346 THE VITREOUS HUMOUR, BY PROF. A. IWANOFF. 



surrounded by a special membrane, the so-called membrana 

 hyaloidea. This membrane is in reality identical with the 

 membrana limitans retinse. It is a constituent of the retina, 

 and is consequently applied immediately to the vitreous only 

 so far as the retina extends, that is, to the ora serrata. From 

 thence the membrana limitans is continuous with the pars 

 ciliaris retinae, but here meridianally running fibres lie between 

 the vitreous and the limitans, which are known under the 

 name of the zonula Zinnii, and these are intimately united 

 both with the limitans and with the vitreous. 



Near the ciliary processes the vitreous and the zonula 

 separate from one another, so that the whole anterior surface 

 of the vitreous which looks toward the canal of Petit and the 

 lens is not covered by any special membrane, nor by a pro- 

 longation of the limitans, as Henle maintains, nor by a special 

 membrana hyaloidea, as was formerly supposed. 



Henle* has demonstrated the non-existence of the hyaloidea. In 

 the meanwhile ' the name limitans hyaloidea is also not quite satis- 

 factory in a strictly anatomical sense. That the limitans is an integral 

 constituent of the retina is demonstrated in the clearest manner by 

 pathological processes taking place in the vitreous : in consequence of 

 which this last shrivels, and becomes detached from the retina.t In 

 such cases the membrana limitans always remains attached to the retina. 



In perfectly fresh specimens of the vitreous, and better still 

 in those that have been hardened, the peripheric part exhibits 

 distinct points of difference from the central. In the former a 

 more or less obvious laminated structure is perceptible, whilst 

 the latter appears to be homogeneous. 



Stilling termed the central part the nucleus, and the peri- 

 pheric the cortex. The homogeneous central portion, or nucleus, 

 does not occupy the centre of the mass, so as to be uniformly 

 invested by the concentric laminated cortex, but is pressed 

 forwards towards the lens in such a way that the cortical 

 substance becomes progressively thinner from behind forwards, 



* Eingeweidelehre, p. 661. 



t A. Iwanoff, Beitrage zur normal und pathologische Anatomic desAuges, 

 Archivfur Ophthalmologie, Band xv., Heft ii., p. 51. 



