542 



THE NERVOUS SYSTEM. 



watch itself. It is the segment of a smaller sphere than the 

 sclerotic. Its anterior surface is convex and covered by conjunc- 

 tiva, its posterior surface concave, the curvature being less in old 

 age. It is composed of four layers (Fig. 321) : (1) Stratified epi- 

 thelium, next to the conjunctiva. (2) A thin layer of connective 

 tissue, membrane of Bowman. (3) Fibrous connective tissue, proper 

 substance of the cornea, which is made up of fibers arranged in 

 lamellae, those of each of the sixty bundles being at right angles 

 with those of the lamellae above and below it. Between the 



Blood-vessels 

 V2in. Canal of Petit, of the iris. Cor 



Sphincter 

 pupillae. Iris. 



Fontana's spaces. 



Physiologic excavation. 



Macula lutea. 



FIG. 320. Schematic diagram of the eye : a, vena vorticosa ; b, choroid ; I, lens 

 (after Leber and Flemmiiig). 



lamellae, and connecting them, is a cement substance, and in this 

 are the stellate corneal spaces, each of which contains a corneal 

 corpuscle, *\vhich gives off branches that form with the processes 

 of other corpuscles a continuous network. This third layer is of 

 the same character as the sclerotic coat, and is continuous with it. 

 (4) Membrane of Descemet or Demours\ an elastic layer which, near 

 the junction of the cornea with the iris, separates into fibers, 

 ligamentum pectinatum. Some of these exist in the iris as its 

 pillars. The fourth layer is covered by pavement epithelium, 

 epithelium of Descemet's membrane. This epithelium forms, there- 



