ANATOMICO-HISTOLOGICAL OBSERVATIONS. 



733 



The Visual Apparatus The Eye. 



384. HISTOLOGICAL OBSERVATIONS. In the following remarks it is 

 assumed that the student is familiar with the anatomical structure of the eye : 



The cornea, for the sake of simplicity, is regarded as uniformly spherical, although, properly 

 speaking, it differs slightly from this form. It is more like a vertical section of a somewhat 

 oblique ellipsoid, which we must suppose to be formed by rotating an ellipse around its long 

 axis (Briicke). It is nearly of uniform thickness throughout, only in the infant it is slightly 

 thicker in the centre, and in the adult slightly thinner. The cornea consists of the following 

 layers : 



[1. Anterior stratified epithelium. 4. Posterior elastic lamina. 



2. Anterior elastic lamina. 5. Single layer of epithelium.] 



3. Substantia propria. 



1. The anterior epithelium, stratified and nucleated, consists of many layers of cells (fig. 514, 

 a). The deepest cells are more or less columnar, are arranged side by side, and are called 

 supporting cells. The cells of the middle layers are more arched, and dip with finger-shaped 

 processes into corresponding spaces between their neighbours. The most superficial cells are 

 flat, perfectly smooth, hard, keratin- containing squamous epithelium. 2. The epithelial layer 

 rests upon the anterior elastic membrane (Bowman's elastic lamina), a structureless clear base- 



77 - 



Fig. 512. Fig. 513. 



Fig. 512. Cornea of the frog treated with chloride of gold, showing the corneal corpuscles 

 stained, and a few nerve-fibrils. Fig. 513. Cornea of the frog treated with silver nitrate ; 

 the ground substance is stained, while the spaces for the corneal corpuscles are left 

 unstained. 



ment-like membrane (&), whose existence is denied by Briicke. 3. The substantia propria of 

 the cornea consists of (chondrin-yielding) fibres composed of delicate fibrils of connective-tissue. 

 The fibres are arranged in mat-like thin lamellae (I), more or less united together, and are 

 placed in layers over each other. Towards the anterior elastic lamina, the fibres bend round 

 and perforate the superficial lamellae, thus serving as supporting fibres. [These perforating 

 fibres are comparable to Sharpey's fibres in bone.] Between the lamellae are a series of inter- 

 communicating spaces lined by endothelium. These spaces are really lymph-spaces, and they 

 communicate with the lymphatics of the conjunctiva. The fixed corneal corpuscles lie in these 

 spaces (c), and are provided with numerous processes, which anastomose with the processes of 

 corpuscles lying between the lamellae above and below, and on either side of them. Kiihne 

 observed that stimulation of the corneal nerves was followed by contraction of these cells ( 201, 

 7), while Kiihne and Waldeyer maintain that they are connected with the corneal nerve-fibrils. 

 [The corneal corpuscles are looked upon as branched connective-tissue corpuscles lying in 

 and not quite filling the branched spaces between the lamellae. The processes anastomose 

 freely with similar cells in the same plane, and to a less extent with the processes of cells in 



