224 FACULTIES OF BIRDS. 



the eye is spread over its inner angle, and when 

 any dust has fallen upon the ball, it sticks to this 

 and is carried into the corner of the eye by the 

 membrane folding back. In birds, again, this eye- 

 brush is much more extended, and is spread over 

 the whole eye by means of two muscles, one form- 

 ing a tendinous cylindrical canal, the other passing 

 through this and working like a cord in a pulley. 

 The membrane being translucent, when it is drawn 

 ove*- the eye like a curtain it is well calculated to 

 prevent it from being dazzled by too much light. It 

 is evidently, however, a mere conjecture that it is by 

 means of this membrane the eagle can look at the 

 sun ; for we do not see how it could be proved by 

 experiment, as it would be impossible to perceive 

 through it the direction of the pupil. Aristotle was 

 of opinion it was for the purpose of moistening the 

 eye ; but Aldrovand thinks we cannot well draw 

 such an inference, as our own eye is kept suffi- 

 ciently moist without such a provision. 



Willpughby describes the eye of the golden eagle 

 as having " a certain thick tunicle stretched forth 

 from below upward, covering the globe in nicta- 

 tion. Two eyelids, one above, the other beneath, 

 although the lower alone extending upward is suf- 

 ficient to cover the whole eye. The region of the 

 eyebrows is very eminent, like that prominent part 

 of houses called the eaves, under which the eyes 

 lie hidden, as it were, in a deep cavity. The eyes 

 are of a green colour (chlorops) of a fiery splendour, 

 shining forth in a pale blue. The pupil is of a 

 deep black. It is very admirable to observe what 

 care nature hath taken, and what provision she 

 hath made for the conservation of the eyes, than 

 which there is no part in this animal more excel- 

 lent ; for not being content with one tegument, as 

 is usual in other animals, she seemeth to have 

 framed four several lids or covers for them. The 

 membrane for nictation is the same thing, and af- 



