14- 
pass the rods in number. We may assume, as one might expect, 
that the appreciation of color is excellent in all avian species. 
The extrinsic eye muscles in birds resemble those of the human 
eye, and, although the internal and external recti vary somewhat 
in their attachment to the globe, the purposes of these muscles are 
evidently the same in the avian as in the human eye. The pyramidal 
muscle that controls the nictitating membrane has not, so far as I 
know, an analogue in man. 
The refraction of birds' eyes is generally hypermetropic. I have 
examined quite a number of them by skiascopy and find, just as 
Lindsay Johnson discovered in mammals, that wild birds are in¬ 
variably far-sighted, while domesticated species tend to become 
short-sighted, astigmatic, or both, and to present evidences of intra¬ 
ocular disease. This was especially true of the large collection of 
owls in the London Zoological Gardens that I examined in the sum¬ 
mer of 1905 with the ophthalmoscope and skiascope. Those owls, 
it matters not what variety, that had lived in the gardens more than 
two years were generally less hyperopic than those recently intro¬ 
duced, while in the case of the former it was difficult to find rone 
that had not a more or less marked form of chorioiditis of the dis¬ 
seminate variety. 
Ophthalmoscopic appearances of birds' ocular fundi. Probably 
the chief reason why the interior of the eyes of birds has been so 
little studied during life is the difficulty inherent in the employ¬ 
ment of the ophthalmoscope and in reporting the results of the 
examination. As we are all well aware, the expert use of the in¬ 
strument, as practiced on the human subject, requires months of 
patient application before the student is able to distinguish the 
ordinary variations in the normal appearances of the uveal tract, 
retinal vessels, chorioid, optic entrance, vitreous, etc., while the 
usual pathological alterations in the tissues call for additional 
months of close observation. The same assertion can be made of 
animals' fundi and of birds' backgrounds in particular. In the case 
of the last-named animals care must be taken to prevent injury to 
delicate specimens during an ophthalmoscopic examination, and the 
observer must protect himself from bill and claw while the exami¬ 
nation goes on. I can assure any one who intends to pursue this 
study that the common barn owl, for example, can inflict severe 
