728 SPECIAL HISTOLOGY. 



that of its thickness. The correspondence of the corneal elements with 

 connective tissue is also shown by the following circumstances : 1, that 

 it is continuous at the border, by its elements, which in that situation 

 follow principally a radiating direction, directly and ivithout interruption 

 with the similarly disposed fibres of the sclerotic, so that there cannot 

 be the least question as to the non-existence of any natural demarcation 

 between the two tunics ; and 2, as Virchow was the first to show, that a 

 great number of anastomosing, fusiform and stellate, nucleated cells lie 

 among its bundles, just as they do in undeveloped elastic tissue (connec- 

 tive tissue-corpuscles of A^irchow), which also exist in the sclerotic, 

 though more branched. It can perhaps scarcely be doubted, that the 

 nutritive fluid, with which the cornea is constantly imbued in conside- 

 rable quantity, and which, in the large eyes of animals, may be directly 

 demonstrated by expression, is in great measure conveyed and distri- 

 buted in the interior, by the cells in question; a view which is only 

 strengthened by the knowledge that these cells, in morbid conditions of 

 the cornea, very frequently contain oil-drops, and occasionally, accord- 

 ing to Donders, even pigment, in their interior. The "corneal tubes" 

 injected by Bowman in the eye of the Ox and in that of Man must not 

 be confounded with this cellular network, and are probably to be ex- 

 plained as artificial dilatations of the minute interstices which normally 

 exist between the structural elements of the cornea, and which it is 

 thought may occasionally be perceived on microscopical examination. 



The conjimctival memhrane of the cornea (Fig. 296 a, h) is composed 

 principally of a soft, laminated epithelium, 0-023-0-050 of a line thick, 

 in which the deeper layers of cells are elongated and placed vertically 

 upon the cornea, whilst the middle ones are more of a rounded form, 

 and as they approach the surface, pass into a layer, 0'008-0"01 of a line 

 thick, corresponding to the horny layer of the epidermis, composed of 

 plates 0-01-0-14 of a line in size, though still nucleated and soft. Many 

 of these latter cells, as I have shown ("Zeitsch. f. wiss. Botanik," II., 

 p. 80), in consequence of their mutual pressure, present larger or smaller 

 pits, like certain cells in the urinary bladder, so as when viewed on the 

 side often to exhibit a stellate figure, which induced Valentin, who first 

 noticed this form, to regard them as cells with processes. Beneath the 

 epithelium, which, after death, is very soon rendered opaque by both 

 water and acetic acid, is a structureless lamella, first described by Bow- 

 man (anterior elastic lamella, of Bowman), 0-003-0'004 of a line thick, 

 which is especially evident in vertical sections and in folds of thin super- 

 ficial sections, upon the addition of alkalies, although it is by no means 

 so sharply defined from the true cornea as the membrane of Descemet, 

 nor does it seem to be of the same import as that membrane, but is per- 

 haps no more than the remainder of the vascular layer of the corneal 

 conjunctiva, which exists at an earlier period. Arched fibres, like rigid 



