452 



SLONAKER. 



[Vol. XIII. 



Fig. 4. — Chickadee (Parus atricapillus) 3/1. 

 f Fovea. p Pecten. GH and GI Axes of vision. 



may be greater or less during life. The pecten, /, marks the 

 entrance of the optic nerve. When a second fovea is present 

 it is situated on the temporal side of the nerve entrance, as 

 shown in Fig. 5. 



In order to show the relation of the retinal arteries to the 

 area and fovea centralis, they were injected with the gelatine- 

 carmine mass of Ranvier. In small animals this injection was 

 made in the carotid arteries, while with large animals the eyes 

 were removed and the injection made into that branch of the 

 ophthalmic artery which supplies the retina. After injection 

 the eye was at once cooled and hardened in alcohol. When 

 hardened, the front half of the globe and the vitreous humor 

 were carefully removed, exposing to view the retina, arteries, 

 entrance of nerve, and area and fovea centralis, when present. 

 Usually the fovea is readily seen if it is present, but the area 

 is sometimes very difficult to discern, and were it not for the 

 blood-vessels acting as landmarks, it might be overlooked 

 altogether. Drawings were made of the posterior half, great 

 care being taken to orient it so that one would look into it 



