250 orncs. 



for it to rest upon, and facilitate its various move- 

 ments. 



The eye-brows defend the eye from the light 

 when it is too strong, and prevent their being in- 

 commoded by any substances that might slide 

 down the forehead, and thence fall into the eyes. 



The eye-lids, like two substantial curtains, pro- 

 tect and cover the eyes when we are asleep ; when 

 we are awake, they diffuse by their motion, and by 

 peculiar secreting organs, a fluid over the eye, 

 which cleans and polishes it, and thus renders it 

 fitter for transmitting the rays of light. 



That the eye-lids may shut with greater exact- 

 ness, and not fall into wrinkles when they are ele- 

 vated or depressed, each edge is stiffened by a 

 cartilaginous arch. The eye-lashes, like two palli- 

 sades of short hair, proceed from these cartilagi- 

 nous edges, warning the eye of danger, protecting 

 it from straggling motes, and warding off the wan- 

 dering fly. 



The eye itself is of a globular form, but more 

 protuberant on the fore-part than behind. 



It is composed of three coats, or teguments, one 

 covering the other, and inclosing three different 

 substances, called humours. 



ABCD (Plate 13. fig. 4.) is a section of the 

 globe of the eye, the three concentric circles re- 

 presenting the three coats. 



The external coat, or membrane, is called the 

 sclerotica; it is strong, elastic, and of a white 

 colour, resembling parchment : the hinder part is 

 very thick and opaque, but it grows gradually 

 thinner, as it advances towards the part where the 

 white of the eye terminates. A circular portion 

 of it in front is perfectly transparent, and more 



