Lesson xxxvu/J THE EYE. 279 



And first, for a short description of the organ of 

 Sight, that noble instrument which 



O ' 



Takes in at once the landscape of the world, 



At a small inlet which a grain might close, 

 And half creates the woudrous world we see. 



YOUNG. 



The Eye is in form nearly globular: it consists 

 of three coats and -hree humours. The part of the 

 outward coat hid from our sight is called the Sole" 

 rotica : the front part, which rather projects out, 

 the Cornea : the next within this coat is that called 

 the Choroides, which serves, as it were, for a 

 lining to the- other; in the front it joins with that 

 part known by the name of the Iris, because it is 

 in different persons of different colours, as blue, 

 brown, green, &c. The iris is composed of two 

 sets of muscular fibres ; the one, of a circular form, 

 which contracts the hole in the middle called the 

 Pupi 1 , when the light would otherwise be too strong 

 for the E\e; and the other, of radial fibres, tend- 

 ing every where from the circumference of the iris 

 towards the middle of the pupil: these, by their 

 contraction, dilate and enlarge the pupil, when the 

 Irght is wi-ak, in order to admit more rays. The 

 third coat is only a fine expansion of the optic 

 nerve, which spreads like net work all over the in- 

 side of the~choroides, and is therefore called the 

 Retina : upon it are in a manner painted the images 

 of all visible objects, by the rays of light which 

 cither flow or are reflected from them. 



Immediately under the cornea is a fine transpa- 

 rent 



