172 OKGANS OF SENSE. 



the conjunctiva, which is distinguishable from it by 

 the greater looseness of its texture, and by the larger 

 number of plasmatic cells which it contains (PL 

 XXVIII. fig. II.). Its deep surface is closely attached 

 to the dioroid membrane only at its anterior limits, 

 where it gives insertion to the ciliary muscle (fig. 

 IV. 1). The canal of Schlemm is also found along 

 the line which limits the sclerotica in front, forming 

 a tunnel near the deep surface of the membrane (fig. 

 IV. 2). 



The cornea is composed of an amorphous funda- 

 mental substance, which contains a great quantity of 

 plasmatic cells (fig. I. 2 ; fig. III. 2). These are dis- 

 posed very regularly in concentric lines running 

 parallel with the two surfaces of the cornea. When 

 very dilute acetic acid is applied to prepared speci- 

 mens of the cornea, the stellate shape of these cells, 

 and the numerous anastomoses between their prolon- 

 gations, are rendered perfectly visible, and their 

 appearance recalls vividly the structure of bone. 

 But if the acid should be too much concentrated the 

 prolongations of the cells become pale, and their 

 bodies alone remain visible (PL II. fig. V.). The 

 front surface of the cornea is limited by a thin edge 

 which, in a section, forms an amorphous border from 

 aloth to aioth of a line in thickness, the anterior mar- 

 gin being in contact with the epithelium of the con- 

 junctiva (PL XXVIII. fig. II. 3). Its posterior sur- 

 face also forms an amorphous border, of the same 

 thickness as the latter ; it is continuous, by means of 

 fibrous tissue, with the anterior margin of the scle- 

 rotica and the ciliary muscle (fig. III. 4 ; fig. IV.). 



