IN SEARCH OF A HORSE. 131 



retina. This last-named membrane is an expansion 

 of the optic nerve over every portion of the interior 

 surface of the choroides, till it arrives at the edge of 

 the crystalline lens. 



The cornea is formed by the first membrane, the 

 conjunctiva : it is the transparent convex substance 

 that forms, as it were, the outward case for the pupil 

 and iris. 



The anterior chamber of the eye, being the cavity 

 between the cornea and the iris, and the posterior 

 chamber, which extends from the iris inwardly to 

 a reflection of the choroides, called the uvea, are 

 both occupied by a transparent fluid named the 

 aqueous humor. 



The crystalline lens is also a firm but transparent 

 humor of a convex form; it is contained in a very 

 delicate membrane, called the capsula, and is imbed- 

 ded in the vitreous humor — a very fine transparent 

 fluid, filling the whole cavity of the globe, behind 

 the lens. 



Externally, the eye-ball and the cornea are lubri- 

 cated by the tears. 



There is some difl*erence in the construction of 

 the human eye and that organ in the horse ; the 



