EYE OF THE ENGLISH SPARROW 355 



THE EYELIDS. 



The structures which protect the front of the eye of the spar- 

 row consist of three parts : the upper lid, lower lid, and the nicti- 

 tating membrane. 



The upper lid is short, thick, and almost immovable. The 

 lower lid is much longer, is thinner, and is capable of great 

 movement; in fact, the closure of the eye is due mainly to the 

 movement of the lower lid. When the lids are closed they meet 

 well above the pupil (figs. 2 and 9). 



The margin of the two lids is much thickened, very firm, and 

 has a horny appearance. These thickened edges are segmented 



Fig. 2 Enlarged semidiagrammatic drawing of the right eye of the sparrow 

 after death, showing the margins of the lids terminating in a thickened con- 

 voluted ring. A small tuft-like feather arises from the base of each of these 

 folds with the exception of a few at the anterior and posterior angles. 



into sausage-like portions of irregular size and shape. Figure 3, 

 representing the right eye of the sparrow drawn from life, shows 

 these marginal folds and the general external appearance of the 

 lids. These folds are more or less partially divided so that the 

 number is not constant; the upper lid has from 17 to 19 and the 

 lower lid about 18 divisions. Since the edges are firm and stiff, 

 it is readily seen that the function of these folds is to allow the 

 margins of the lids to bend so as to meet each other at all parts 

 when the eye is closed.' When the lids are completely closed 

 the junction does not form a straight line, but a slight curve 

 upward. 



