SECT. 228.] ZONULE OF ZINN. 573 



then terminates anteriorly with a slightly-toothed, irregular border. 

 In the anterior portions especially, we may always recognise with 

 the microscope, even when the zone looks quite clear, a consider- 

 able number of pale pigment cells of the choroid, arranged in 

 rows, and situated more especially in the folds which contained the 

 ciliary processes ; they give the whole of this grey layer a striated 

 appearance. Next, internally, lies a simple layer of clear, often 

 very pale, nucleated cells, polygonal or cylindrical, and measuring 

 0006'" to 0012'". This layer, however, is never complete, but 

 always becomes partially detached, along with the ciliary processes 

 and cells, from it, as had already been observed here by Ilenle and 

 others. This layer of cells belongs to the retina, and not to the 

 hyaloid membrane, and is most fitly designated by the name pars 

 ciliaris retinal. It is the immediate continuation of the retina, 

 though it contains none of the essential parts of this membrane, 

 and its connection with it is probably only owing to the circum- 

 stance, that its rudiment in the foetus is common to it and to the 

 retina; it passes forwards between the corona ciliaris and the 

 zonule of Zinn, is intimately connected with both, and, leaving 

 the zonule of Zinn, terminates where the ciliary processes border 

 upon the iris. 



Apart from these layers, the zonula is a thin, transparent, but 

 pretty firm membrane, which extends from the ora serrata retince 

 to the border of the lens, and appears as the continuation of the 

 hyaloid membrane. It consists of peculiar pale fibres, well de- 

 scribed by Henle, which resemble certain forms of reticulate con- 

 nective tissue, except that they are more rigid, generally present 

 no distinct fibrilloe, and become less swollen in acetic acid. These 

 fibres are very fine, resembling in part the fibrils of connective 

 tissue, at the point of their origin at the outer side of the hyaloid 

 membrane; they are here, however, somewhat behind the ora 

 serrata retina?, but in most intimate connection with the hyaloid ; 

 they then run forwards, forming a layer which is at first loose, but 

 afterwards becomes denser and denser, increasing in thickness up 

 to croo4'" or even croi"' and more, with frequent divisions and 

 anastomoses. The fibres and their divisions run, for the most part, 

 parallel to each other, till, at the free part of the zonula, they form 

 a perfectly connected layer (the individual bundles being always 

 separable, however), and then coalesce with the capsule of the lens. 

 From the ora serrata to the commencement of Petit's canal, a 

 hyaloid membrane is no longer distinguishable with the zonular 

 fibres; on the other hand, at the above-mentioned canal, where 



