NERVES OF THE CORNEA. 431 



cornea, whilst towards the external surface the nerves become 

 more and more delicate, and the meshes of the plexus smaller 

 (fig. 390). 



The whole plexus in Mammals occupies essentially the two 

 outer thirds of the thickness of the cornea. A few isolated 

 fibres only supply those parts of the cornea that lie nearer the 

 membrane of Descemet, and these run backwards from the 

 marginal parts of the innermost portion of the anterior plexus 

 formed by the largest nerve fibres. Kolliker states that in 

 Rabbits he has observed the fine lines emanating from these 

 fibres running in a horizontal direction along the membrane of 

 Descemet, and at a short distance from it. 



Several subdivisions may be distinguished in the plexus oc- 

 cupying the anterior parts of the cornea. For whilst the 

 thicker nerves proceeding from the posterior parts of the cornea 

 gently bend forward, they expand, together with finer branches, 

 which for the most part run parallel to the surface at a short 

 distance from the line of demarcation between the corneal 

 tissue and the external epithelium (internal to the anterior 

 limiting layer), to form a superficial plexus, enclosing uniform 

 meshes. Emanating from this plexus, delicate vertical or 

 slightly inclined branches (rami perforantes) run to the an- 

 terior surface of the cornea and to the anterior epithelium, 

 immediately subjacent to which they break up, either in the 

 form of a brush, as in the Guinea-pig (Cohnheim), or in a 

 stellate manner in a series of finer branches, which again 

 form an exceedingly delicate superficially expanded web, 

 termed the subepithelial plexus (391). From this again fine 

 nerves run forwards at tolerably regular distances from each 

 other between the inferior vertically elongated cells and the 

 more superficially situated spheroidal cells of the epithelium. 

 In this course they run at right angles to the surface. On 

 arriving at the innermost layers of the superficial flattened 

 cells, they give off on all sides their finest terminal fibres, 

 which, after they have previously once or twice or repeatedly 

 divided, often terminate with somewhat swollen extremities in 

 the most superficial epithelial layers. 



Seen from the surface, the terminations of the fibres ascend- 

 ing through the epithelium correspond to the nodal points in 



