is needless to say, doing any good to his patient. The gland of 
Harder is also well developed in many mammals, and it, too, is 
occasionally mistaken for a diseased condition and summarily dealt 
with. A short time ago I saw a valuable bull-terrier from which 
the owner had, for cosmetic reasons, excised as much as was visible 
of these organs. The operation was followed by a large corneal 
ulcer and loss of sight in the affected eye. 
The Cornea of Birds. —Practically every bird has a cornea much 
more conical than that of the human species. This largely accounts 
for the brightness of avian eyes, and is one of the factors in their 
wonderful power and range of accommodation. 
The Avian Sclera. —The cone-like shape of the cornea is con¬ 
tinued into the sclerotic, which is entirely unlike the same structure 
in most of the other vertebrates. The anterior segment of the 
bird’s sclera is furnished with overlapping bony plates surrounded 
by connective tissue. These greatly strengthen the ocular walls, 
so that the marked pressure exerted upon them during accommoda¬ 
tive efforts do not permanently affect the shape of the eyeball. The 
posterior half of the bird’s eyeball is further strengthened by a cup 
of hyaline cartilage that extends to the bony plates in front. 
The Iris of Birds. —Even the most superficial observer can not 
walk through an aviary without remarking the brilliancy and 
extraordinary variety of coloration in the irides of birds. Zoolo¬ 
gists 2 have even built up a classification based upon variations in 
the color of the eyes in the genera of aves. The sphincter pupillce 
in birds is unusually well devloped, as are also the radial fibers. 
The Shape and Size of the Bird’s Pupil. —This should receive 
some comment, since it, as in man, is closely related to the focussing 
apparatus, and forms an important part of the peculiar uveal tract 
of birds. The motility of the iris and pupil is most remarkable. 
In watching the yellow-eyed parrot, for example, one can not help 
believing that the size of the pupil must he under the control of his 
will, so quickly does it expand and contract without apparently 
any relation to variations in the distance of the object fixed. In 
the majority of birds the pupils are round, but in some nocturnal 
birds, like the owl, these, round at one moment, may be contracted 
2 See, e. g., Th. Bruhin’s Die Iris der Vogel als iinterscliiedenes Merkmal der 
Arten, etc., in Zool. Garten, 1S70, p. 290. Also in Ibis, p. 207, 1859. On the 
Color of the Bird’s Iris. 
