THE EYE. 727 



the transverse and longitudinal directions, alternating pretty regularly 

 through the entire thickness of the tunic, and consequently in vertical 

 sections, producing a larnellated structure. Truly independent lamella, 

 however, nowhere exist, the various longitudinal layers having numerous 

 points of connection, as have also the transverse lamince. 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 rudi- 

 ments, so that the whole often very closely resembles anastomosing, fusi- 

 form, and stellate cells. During life, the elements of this network occa- 

 sionally 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 con- 

 sequently, in this situation the opinion propounded by Virchow, that 

 channels 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 eyeball, and constitute, 

 as I and Brucke have found, a tolerably wide-meshed network of capil- 

 laries 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 been unable to satisfy myself that these are anything 

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



The cornea (Fig. 296 (7) is perfectly transparent, still more compact 

 and tough than the sclerotic, and is composed of three special layers, 

 viz. : 1, of the conjunctival membrane (conjunctiva cornece) ; 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 mem- 

 brane, and the middle one of a fibrous tissue of a peculiar kind. 



The proper cornea, or the fibrous layer (Fig. 296 c), by far the most 

 important part of the whole tunic, consists df a fibrous substance closely 

 allied to connective tissue, but which, according to J. Muller, affords 

 when boiled, riot gelatin, but chondrin. Its elements, pale bundles, 

 0*002-0*004: of a line in diameter, in which, at least when teased out, 

 finer fibrils are usually perceptible, sometimes more and sometimes less 

 distinctly, are united into flat bundles. These bundles, which have their 

 flat sides always parallel with the surface of the cornea, decussate in 

 various directions, and exhibit, if not complete lamellce, yet a distinctly 

 laminated structure, owing to which the cornea is very readily torn and 

 penetrated in the direction of its surfaces, and with great difficulty in 



