208 MANUAL OF MODERN FARRIERY. 



part of the eye, from the optic-nerve to the cornea. This 

 is intended to absorb the stray rays of light which miglit 

 dazzle and confuse the animal, and is not found on any 

 portion which may be called the field of vision ; but in its 

 stead a bright green substance is spread, which extends more 

 over the upper than the lower portion, because the objects 

 which are most necessary for him to see are below the level 

 of the head. This in some way, yet undiscovered, enables 

 the animal to see even when it is comparatively dark. In 

 the dusk this beautiful sea-green colour may be seen in 

 the eye of a horse. 



Cream-coloured, or perfectly white horses, have not thi3 

 dark pigment ; so that the ordinary appearance of tho 

 pupil is red instead of black. In looking into their eyes 

 we do not see the coverinG^, but the choroid coat itself. 



7n, m. The nis, or rainbow-coloured circular membrane, situated 

 under the cornea in front of the eye, and on which the 

 colour of the eye depends. The dupUcature behind is the 

 uvea, so called from its colour resembling a grape. See also 

 plate iii. fig. 5, i The iris acts as a curtain, and floats in 

 the aqueous humour. 



In horses the colour of the iris is subject to little variation, 

 but for the most part has some analogy with that of the 

 hide, varying in different degrees from hazel to dark brown. 



n. The pupil is placed in the centre of the cornea, and through 

 which all the rays of objects pass to the retina or mirror of 

 the eye. See also plate iii, fig. o, k. 



In the horse it is of an oblong form, (see plate iii. fig. 4.) 

 It is variable in size, depending upon the intensity of the light 

 in which it is viewed. In the open air it will be niuch con- 

 tracted, so as to prevent too large a quantity of light being 

 thrown upon the retina, as it is painful and injurious to that 

 object to receive too great a portion of it, as well as pre- 



