THE FUNDUS APPEARANCES IN VARIOUS ORDERS OF BIRDS 



101 



region. Figure 135 furnishes an enlarged 

 picture of this area, which is a duplicate of 

 the area nasalis except that the fovea is 

 shallower and not so black, while the pigmen- 

 tation of the surrounding ring is less marked. 

 The pecten has 32 convolutions — 16 on 

 each side — united to a long, narrow sinuous 

 crest. The fold that constitutes the front of 

 the free border becomes broader and rounded 

 as it gradually slopes from the crest to the 

 superior end of the optic disc. Uncertain 

 glimpses are gained of the papillary borders 

 through a few spaces between the more cen- 

 tral pectinate folds; otherwise the surface of 

 the optic entrance is entirely obscured. 



Cuculiformes 



Yellow-billed Cuckoo. Coccyzus ameri- 

 canus. (Figs. 102 and 136; macroscopic view.) 



The single macular region is of immense 

 size — considerably larger than the untinted 

 area on the nasal side of the pecten, and 

 two-thirds as wide as the optic entrance is 

 long. A nebulous zone of pigment dots 

 encloses this large sensitive area, the dots 

 being drawn as distributed everywhere ex- 

 cept at the upper fourth of the zone, where 

 they are comparatively few. The fovea oc- 

 cupies the exact center of the circle and 

 shows as a dark pigment spot with its upper 

 two-thirds covered with black granules 

 closely spread above it fan-wise. 



The pecten has about 24 heavy, compact 

 convolutions that almost completely cover 

 the optic entrance. They are joined at the 

 irregular free border above by a translucent, 

 cigar-shaped band of tissue that extends 

 the whole length of the crest. 



The anterior and pointed terminal of the 

 papilla approaches to within less than a 

 disc width of the temporal boundary of the 

 macular region. 



European Cuckoo. Cuculus canorus. 

 The ocular fundus of this bird, as seen in 

 living specimens by the aid of the ophthal- 

 moscope, is depicted on Plate XLV, page 

 165. The picture is drawn of the left eye; 

 erect image. 



The coloration of the eyeground is gray 

 with a suggestion of fawn, everywhere show- 



ing minute, grayish-white dots. Towards 

 the lower quadrants of the fundus and in 

 particular at the extremity of the pecten the 

 background is suffused with a dull pink. 

 Near the optic nerve on either side are 

 several, plainly visible, orange-red choroidal 

 vessels. 



The macula is seen above the disc, towards 

 the nasal side. This area, slightly red in 

 tone, appears depressed below the fundal 

 plane, although no definite fovea is visible 

 with the mirror. 



The papilla is almost completely covered 

 by the pecten, so that only the outlines of 

 the former can be seen by the anteropos- 

 terior inspection of the ophthalmoscope. 

 Where the papillary margin is visible it 

 shows extremely white. 



The pecten also extends far above as well as 

 below the disc terminals and projects deeply 

 into the vitreous chamber. It appears by 

 the mirror to be a chocolate-brown in color. 

 Opaque nerve-fibre radiations are seen to orig- 

 inate at the disc margins, whence they cross 

 the background and finally disappear from 

 view at or near the periphery of the field. 



Piciformes 



Sulphur-breasted Toucan. Rhamphas- 

 tus lamiatus. As shown in Plate XL VI, page 

 165, this bird has a dull-gray eyeground (when 

 it is viewed ophthalmoscopically) rather regu- 

 larly spotted with whitish-gray dots. 



The optic papilla is apparently composed 

 of short, coarse, white fibres which form a 

 sort of fringe all round its margins. Along 

 each of its sides and parallel to its long diam- 

 eter a few orange-red, choroidal vessels are 

 seen. Radiating from the papillary circum- 

 ference are numerous opaque nerve fibres 

 that extend to the fundal periphery across the 

 eyeground on all sides. 



The pecten is almost black-brown in color 

 and in shape resembles the same organ in the 

 Hornbills and the Kingfishers, especially in 

 the former. 



Above the end of the optic nerve entrance 

 and about half its length to the nasal side are 

 three dark-brown spots, clustered together 

 and surrounded by a small gray reflex. This 



