IS AN ESSAY ON 



anatomists not to have place. For Varolius* 

 long ago observed, that the crystalline is not 

 situated in the middle of the eye, but more in- 

 wardly ; and the accurate Zinnt has more lately 

 mentioned, that if the eye be divided into a 

 right and left half, the centre of the crystalline 

 will be found in the inner portion. HallerJ 

 confirms this fact ; and Winslow's || observation, 

 that the centres of the pupil and iris do not 

 coincide, but that the former is 'nearer to the 

 nose than the latter, is connected with it ; since 

 both Zinn and Haller agree, that the centre of 

 the pupil is placed in the axis of the crystalline, 

 while that of the iris is evidently in the common 

 axis of the cornea and globe. Now, a conse- 

 quence of this position of the crystalline is, that, 

 contrary to what I believe is universally main- 

 tained, no ray of light whatsoever can pass un- 

 bent to the retina from the atmosphere, or any 

 other medium differing in refractive power from 

 the aqueous humour. If, then, the line joining 

 the centres of the cornea and globe of the eye 

 be what is called the optic axis, and if it be 

 true, that objects appear single when we direct 



* Varolii Anatomia, 12mo. p. 16. 



f De Oculo, 4to. p. 127. 



+ Elementa Physiologiae, tozn. v. p. 403. 



J| Winslow's Anatomy, vol. ii. p. 379, English edition* 8vo. 



