280 THE TISSUES. 



have a homogeneous tissue like the perineurium, to which the pecu- 

 liar anastomosing pigment-cells, described on page 133, are added. 



7. Structure of the cornea. The true cornea is to be included his- 

 tologically under white fibrous tissue; though in chemical compo- 

 sition it is allied to cartilage, since it affords chondrine, and not 

 gelatine on boiling. 



The cornea considered as a whole, consists of five layers: 1, the 

 true lamellated cornea; 2, 3, the anterior and posterior elastic layers, 

 and 4, 5, the anterior (external), and posterior (internal) epithelium. 

 The anterior epithelium consists of three or four strata of cells, and 

 the posterior of one. The anterior and the posterior elastic layers 

 are merely basement-membranes underlying the epithelia. The 

 posterior is called the " membrane of Demours." The anterior is 

 bound to the lamellated cornea by fine elastic fibres, while the pos- 

 terior is not. The former is probably what remains of the vascular 

 conjunctiva covering the cornea of the foetus. 



But the true cornea (lamellated cornea, Todd and Bowman), con- 

 stitutes the greater part of the substance of this organ. This con- 

 sists of about sixty superimposed lamella, composed of transparent 

 fibres interwoven so as to leave tubular spaces 1 between them, and 

 is continuous with the white fibrous tissue of the sclerotica. These 

 tubular interspaces are arranged with tolerable regularity and con- 

 stricted at intervals, as shown by Fig. 178. This lamellated tissue 

 is the only portion of the cornea which is continuous with the 



Fig. 178. 



Tubes of the cornea proper, as shown in the eye of the ox, by mercurial injection. Slightly 



magnified. 



sclerotica, and its fibres appear similar to those of the latter, except 

 that they are transparent (Todd and Bowman). Their continuity is 



1 Kolliker, however, believes these tubes are artificial dilatations by injection 

 between the transparent fibres. 



