4 FACULTIES OF BIRDS. 



short hairs, either to defend the eye with a grate-work 

 from any thing falling into it, or to perform some 

 unknown operation on light. The use of the eyelids 

 is strikingly demonstrated from what takes place when 

 they are cut off a savage punishment sometimes 

 practised in barbarous countries. This prevents 

 sleep, and from the constant irritation of the light, 

 the eyes inflame, the inflammation spreads to the 

 brain, and the victim of torture expires in the most 

 dreadful agony. 



Birds differ considerably from other animals with 

 respect to the eyelids, which are indeed formed hori- 

 zontally and very distinct ; but the under lid is in 

 most birds much larger and more moveable than the 

 upper, as was observed by Aristotle, in many cases 

 forming on the inner surface a smooth, polished plate 

 (lamina). 



The part, however, which we have more particu- , 

 larly alluded to, we may with some propriety call the 

 eye-brush (membrana nictitajts ; troisieme paupi- 

 ere, BLAINVILLE). In our own eye we may examine 

 this eye-brush at a looking-glass by turning the eye 

 away as far as possible from the nose. It is a little 

 red fleshy membrane, in form of a crescent, which in 

 such a position of 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 forming 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 over the eye like a curtain, it is well calculated 

 to prevent it from being dazzled by too much light. 

 * Petit, Mem. de PAcad. des Sciences, 1735-6. 



