II. 



TUNICA VASCULOSA. 

 BY PROF. A. IWANOFF. 



THE tunica vasculosa, or tunica uvea, lines the sclerotic, and 

 lies between it and the retina. At a distance of one millimeter 

 from the margin of the cornea it makes a sharp curve inwards 

 towards the axis of the eye, and rests on the anterior surface 

 of the lens, forming by means of this rectangularly bent part the 

 posterior wall of the anterior chamber of the eye. 



The posterior part of the tunica vasculosa, lining the sclerotic, 

 is termed the choroid ; whilst the anterior part, which appears 

 during life behind the transparent cornea, is named the iris, and 

 is perforated at its centre by an opening, the pupil. 



These two membranes are together named the tunica vasculosa, 

 because both are richly supplied with vessels, and because both sets 

 of vessels freely intercommunicate with one another. The other term 

 common to the choroid and iris, of tunica uvea, was conferred upon them 

 from their remote resemblance to the skin of a dark-coloured grape, in 

 which the hole for the pedicle corresponds to the pupil.* Many 

 anatomists now limit the term uvea to the layer of pigment that lines 

 the posterior surface of the iris. 



I. The choroid forms a thin vascular membrane, having a 

 thickness of 0'08 to 016 of a millimeter, which is firmly 

 attached to the sclerotic in two places, posteriorly at the point 

 of entrance of the optic nerve, where its inner layers are con- 

 tinuous with a ring that embraces the nerve, and from which 

 fine fibres are given off that penetrate the nerve itself ;f 



* Briicke, Anatomische Beschreibung des menschlichen Augapfds, p. 2, 

 1847. 



t H. Miiller, Anatomische Beitrage zur Ophthalmologie, Archiv ftir 

 Ophthalmologie, Band ii., Abtheilung ii., p. 24. 



