120 



rendered uneven by small bodies dependent from 

 the iris. 



I have been told that there are similar bodies on 

 the lovi^er edge of the iris, but much more minute 

 in size. I have never observed them very distinctly 

 developed, but I by no means deny their existence. 



There is another variation between the horse's 

 and the human eye, of a very important and pecu- 

 liar character : at the inner angle of the eye, there 

 is found a dark membrane that, apparently at the 

 pleasure of the animal, is shot rapidly over the 

 eye, like a veil: it is instantly withdrawn, and 

 in its rapid transit, cleans the eye-ball of dust or 

 foreign particles that may have accidentally lodged 

 upon it. This membrane is called the haw : it is 

 not muscular, but its action is curiously explained ; 

 it is projected from its place by the compression, or 

 rather depression of the eye-ball into the socket, 

 occasioned by the retractor muscle. When the eye 

 is depressed by the play of this muscle, the elas- 

 ticity of the fatty substance behind the eye-ball 

 causes the haw to extend itself from the corner of 

 the eye, over the visible surface ; when the retractor 

 muscle ceases to act, the eye-ball resumes its usual 

 position, the fat returns to its place behind, and the 

 haw also returns to the socket from which it has 

 been momentarily pushed forward. 



