[ "5 ] 



the pupilla ; yet if we look into an human eye, or into that of 

 any animal, we will clearly fee that the iris. Co far from being 

 flat, is very convex, and that this convexity is greateft at its 

 fides. If befides viewing; clofely the eyes of living animals, we 

 examine through the cornea of inanimate ones, we will perceive 

 the fame appearance. Certain it is, that after cutting off the 

 cornea lucida. the fituation in which the eye is placed being 

 moftly on its pofterior extremity, makes the whole eye, and of 

 courfe the iris, appear flitter than they really are j but a little 

 refleflion, and an alteration in the pofiiion of the parts, will foon 

 prove the fallacy of this appearance ; for placing, the fides of the 

 eye nearly horizontal (according to their natural fituation) you 

 will quickly fee the iris afl'ume a much more convex appearance^ 

 provided in removing the cornea you have not injured the cryftal- 

 line capfula, even though the lofs of this cornea fliould have made 

 the parts lefs compad. 



Indeed, from the days of Galen, the convexity of the iris 

 was never doubted, 'till Vefalius firfl pretended to controvert this- 

 truth; and all the figures given of it by former anatomifts and 

 opticians have fo reprefented it, notwithftanding that they agreed 

 to place the cryftalline in the centre of the eye. But fince Monf, 

 Petel, (already quoted) has afiirmed that the iris is flit, and as 

 fuch has reprefented it, he has been in this error followed by 

 fubfequent writers : Yet that it is an error, and with refped to the- 

 operation of extraEiion^ a. very alarming one, will appear from the; 

 following exad defcription. 



Thb. 



