orrics. 2.31 



convex than the rest: this is called the cornea, 

 as CD. 



Immediately adherent to the sclerotica within, 

 is the choroides, which is a soft and tender coat, 

 composed of a multitude of vessels. This mem- 

 brane is inwardly of a russet-brown colour, almost 

 black. Like the sclerotica, it is distinguished into 

 two parts ; the fore-part being called the iris, while 

 the hinder-part retains the name of choroides. 

 The fore-part commences at the place where the 

 cornea begins : it here attaches itself more strongly 

 to the sclerotica by a cellular substance, forming a 

 kind of white narrow circular rim, called the ciliary 

 circle. The choroides separates at this place from 

 the sclerotica, changing its direction, turning, or 

 rather folding directly inwards towards the axis of 

 the eye, cutting the eye, as it were, transversely. 

 This part, called the iris, is composed of two kinds 

 of muscular fibres ; the one sort tending, like radii, 

 towards the centre of the circle, and the other 

 forming a number of concentric circles round the 

 same centre. The central part of the iris is per- 

 forated, and the orifice, which is called the pupil, 

 is varied in magnitude by the action of the two sets 

 of fibres composing the iris. When a very lumi- 

 nous object is viewed, the circular fibres contract, 

 and diminish the orifice ; and, on the other hand, 

 when the objects are dark and obscure, the radial 

 fibres of the iris contract, and enlarge the pupil so 

 as to admit a greater quantity of light. The iris is 

 differently coloured in different persons : in some it 

 is blue, in others brown, or of a hazel colour. 



The whole of the choroides is opaque, by which 

 means no light is allowed to enter into the eye, but 

 what passes through the pupil. To render this 

 opacity more perfect, and the chamber of the eye 



