THE CORNEA. 893 



The conjunctival epithelium, which covers the front of the cornea proper, 

 consists of several strata of epithelial cells. The lowermost cells are columnar : 

 then follow two or three layers of polyhedral cells, some of which present ridges 

 and furrows similar to those found in the cuticle. Lastly, there are three or four 

 layers of scaly epithelium with flattened nuclei. 



The proper substance of the cornea is fibrous, tough, unyielding, perfectly 

 transparent, and continuous with the sclerotic, with which it is identical in 

 structure. It is composed of about sixty flattened lamellae, superimposed one on 

 another. These lamellae are made up of bundles of fibrous connective tissue, the 

 fibres of which are directly continuous with the fibres of the sclerotic. The fibres 

 of each lamella are for the most part parallel with each other ; those of alternat- 

 ing lamellae at right angles to each other. Fibres, however, frequently pass from 

 one lamella to the next. 



The lamellae are connected with each other by an interstitial cement-substance, 

 in which are spaces, the corneal spaces. The spaces are stellate in shape, and 

 have numerous offsets by which they communicate with other spaces. Each space 

 contains a cell, the corneal corpuscle, which resembles in form the space in which 

 it is contained, but does not entirely fill it. 



Immediately beneath the conjunctival epithelium the cornea proper presents 

 certain characteristic differences, which have led some anatomists to regard it as a 

 distinct membrane, and it has been named by Bowman the anterior elastic lamina. 

 It differs, however, from the true elastic lamina or membrane of Descemet in 

 many essential particulars, presenting evidence of fibrillar structure, and not 

 having the same tendency to curl inward or to undergo fracture when detached 

 from the other layers of the cornea. It consists of extremely closely interwoven 

 fibrils, similar to those found in the rest of the cornea proper, but contains no 

 corneal corpuscles. It seems, therefore, more proper to regard it as a part of the 

 proper tissue of the cornea. 1 



The posterior elastic lamina, which covers the proper structure of the cornea 

 behind, presents no structure recognizable under the microscope. It consists of a 

 hard, elastic, and perfectly transparent homogeneous membrane, of extreme thin- 

 ness, which is not rendered opaque by either water, alcohol, or acids. It is very 

 brittle, but its most remarkable property is its extreme elasticity, and the tend- 

 ency which it presents to curl up or roll upon itself, with the attached surface 

 innermost, when separate from the proper substance of the cornea. Its use 

 appears to be (as suggested by Dr. Jacob) " to preserve the requisite permanent 

 correct curvature of the flaccid cornea proper." 



At the margin of the cornea this posterior elastic membrane breaks up into 

 fibres to form a reticular structure at the outer angle of the anterior chamber, 

 the intervals between the fibres forming small cavernous spaces, the spaces of 

 Fontana. These little recesses communicate with a somewhat larger space in the 

 substance of the sclerotic close to its junction with the cornea. This is the canal 

 of Schlemm, or sinus circularis iridis, and, according to some authors, is a lymph- 

 canal, but according to others is a venous sinus. Some of the fibres of this 

 reticulated structure are continued into the front of the iris, forming the liga- 

 mentum pectinatum iridis, while others are connected with the fore part of the 

 sclerotic and choroid. 



The endoiheKal fining of the aqueous chamber covers the posterior surface of 

 the posterior elastic lamina. It consists of a single layer of polygonal flattened 

 transparent nucleated cells, similar to those found lining other serous cavities. 



Arteries and Nerves. The cornea is a non-vascular structure, the capillary 

 vessels terminating in loops at its circumference. Lymphatic vessels have not as 

 yet been demonstrated in it, but are represented by the channels in which the 

 bundles of nerves run ; these are lined by an endothelium and are continuous 

 with the cell-spaces. The nerves are numerous, twenty-four to thirty-six in 



1 This layer has been called by Reichert the " anterior limiting layer " a name which appears 

 more applicable to it than that of "anterior elastic lamina." 



