THE SENSORIAL FUXCTIOX. 163 



biilliant carpet. It is the choroid coat itself which we see in tliem, and 

 not its covering ; and the red appearance is caused by the numerous blood- 

 vessels which are found on every part of that coat. 



^Vhen Ave have to treat of other domestic animals, we shall see how this 

 carpet is varied in coloui- to suit the situation and necessity of each. In the 

 ox it is of a dark green. He has not many enemies to fear, or much 

 difficulty in searching for nourishment, and the colour of the eye is adapted 

 to his food. In the cat and all his varieties it is yellow. We have heard 

 of the eyes of the lion appearing hke two flaming torches in the night. 

 There are few of our readers who have not seen the same singular glare 

 from the eyes of the domestic cat. In the wolf, and HkeAAase in the dog, 

 Avho, in his Avild state, prowls chiefly at night, it is grey. In the poor 

 unjustly-persecuted badger, who scarcely dares to crawl forth at night, 

 although sheltered by the thickest darkness, it is white ; and the ferret, 

 who is destined to hunt his prey through all its winding retreats, and 

 in Avhat would be to us absolute darkness, has no paint on the choroides. 



Tracing the choroides towards the fore part of the eye, we perceive that 

 it is reflected from the side to the edge of the lens, n, and has the appear- 

 ance of several plaits or folds. They are actually foldings of the membrane. 

 It is not diminished in size, but it has less space to cover, and there must 

 be duphcatures or plaits. They are usefully employed in the jDlace in 

 which Ave find them. They prevent the passage of any rajs of light on the 

 outside of the lens, and which, proceeding forAvard in various directions, 

 and uncondensed by the poAver of the lens, would render Adsion confused 

 or imperfect. These folds of the choroides are called the ciliary i^rocesses. 



Occupying the fore part of the eye, is the aqueous humour, q, so termed 

 from its resemblance to pure water. It is that by Avhich the cornea is pre- 

 served in its protuberant and rounded form. It extends to the crystalline 

 lens, g, and therefore a portion of it, although a very small one, is behind 

 the iris. Floating in this fluid is a membrane, with an oblong aperture, 

 called the Iris {m, p. 160). It is that Avhich giAcs colour to the eye. The 

 human eye is said to be black, or hazel, or blue, according to the colour of 

 this membrane or curtain ; and it is denominated the iiis, or rainboAV, 

 from its beautiful, intermingling hues. The colour A'aries little in the 

 horse, except that it always bears some analogy to that of the skin. We 

 rarely see it lighter than a hazel, or darker than a broAVTi. Horses per- 

 fectly Avhite, or cream-coloured, haA-e the iris Avhite and the pupil red. 

 When horses of other colours, and that are usually pied, have a white iris 

 and a black pupil, they are said to be icall-eycd. Vulgar opinion has 

 decided that a Avall-eyed horse is never subject to blindness, but this is 

 altogether erroneous. There is no diflerence of stmcture that can produce 

 this exemption ; but the Avall-eyed horse, from this singular and unpleasant 

 appearance, and his frequent Avant of breeding, may not be so much used 

 and exposed to many of the usual causes of inflammation. 



The aperture in the iris is termed the p^<j3i7, and through it light passes 

 to the inner chamber of the eye. The pupil is oblong, and variable in size. 

 It differs AAdth the intensity or degree of light that falls upon the eye. In 

 a dark stable the jiupil is expanded to admit a great proportion of the 

 light that falls upon the cornea ; but when the horse is brought toAvards 

 the door of the stable and more Hght is throAva upon the eye, the pupil 

 contracts in order to keep out that extra quantity Avhich would be painful 

 to the animal, and injurious to vision. When opposed directly to the sun, 

 the aperture A\dll almost close. 



This alteration of form in the pupil is efiected by the muscular fibres 

 that enter into the composition of the iris. There are tAvo orders of these 

 fibres, the circular and the straight or radiating. "Wlien the circular fibres 



M 2 



