THE CORNEA. 827 



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

 numerous offsets by which they communicate with each other. Each contains a 

 cell, the corneal corpuscle, which resembles in form the space in which it is lodged, 

 but it does not entirely fill it. 



Immediately beneath the conjunct! val epithelium the cornea proper presents 

 certain characteristics 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 ought, therefore, to be regarded as a part of the proper tissue of the cornea. 1 



The posterior elastic lamina (membrane of Descemet or Demours], which covers 

 the proper structure of the cornea behind, presents no structure recognizable under 

 the microscope. It consists of an elastic, and perfectly transparent homogeneous 

 membrane, of extreme thinness, 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 tendency which it presents to curl up, or roll upon itself, with 

 the attached surface innermost, when separated 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 circular canal in the substance of the sclerotic 

 close to its junction with the cornea. This is the canal of Schlemm, or sinus 

 venosus sclerce ; it communicates internally with the anterior chamber through the 

 spaces of Fontana, and externally with the scleral veins. Some of the fibres of this 

 reticulated structure are continued into the front of the iris, forming the ligamentum 

 pectinatum iridis ; while others are connected with the fore part of the sclerotic 

 and choroid. 



The endothelial lining of the aqueous chamber covers the posterior surface of 

 the elastic lamina, is reflected on to the front of the iris, and also lines the spaces of 

 Fontana. It consists of a single layer of polygonal flattened transparent nucleated 

 cells, similar to those 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 

 number (Kolliker), forty to forty-five (Waldeyer and Siimisch) ; they are derived 

 from the ciliary nerves and enter the laminated tissue of the cornea. They 

 ramify throughout its substance in a delicate network, and their terminal fila- 

 ments form a firm and closer plexus on the surface of the cornea proper beneath 

 the epithelium. This is termed the subepithelial plexus, and from it fibrils are 

 given off w r hich ramify between the epithelial cells, forming a network which is 

 termed the intra-epithelial plexus. 



Dissection. In order to separate the sclerotic and cornea, so as to expose the second tunic, 

 the eyeball should be immersed in a small vessel of water and held between the finger and 

 thumb. The sclerotic is then carefully incised, in the equator of the globe, till the choroid is 

 exposed. One blade of a pair of probe-pointed scissors is now introduced through the opening 

 thus made, and the sclerotic divided around its entire circumference, and removed in separate 

 portions. The front segment being then drawn forward, the handle of the scalpel should be 

 pressed gently against it at its connection with the iris, and, these being separated, a quantity 



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." 



