CORNEA. 371 



connected by an interlamellar cement substance, and by occasional oblique 

 fiber-bundles. The latter so-called arcuate fibers are to be found especially 

 between the anterior layers. In the cement substance, there is a system of 

 branched canaliculi, dilated in places to form oval spaces. The latter are 

 between lamellae but the canaliculi extend among their constituents fiber- 

 bundles. Within the spaces there are flat stellate anastomosing cells, the 

 branches of which extend into the canals and tend to unite with those of 

 neighboring cells at right angles. The cells and their processes are more 

 or less surrounded by tissue fluid. Leucocytes enter the canals and are 

 normally found in the cornea; if the cornea is inflamed they become abun- 

 dant. Blood vessels and lymphatic vessels are absent. 



The posterior basal membrane [Descemet's membrane] is a clear 

 elastic lamina, 6 , thick. Its inner surface in the adult shows hemispher- 

 ical elevations. The mesenchymal epithelium is a simple layer of flat 

 polygonal cells. The iris sends connective tissue prolongations over the 

 peripheral part of the inner corneal surface. Collectively they are called 

 the ligamentum pectinatum of the iris. As compared with those of the ox 

 and horse, in man they are rudimentary. 



BLOOD VESSELS. 



The central vessels of the retina supply a part of the optic nerve and 

 the retina; the ciliary vessels supply the rest of the eye. These two sets 

 of vessels anastomose with one another only at the entrance of the optic 

 nerve (Fig. 42 5). 



The ciliary arteries are (i) the short posterior ciliary arteries to the 

 chorioid; and (2) the long posterior ciliary arteries which with (3) the 

 anterior ciliary arteries supply chiefly the ciliary body and iris. The three 

 groups will be considered in turn. 



1. After supplying the posterior half of the surface of the sclera, 

 some twenty branches of the short posterior ciliary arteries penetrate 

 the sclera around the optic nerve. They form the capillaries of the 

 lamina choriocapillaris. At the entrance of the optic nerve they anasto- 

 mose with branches of the central artery of the retina (c) and thus form 

 the circulus arteriosus nervi optici. At the ora serrata they anastomose 

 with recurrent branches of the long posterior ciliary and the anterior 

 ciliary arteries. 



2. The two .long posterior ciliary arteries also penetrate the sclera 

 near the optic nerve (i). They pass, one on the nasal and the other on the 

 temporal side of the eye, between the chorioid and sclera to the ciliary body. 

 There each artery divides into two diverging branches extending along the 



