limited to a peripheral zone, 

 from i-2 nun. in width, where the terminal twigs of the episcleral branches of 

 the anterior ciliary arteries end in loops (Fig. 1215), from which the blood is 

 carried to the anterior ciliary veins. The remainder of the cornea is free from 

 blood-channels. 



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

 the long and short ciliary nerves, from 40 to 45 in number, and form a plexus which 

 surrounds the margin of the cornea i plexus anmiluris). Those which supply the 

 anterior part of the cornea anastomose first with the conjunctival nerves. Entering 

 the cornea, they are accompanied for a distance of r mm. by a perineural lymph- 

 sheath, and then losing this and their medullary sheath, they form within the corneal 

 stroma a number of plexuses at various depths. A few of the fibres pass backward 



Trabeculae of 



pectinate 



ligament 



Bundles of ciliary muscle 



Meridional section through angle of anterior chamber 

 showing spaces of Fontana between relaxed fibres of 

 pectinate ligament and canal of Schlemm. X 65. 



