THE EYE. 183 



more highly vascular ; does receive red blood, and forms a 

 secreting surface to defend these parts from the irritation 

 of the tears. 



The sclerotica {Fig 19 . 7) is the outermost of the more 

 complete investments of the globe ; and is likewise the 

 thickest and strongest ; forming all the posterior and larger 

 part of the globe ; the smaller and the more forward por- 

 tion of the sphere consisting of the cornea. The cornea 

 {Fig 19 . 6) , as part of a tunic, it extends over the anterior 

 portion of the bulb of the eye ; being distinct from that 

 portion of which the larger and posterior part of the globe 

 is composed. The cornea, in fact, is that transparent por- 

 tion which the spectator looks through when he observes 

 the eye of a living horse. The convexity varies much in 

 different subjects ; by which the focal distance is adapted to 

 the viewing of near or more distant objects. In man, the 

 focal distance of the eye is less than a foot ; thus his 

 cornea is considerably more convex. But the horse has to 

 see objects from the ground ; in him, therefore, the con- 

 vexity is less, and the focal distance of his eye is probably 

 some feet. The cornea in every animal is organized ; not 

 highly sensitive ; but capable of repairing injuries of a size 

 and importance almost exceeding belief. Its reparative 

 powers are very active ; and though less organized than 

 most parts, yet in the speed of restoration it comparatively 

 exceeds all others. 



The iris. — This moveable curtain is situated within the 

 eye, near to the cornea ; to which it corresponds in outward 

 shape, being attached to the ciliary ligament, that helps to 

 unite the cornea to the sclerotica. The colour of the eye 

 depends on the iris ; being wholly governed by a black pig- 

 ment, secreted at the back of the iris, and called the uvea : 

 the office of this pigment is to absorb all rays of light 

 turned upon it. Wall-eyed horses have none of this pig- 

 ment ; therefore their vision must be deficient ; the human 

 eye is commonly grey, black, or blue : in the horse it is 

 usually brown ; from the deep colour of the pigment being 

 partially visible through the iris. The space between the 

 inner circumference of the iris is usually termed the pupil ; 

 the size of which necessarily increases or decreases as the 



