HISTOLOGY OF THE VITREOUS HUMOUR. 351 



extend over the surface of the vitreous, a few penetrate into its interior, 

 where they are soon ( lost. 



According to the same author, the superficial fibrous tissue of the 

 limitans hyaloidea divides at the point where the orbicularis ciliaris 

 begins to enlarge into the corpus ciliare, into two laminae, of which 

 one passes inwards to form the hyaloidea of the shallow groove, 

 whilst the other passes outwards to the pars ciliaris retinae, in order to 

 form the zonula. 



The researches above given show, in opposition to those of Henle, 

 that all those changes to which the limitans is subjected, take place 

 in the peripheric layers of the vitreous, whilst the limitans itself 

 remains unaltered, and becoming progressively thinner, passes simply 

 from the ora serrata to the pars ciliaris retina. It thus not only 

 takes no part in the formation of the urceolate groove of the hya- 

 loidea, which, as has been above shown, does not exist, but the part 

 it takes in the formation of the zonula is more than doubtful. I at 

 least have never been able to discover this relation, whilst the origin 

 of the zonula from the vitreous may be very easily observed. 



It only remains therefore to determine whether the limitans is 

 actually continuous with the pars ciliaris retinas. Henle himself 

 admits that if we consider the fibrous layer of the zonula as the an- 

 terior lamina of the limitans, the latter again splits into two layers at 

 the apices of the ciliary processes, and that in some cases he has even 

 seen the hyaloid membrane extend beyond the origin of the fibres of 

 the zonula on the orbiculus ciliaris, 



As regards the development of the zonula, we now know that it 

 does not exist in the embryo, so long as the vessels investing the 

 capsule are present, although at this period the limitans is already 

 completely developed. The zonula first appears at the time when 

 the capsular vessels atrophy, and as their atrophy proceeds becomes 

 progressively more and more distinct. 



But if the limitans passes unaltered from the ora serrata over the 

 pars ciliaris retinas, it is self-evident that it cannot possibly form a 

 quantity of fibres of the zonula, and beyond this, by further division, 

 the membrane of the quoit-like groove. 



All this confusion originates in the fact being overlooked, that the 

 superficial layers of the vitreous become already altered in their 

 structure in front of the ora serrata, and are intimately fused with 

 the limitans and the retina. At the same time the coalesced parts 

 are not altogether inseparable since, in some pathological cases, and 

 even in healthy eyes, treatment with alkalies will very often effect 



