70 



THE FUNDUS OCULI OF BIRDS 



white or light gray when directly illuminated 

 with the reflected light of the ophthalmo- 

 scopic mirror. 



The optic nerve-head gives one the visual 

 impression that it is formed of brilliant, 

 white, short, coarse, opaque fibres. Its 

 shape is unusual, being long and narrow, 

 with a rather striking resemblance to the 

 projecting, serrated jaws of the Sword Fish. 

 Extending along each side of the optic disc, 

 at right angles to it, are a few rather pale, 

 thin, opaque nerve fibres. 



The pecten is lighter brown in color than 

 usual, and is very narrow at its junction 

 with the papilla. On either side of it are a 

 few minute dots of brown pigment. The 

 inferior segment of the pecten forms a cor- 

 rugated, bulky mass which, however, ex- 

 tends well forward into the vitreous cavity 

 to the posterior surface of the lens. No 

 definite macular region was discovered in the 

 various specimens examined. 



Columbiformes 



Wonga Wonga Dove. Leucosarcia 

 picata. (Figs. 118 and 81 ; macroscopic views.) 

 The retina in the eyes of the one specimen 

 examined showed an unusually smooth 

 membrane. 



The long, narrow pecten resembles the 

 "comb" of the Wood Pigeon, and projects 

 into the vitreous like a house-heating radia- 

 tor with about 19 coils, forming 38 (or 

 more) convolutions in all. The ridge-like 

 crest conceals the upper middle line of the 

 pectinate mass which, in its turn, entirely 

 obscures a view of the optic entrance. The 

 lower free border of the marsupium appears 

 as a broad parallelogram covered with pig- 

 ment grains, contrasting sharply with the 

 superior end, which comes gradually to a 

 rounded point. 



There is no well-defined macular or foveal 

 area. 



As shown in Plate IX, page 129, the 

 ocular background of this species presents, 

 when examined by the ophthalmoscope, a 

 uniform, gray tint. White dots, lighting up 

 the fundus, are scattered over the entire field. 

 A few choroidal capillaries are to be seen. 



The optic disc forms a long oval; it ap- 

 pears as if it were composed of a collection 

 of white fibres, and these seem bunched to- 

 gether for about one-half the length of the 

 pecten. Opaque nerve fibres radiate from 

 the circumference of the papilla, while sev- 

 eral orange-red (choroidal) vessels, inter- 

 spersed with pigment dots, run on either side 

 of it. 



The pecten appears as an exceptionally 

 long, corrugated, dark-brown mass. Seen 

 through the mirror from above it has the 

 appearance of a piece of tarred rope. 



The macular area is seen to the inner 

 side of the disc and a little above its upper 

 end. The sheen of the pale-green reflex 

 that plays about it when illuminated by the 

 light of the ophthalmoscope looks like 

 watered silk. The fovea has the appearance 

 of a small green flare, something like that 

 from a bull's-eye lantern seen close at hand. 

 Only one macula can be seen. 



British Wood Pigeon. Columba palum- 

 bus. (Figs. 119 and 80; macroscopic views.) 

 The background of this species shows an 

 elongated, pointed, ovoid pecten, made up of 

 closely fitting plications (about 34 in number) 

 joined in a free upper margin. The main 

 body of the pecten is not concealed, as it 

 usually is, by the crest or line of junction 

 above, which has an abrupt flattened appear- 

 ance below, an acute sloping termination 

 above. 



A faint and doubtful foveal depression is 

 noticeable above and slightly to the nasal 

 side of the disc in some specimens examined 

 but this area does not show plainly in the 

 individual here pictured. 



The ophthalmoscopic appearances in this 

 species are depicted in Plate X, page 129. 



The general tint of the ocular back- 

 ground, as seen by the erect image, is pale 

 slate-gray. The eyeground is covered with 

 very small, dull-white dots so that the whole 

 fundus presents a lighter shade of gray 

 than it otherwise would. On the lower 

 half and each side of the optic disc are 

 seen several orange colored choroidal blood- 

 vessels, which become more numerous as one 

 approaches the periphery. Extending at 



