Eyelids and Lachrymal A pparatus of Birds. 
3 
ing at the outer and inner canthi, while other tufts are scattered 
over the lid surface. 
The inter palpebral space varies somewhat in the Sparrow; per- 
haps it is a little more circular and smaller when the bird accom- 
modates for near vision. The accompanying illustration gives an 
idea of the average relative size of the pupil and of the interspace 
during fixation for a near object. 
It will also be noticed that this space is entirely filled by the 
Sparrow’s cornea, a condition entirely unlike that in mammals. 
The space is 2.9 mm. wide and 4.5 mm. long. There is no 
lachrymal caruncle or anything to indicate it, nor would one expect 
it if the higher vertebrate caruncle be a vestigiary remains of the 
nictitating membrane. 
In the great majority of birds we, for obvious reasons, do not 
speak of an internal and external can thus but of anterior and 
posterior canthi. 
In Sparrow-like birds the pigment of the rounded, dark brown 
lid border does not extend beyond the point where it touches the 
eyeball, nor does it more than reach the palpebral derma. There is 
more pigment in the upper lid than in the lower. When closed, 
the junction of the two lids is well above the pupil, so that the 
cornea is fully protected. Probably there is no upward rotation of 
the eyeball in sleep. The lower lid follows the usual law in birds, 
of being the movable one. 
As a general proposition it may be stated that in respect of size, 
motility, etc., the lids in the Bird and Man are reversed, viz., the 
lower lid is the more important in Birds; the upper lid in human 
beings. The naked condition of both avian eyelids is not seen when 
the eye is open because they are then obscured by Ihe surrounding 
feathers. The external surface of each lid is quite thin, smooth, 
whitish-blue and devoid of feathers, except for a few solitary shafts. 
Very likely there is no interference with the luminous sense and 
light-direction sense when the Bird’s eye is closed. 
There is no differentiated tarsus in the upper lid, which is much 
shorter and thicker than the lower one, although the convoluted 
cylindrical margin of the upper lid is better shown in the upper 
than in the lower lid. 
Unlike Man and many other mammals, there is no true union of 
the conjunctivae of the two lids before the bird is born. In the 
Sparrow (probably in all the Passeriformes) the lids are wide opeu 
