THE EYE. 353 



being intimately united and conjoined into larger, thinner or 

 thicker, flattened bands, which are disposed in the transverse 

 and longitudinal directions, alternating pretty regularly through 

 the entire thickness of the tunic and consequently, in vertical 

 sections, producing a lamellated structure. Truly independent 

 lamella, however, nowhere exist, the various longitudinal layers 

 having numerous points of connexion, as have also the trans- 

 verse laminae. However, on the external, but more particularly 

 on the internal surface of the sclerotic the longitudinal fibres 

 are collected into somewhat thicker plates, and thus acquire a 

 greater independence. 



Numerous fine elastic elements pervade the connective 

 tissue of the sclerotic, of the same form as those in the 

 tendons and ligaments (§ 80), viz. : as a network of the 

 finer or finest fibres, in which the sites of the original 

 formative cells are indicated by enlargements with nuclear 

 rudiments, so that the whole often very closely resembles 

 anastomosing, fusiform and stellate cells. During life, the ele- 

 ments of this network occasionally appear still to possess cavities 

 and fluid contents ; at any rate in portions of a dried sclerotic, 

 air is always to be seen in the bodies of all the cells (these 

 are the cretaceous corpuscles of Huschke), and consequently, 

 in this situation the opinion propounded by Yirchow, that chan- 

 nels of this kind are a sort of nutritive canals, would appear to 

 be completely justified, and the more so, because the vessels of 

 this tunic are at all events very scanty. They are derived 

 chiefly from the ciliary arteries and from those of the muscles of 

 the eye-ball, and constitute, as I and Briicke have found, a 

 tolerably wide-meshed network of capillaries of the last order. 

 Bochdalek has recently described nerves (and also Rahm, in the 

 Rabbit) in the sclerotic, but with Arnold and Huschke, I have 

 hitherto beenuuable to satisfy myself that these are anything more 

 than branches, on its inner side, running to the ciliary ligament. 



The cornea (fig. 296 C) is perfectly transparent, still more 

 compact and tough than the sclerotic, and is composed of three 

 special layers, viz.: 1. of the conjunctival membrane [conjunc- 

 tiva cornea); 2. of the proper cornea; and 3. of the membrane 

 of Descemet ; the first and last of which are formed of an 

 epithelium and a subjacent structureless membrane, and the 

 middle one of a fibrous tissue of a peculiar kind. 



ii. 23 



