316 NATURAL THEOLOGY. 



stant that the eyelids are closed, the eyeball 

 makes a movement which raises the cornea under 

 the upper eyelid. 



If we fix one eye upon an object, and close the 

 other eye with the finger, so as to feel the con- 

 vexity of the cornea through the eyelid, we shall 

 perceive when we shut the eye that is open, that 

 the cornea of the other eye is instantly elevated ; 

 and that it thus rises and falls in sympathy with 

 the eye that is closed and opened. This change 

 of the position of the eyeball takes place during 

 the most rapid winking motions of the eyelids. 

 When a dog was deprived of the power of closing 

 the eyelids of one eye by cutting across the nerve 

 of the eyelids, the eye did not cease to turn up 

 when he was threatened, and when he winked 

 with the eyelids of the other side. 



Nearly the same thing I observed in a girl 

 whose eyelids were attached to the surrounding 

 skin, owing to a burn ; for the fore part of the 

 eyeball being completely uncovered, when she 

 would have winked, instead of the eyelids descend- 

 ing, the eyeballs were turned up, and the cornea 

 was moistened by coming in contact with the 

 mouths of the lachrymal ducts. 



The purpose of this rapid insensible 'motion of 

 the eyeball will be understood by observing the 

 form of the eyehds and the place of the lachrymal 

 gland. The margins of the eyelids are flat, and 

 when they meet, they touch only at their outer 

 edges, so that when closed there is a gutter left 



