756 SPECIAL HISTOLOGY. 



vitreous body of the adult, of the previous conditions there was usually 

 nothing left but the homogeneous matrix^ the cells having disappeared; 

 I noticed the latter, however, in many instances, though rare and indis- 

 tinct, particularly in those parts of the organ bordering upon the lens 

 and the hyaloid membrane in general. From these observations I con- 

 clude 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 consistent mucus. 



Zonula Zinnii. — At the ova serratcr, the hyaloid membrane comes 

 into intimate contact with the retina, and the latter again with the 

 clioroid, so that it is extremely difficult to display the relations of the 

 above-noticed zonula Zimiii. If this part be exposed from the outside, 

 some of the pigmentum 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 grayish layer, extending exactly 

 so far as the lyrocessus ciliares are in connection 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 pigrnent-cells belonging to the clioroid, which are situated 

 principally in the folds in which the jn'ocessus 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, polygonal, nucleated 

 cells, of 0*006-0*012 of a line 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 oorona 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 uncolored 

 part of the pigmentary stratum, to which it would stand in the same 

 relation as the colorless epidermis-cells to the colored, in dark skins. 

 This colorless epithelium of the corona ciliaris, as I shall term these 

 cells, is most distinctly shown on the ciliaiy processes, as a clear border 

 sharply defined on the inner side, and often 0-006-0-008 of a line broad, 

 whose large, frequently shortly cylindrical cells, may usually be recog- 

 nized without any trouble, and are always rendered distinct by acetic 

 acid ; whence it is evident that the boundary is composed only of them, 

 and is not a special membrane. Posteriorly, this cellular stratum 

 reaches as far as the ova serrata, extending anteriorly to the termina- 

 tion of the ciliary processes (Fig. 296 iv'), and on either side it is con- 



