20 INNERVATION. [ciIAP.XVIl. 



bited by a section however thin, immersed in water, and deranged 

 by stretching. 



Of the Anterior Elastic Lamina. This is a transparent, homo- 

 geneous lamina, co-extensive with the front of the cornea, and form- 

 ing the anterior boundary of the cornea proper. It is a peculiar 

 tissue, the office of which seems to be that of maintaining the exact 

 curvature of the front of the cornea ; for there pass from all parts of 

 its posterior surface, and in particular from its edge, into the sub- 

 stance of the cornea proper and sclerotic, a multitude of filamentous 

 cords, which take hold, in a very beautiful artificial manner, of the 

 fibres and membranes of those parts, and serve to brace them and hold 

 them in their right configuration (fig. Ill, 6). These cords, like the 

 elastic lamina of which they are productions, appear to be allied to 

 the yellow element of the areolar tissue. They are unaffected by 

 the acids. The anterior elastic lamina sustains the conjunctival epi- 

 thelium which covers the cornea, and is very probably the represen- 

 tative of the basement membrane of the mucous system, as it 

 occupies the corresponding position in regard to the epithelium. 

 Its thickness is about -jcW f an i ncn - 



The conjunctival epithelium of the cornea may always be obtained 

 from a fresh eye, by gently scraping its surface. It consists of three 

 or four layers of superposed particles, inclining to the columnar form 

 where they rest on the anterior elastic lamina, and becoming imbrica- 

 ted scales on the surface (fig. 1 1 1 , a). In many of the larger animals 

 this epithelium consists of a much deeper series of nucleated parti- 

 cles, and its transparency then becomes a remarkable character. 



It is in this epithelium that particles driven with force against 

 the eye generally lodge, and it is easily detached by the instrument 

 used to extract them. Vessels shooting into the cornea in disease 

 lie under it, and small ulcers are formed by its destruction. In 

 animals which cast their skin this lamina is shed with the cuticle 

 of the body. 



The posterior elastic lamina of the cornea (fig. 1 1 1, d) is a very thin 

 membrane in which no structure can be detected. It has all the 

 transparency of glass, and does not become opaque by maceration, 

 boiling, or the action of acids. It adheres but slightly to the cornea 

 proper, and, when peeled off, it has such a tendency to curl with 

 its anterior surface inwards, that it is difficult to retain a piece 

 of it in an extended form. If floated in water, it exhibits a 

 peculiar glistening lustre resulting from its density. It readily 

 tears, yet is so hard that it is bitten through with difficulty. 

 Its elasticity is great, and has been supposed to contribute to 



