THE EYE. 389 



usually nothing left but the homogeneous matrix, the cells 

 having disappeared ; I noticed the latter, however, in many 

 instances, though rare and indistinct, particularly in those parts 

 of the organ bordering upon the lens and the hyaloid membrane 

 in general. From these observations I conclude that the 

 vitreous body, at an early period probably presents a sort of 

 structure most nearly approximated to embryonic cellular 

 tissue, but that subsequently all trace of such a structure is 

 normally lost, and it consists merely of a more or less con- 

 sistent mucus. 



Zonula Zinnii. — At the ora serrata, the hyaloid membrane 

 comes into intimate contact with the retina, and the latter 

 again with the choroid, so that it is extremely difficult to dis- 

 play the relations of the above-noticed zonula Zinnii. If this 

 part be exposed from the outside, some of the plgmentum 

 nigrum of the ciliary processes is almost always left adherent at 

 certain spots and often over a considerable extent. If the 

 places where this is not the case are examined, it is evident 

 that the outermost lamina of the zonula is a greyish layer, ex- 

 tending exactly so far as the processus ciliares are in connexion 

 with the zonula, and ceasing anteriorly in a slightly toothed, 

 irregular border. Under the microscope there are always 

 visible in this layer, even when the zone appears quite clear, 

 and particularly towards the front, a good many rows of pale 

 pigment-cells belonging to the choroid, which are situated prin- 

 cipally in the folds in which the processus ciliares were contained, 

 and give the entire zone a striped aspect. On the inner side 

 of this lies a single layer of clear, frequently very pale, poly- 

 gonal, nucleated cells, of 006 — Q'012"' in size, but which is 

 never entire, being always partially removed, together with the 

 ciliary processes, on which Henle and others have noticed it. 

 This layer of cells does not belong to the retina, as most 

 authors assume, and still less to the hyaloid membrane, but to 

 the choroid, and is nothing more than a stratum of cells not 

 containing pigment, lying immediately upon the corona ciliaris, 

 internally to the pigment (fig. 296 w, w) ; it does not, however, 

 in any way appear to be a distinct epithelial layer, but only the 

 uncoloured part of the pigmentary stratum, to which it would 

 stand in the same relation as the colourless epidermis-cells to 

 the coloured, in dark skins. This colourless epithelium of the 



