556 



THE ORGANS 



(3) The substantia propria (Fig. 368, 3) constitutes the main 

 bulk of the cornea. It consists of connective tissue the fibrils of 

 which are doubly refracting and are cemented together to form 

 bundles and lamellae. In the human cornea the lamellae are about 

 sixty in number. The lamelhe are parallel to one another and to the 

 surface of the cornea, but the fibres of adjacent lamellae cross one 

 another at an angle of about twelve degrees. The lamellae are united 

 by cement substance. Fibres running obliquely through the 

 lamelhx from posterior to anterior elastic membranes hold the lamellae 

 tirmly together. They are known as perforating or arcuate fibres. 



■i-'^^^^-?^^^^ \A 



\B 





c 



Fig. 367. — Vertical Section through Sclera, Chorioid, and Pigment Layer of Retina. 

 (Merkel-Henle.) A, Sclera; B, chorioid; C, pigment layer of retina; d, lamina supra- 

 chorioidea; e, Haller's layer of straight vessels;/, choriocapillaris; g, vitreous membrane. 



Between the lamellae are irregular flat cell spaces which commu- 

 nicate with one another and with the lymph spaces at the margin of 

 the cornea by means of canaliculi. Seen in sections vertical to the 

 surface of the cornea, these spaces appear fusiform. In the spaces 

 are the connective-tissue cells of the cornea or corneal corpuscles. 

 These are flat cells corresponding in shape to the spaces and sending 

 out processes into the canaliculi (Figs. 369 and 370). 



(4) The posterior elastic membrane or membrane of Descemel 

 (Fig. 368, 4) resembles the anterior, but is much thinner. Like 

 the anterior, it does not give the chemical reaction of elastic tissue. 



(5) The posterior endothelium or endothelium of Descemet (Fig. 

 368, 5) consists of a single layer of flat hexagonal cells, the nuclei 

 of which frequently project slightly above the surface. 



The cornea contains no blood-vessels. 



The Chorioid. — This is made up of four layers which from 

 without inward are as follows (Fig. 367): 



