( 24,6 ) 



" In cliildrcn this aperture is more dilated than in 2;rown perfons ; 

 *' in elderly people it is flill fznaller than in adults, and has but little 

 *' motion ; hence it is, that thofc who begin to want fpectacles, are 

 " obliged to hold the candle between tlie eye and the paper they 

 ** read, that the ftrong light of the candle may force their rigid 

 " pupils into fuch a flate of contraftion, as will enable them to fee 

 *' di(tin(51:ly. Thofe who are fliort-fighted, have the pupils of their 

 *' eyes, in general, very large ; whereas in thofe whole eyes are 

 *' perfe6l, or long-fighted, they are much fmaller. 



" The whole of the choroidcs is opake, by which means no light 

 *' is allowed to enter into the eye, but what jjall'es through the pupil. 

 " To render this opacity more perfect, and the chamber of the eye 

 " flill darker, the pofterior furface of this membrane is covered all 

 " over with a black mucus, called the pigmentum nigrum. This pig- 

 *' ment is thinned upon the concave fide of the choroides, near the 

 '' retina, and on the fore fide of the iris; but is thickeft on the ex- 

 " terior fide of the choroides, and the inner fide of the uvea. 



" The circular edge of the choroides, at that part where it folds in- 

 " wards to form the uvea, feems to be of a different fubfiance from 

 " tlie reft of the membrane, being much harder, more denfe, and 

 *' of a white colour ; it has been called by fome writers the ciliary 

 " circle, becaufe the ligamentum ciliare (of which we (hall foon 

 " Ipeak) arifcs from it. 



" Retina. 

 " The third and lafi membrane of the eye is called the retina, be- 

 " caufe it is fpread like a net over the bottom of the eye ; others de- 

 " rive the name from the refemblance of the net which the gladia- 

 " tors called retiarii, employed to entangle their antagonifts. It is 

 *' the thinneft jmd Icafi; folid of the three coats, a fine cxpanfion of 



