HISTOLOGY OF THE VITREOUS HUMOUR. 347 



and at the ora serrata the several concentric layers are so 

 closely compressed together that the surface of the nucleus is 

 here separated from the limitans only by a very thin but 

 distinctly fibrous layer. The fibres of this layer run parallel 

 to the surface of the vitreous, forming wavy fasciculi bearing 

 some resemblance to the fibres of connective tissue. This 

 entire layer thus modified ultimately curves inwards towards 

 the optic axis, and covers the whole anterior surface of the 

 vitreous. 



Now, since we have here presented to us, not a single, but 

 several compressed layers, though these are only loosely con- 

 nected with each other, it is intelligible how easily we may 

 come to the conclusion that there is a special membrane 

 covering the vitreous and lying behind the lens, especially 

 since the most superficial of these layers is perfectly smooth. 

 The deeper-seated layers may sometimes in hardened eyes 

 be separated from each other, a circumstance that has led 

 Hannover and Finkbeiner* to the conclusion that the hyaloid 

 divides at the anterior surface of the vitreous into two laminae 

 in such a manner that behind the canal of Petit there is a 

 second canal, the canal of Hannover. 



In addition to the above-mentioned fibres resembling those 

 of connective tissue that are met with in the anterior part of 

 the vitreous, there are a considerable number of others like 

 elastic fibres. They commence as early as .at the sequator of 

 the eye, in the form of extremely fine looped fibres, but are 

 first seen in large numbers at the ora serrata; from this point, 

 lying in close apposition to the limitans, they curve round into 

 the pars ciliaris retinae, and here form the commencement of the 

 zonule of Zinn. A. canal of about two millimeters in diameter 

 runs forward through the vitreous from the papilla optica to 

 the posterior surface of the capsule of the lens. 



The difficulties that accompany the examination of the fresh vitreous 

 induced all the earlier anatomists, who paid particular attention to this 



* Vergleichende Untersuchungen der Starke des Glaskorpers bei den 

 Wirbelthieren, (Comparative researches on the density of the vitreous 

 humour in the Vertebrata,) Zeitschrift fur wssenschaft. Zoologie, Band vi., 

 p. 335. 



