THE SOLERA AND CORNEA 



1093 



Structure (Fig. 798). The cornea consists of five layers namely: (1) the anterior or epi- 

 thelial layer; (2) the anterior elastic layer; (3) the substantia propria; (4) the posterior elastic 

 layer; (5) the posterior or endothelial layer. 



1. The anterior layer (epithelium corneae) is composed of stratified epithelium and is contin- 

 uous with the cells of the conjunctiva at the borders of the cornea. There are from five to eight 

 strata of nucleated cells in the 



anterior layer. The deepest cells ^^^BK^t'V^^ Tf'yi j> iPBBMHfcfc ^Anterior 

 are columnar. Above the columnar I ^ epithelium 



cells are several layers of polygonal 

 cells, most of which have finger- 

 like processes and are called prickle 

 cells. At the surface the cells and 

 nuclei become flat. 



2. The anterior elastic or ante- 

 rior limiting layer, or Bowman's 

 membrane (lamina elastica ante- 

 rior'], is less than half the thickness 

 of the layer of stratified epithelium. 

 It resembles in some respects, but 

 is not, elastic tissue. It shows evi- 

 dences of fibrillary structure, and 

 does not display a tendency to curl 

 inward or to undergo fracture 

 when detached from the other 

 layers of the cornea. It consists of 

 extremely close interwoven fibrils, 

 similar to those found in the rest 

 of the cornea proper, but contains 

 no corneal corpuscles. It ought, 

 therefore, to be regarded as a part 

 of the proper tissue of the cornea, 

 apparently representing a base- 

 ment membrane. 



3. The substantia propria or 

 proper substance of the cornea 

 forms the main thickness of that 

 structure. It is fibrous, tough, un- 

 yielding, perfectly transparent, and 

 continuous with the sclera. It is 

 composed of about sixty flattened 

 lamellae, superimposed one on 

 another. These lamellae are made 

 up of bundles of modified connec- 

 tive tissue, the fibres of which are 

 directly continuous with the fibres 

 of the sclera. The fibres of each 

 lamella are for the most part 

 parallel with each other; those of 

 alternating lamellae at right angles 

 to each other. Fibres, however, 

 frequently pass obliquely from one 

 lamella to the next (fibrae arciiatae). 



The lamellje are connected with 

 each other by an interstitial cement 

 substance, in which are spaces, the corneal spaces (Fig. 799). The spaces are stellate in 

 shape, and have numerous offshoots or canaliculi (Fig. 799), by which they communicate with 

 each other. Each space contains a cell, the corneal corpuscle (Fig. 799), which resembles in 

 form the space in which it is lodged, but it does not entirely fill it, the remainder of the space 

 containing lymph. In the aged the margin of the cornea becomes opaque gray. This rim is 

 called the arcus senilis, and is due to fat deposit in the lamella* and corneal corpuscles. 



4. The posterior elastic lamina, the membrane of Descemet, or of Demours (lamina elastica 

 posterior], which covers the posterior surface of the substant^ propria of the cornea, presents 

 no structure recognizable under the microscope. It consists <>. Rustic, and perfectly trans- 

 parent homogeneous membrane, of extreme thinness, which is ifonm^idered opaque by either 

 water, alcohol, or acids. It is very brittle, but its most remarkable property is its extreme elas- 

 ticity and the tendency which it presents to curl up, or roll upon itself, with the attached surface 



Posterior 

 epithelium 



FIG. 798. Vertical section through the cornea of a newborn child. 

 X 200. (Szymonowicz.) 



