302 TUNICA VASCULOSA, BY PROF. A. IWANOFF. 



of the development of the pigment layer from the external 

 lamella of the secondary eye vesicle, shows, however, that it 

 must be reckoned as belonging to the retina ; so that there 

 only remain four layers. But inasmuch as this division of 

 the choroid into four layers is not based on any facts of struc- 

 ture or position, we shall not adhere to it in the following 

 account. 



1. Vitreous membrane (Glashaut), (lamina vitrea of F. Arnold,* 

 elastic layer of Kolliker,t basal membrane of Henle,|) was origi- 

 nally described by Bruch, by whom it was named membrana 

 pigmenti. In the posterior segment of the choroid it forms a 

 very thin (0'0006 0'0008 of a millimeter) structureless, or 

 slightly fibrous (Kolliker) membrane, which, except by the 

 application of artificial means, is indissolubly connected with 

 the stroma of the choroid. The surface in contact with the 

 pigmented epithelium is perfectly smooth as far as to the ora 

 serrata. Solutions of potash and of sulphuric acid bring its 

 folds into view, because these reagents act differently on the 

 vitreous layer and the external layers of the choroid connected 

 with it. For since the protracted action of these reagents 

 causes a part of the stroma attached to the vitreous membrane 

 to break down ; so also, in concentrated acids and alkalies, it 

 frequently separates from the other layers of the choroid in the 

 form of isolated shreds. If the choroid be macerated for some 

 time in a ten-per-cent. solution of common salt, the fibrous 

 structure of the vitreous layer is very clearly brought into view. 

 Even then, however, it presents no trace of nuclei. The nuclei 

 described as existing in it by Bruch and Henle unquestionably 

 belong to the capillaries. 



In the anterior portion of the choroid the corpus ciliare 

 the characters of the vitreous layer undergo a marked change. 

 It here becomes paler, thicker, and is more amenable to the 

 action of alkalies and acids. It here also loses its smoothness, 

 its inner surface presenting microscopical elevations and de- 



* Anatomic, Band ii. , p. 1020. 

 f Handbuch der Gewebelehre, p. 661, 1867. 



$ Handbuch der Systematischen Anatomic des Menschen, Band ii., p. 620, 

 1866. 



Korniges pigment, 1844. 



