blood- ressels, but so fine, as not to hinder the smaU 

 )est rays of light. It has an exquisite sense, that oa 

 the least touch of any thing, the tears may be expres- 

 sed, to wash off any filth, which by adhering to it 

 jaight render it dim or cloudy. The rest of the scle- 

 rotica is opaque, and of the same colour with the 

 dura mater. 



The second coat is called the uvca. It is much 

 thinner than the former, though thicker than the pia 

 mater from which it proceeds. In the forepart of it 

 Is a round hole, which with the chrystalline humour 

 interposed, constitutes the pupil, surrounded by the 

 iris, so named, from its supposed resemblance to the 

 colours of the rainbow. The thirJ and inmost coat 

 is termed the retina. It is extremely thin and soft, 

 and darker-coloured than the lower part of the optic 

 nerve, of which it is a continuation. 



** If it be questioned, says Dr. Haller, whether 

 the object is painted upon the retina, or upon the 

 choroides; we answer, this late supposition is incon- 

 sistent with known observation, by which the retina 

 IB evidently a most sensible expansion of the nerve, 

 while the choroides has only a few nerves, with smali 

 vessels which are certainly blind. It is also opposed 

 by the great variety of the choroides in different ani- 

 mals, while the constant uniformity of the retina is 

 equally remarkable, to which add the black membrane 

 that is interposed betwixt the retina, and choroides, 

 in some kinds of fish. Finally, anatomy demonstrates 

 that the choroides is seated in the blind part of the 

 eye, but is itself of a white colour," 



25, The Aqueous humour,resembling the colour and 

 consistence of water, lies in the fore part of the 

 eye, just behind the cornea : its interior surface is 

 con-vex ; the other, a little concave. Whence this 

 humour is derived we cannot tell ; but its source must 

 be plentiful, for if the coat containing it be so wound* 

 cd, that all the humour runs out, it needs only to keep 



