42 LESSONS IN HORSE JUDGINa. 



two structures is the ^ iris/ which acts hke a cur- 

 tain to a window, and is really the curtain of the 

 eye. It is a very dehcate moving muscle, flat- 

 tened Hke a sheet of paper and ovoid, having an 

 ovoid hole in its very centre (Fig. 5, A 5), wliich, 

 as we have seen, is the ' pupil ' of the eye through 

 which the light passes. Now this hole, or pupil, 

 varies much in size. When the eye is exposed to 

 a bright light it becomes very small, but in the 

 dark it enlarges to its widest; This is well seen 

 in ourselves, but better seen in the cat. Put a 

 cat before a window and you find the pupil 

 diminishmg almost to the size of a pin point. 

 Then this muscle acts by enlarging or diminish- 

 ing the 'pupil.' It does so in this way: Fig. 5, 

 Ay 2, represents the iris as viewed from behind. 

 It is seen to be made up of inner circular fibres 

 which radiate from these. When the pupil les- 

 sens, it is by the circular fibres contracting, but 

 when it widens it is by the radiating fibres con- 

 tracting. What we have to do in the darkened 

 stable is to see that the 'pupil' diminishes and 

 enlarges freely. For this purpose we cover the 

 eye with our hand to darken it for half a minute 

 or so when we expect the 'pupil' will dilate; 

 then we place the candle close to the back of the 

 hand that is covering the eye and suddenly re- 

 move the hand and watch the pupil contract, 

 which it ought to do from the glare of the light 

 being too much for the eye. In a darkened 

 stable, and a candle held away from the eye, you 

 will still see the pupil widenhig and narrowing, 

 which is, of course, a sign that it is in good order 



