10 
Casey .4. Wood. 
The free margin of a portion posterior to it is set with pigment 
posed of delicate connective tissue interspersed with elastic fibres 
running in various directions.. It has a firm, thickened, free mar- 
gin, but no hyaline cartilage cells. This latter provision enables 
the free border to be closely applied to the cornea, so that when it 
sweeps over the latter it carries with it some of the fluid secretion 
of the Harderian gland and thoroughly cleans and moistens the 
corneal surface. The presence of elastic fibres gives to the third 
lid the qualities of a thin rubber band; when put upon the stretch 
it flies back instantly the moment the traction or “pull” is released. 
Fig. 4 — Enlarged Camera Drawings Showing the Marginal Plait of the 
Nictitating Membrane, Both Extended and Compressed. (.Wood and Slon- 
aker.) 
MP, Marginal plait; NE, epithelium of the nictitating membrane; CE, 
conjunctival epithelium; LE, lid epithelial lining. 
cells, but this marginal pigmentation is much less marked in the 
Sparrow than in other birds — the Snow Goose and Ostrich, for 
instance. A section of the third lid at right angles to the free 
border (see the illustration) shows the latter to be triangular in 
shape, like half an arrow-head, and to be thrown into folds both on 
its anterior and posterior surfaces. Interesting, also, are the basal 
folds of conjunctiva, somewhat like the folds of transmission of 
the human conjunctiva, disposed so as to aliow of considerable and 
rapid excursions of the membrane back and forth over the eyeball. 
