THE FUNDUS APPEARANCES IN VARIOUS ORDERS OF BIRDS 



77 



crest or keel is elevated to a sharp point, 

 and towards which the other folds are in- 

 clined. They gradually decrease in size 

 towards both the posterior free margin — 

 an unusual disposition — and to the anterior 

 or superior terminal of the optic entrance, 

 in accordance with the rule. 



The longer axis of the disc projected until 

 it meets the retinal band makes with the 

 latter an infulapapillary angle of about 65°. 



Puffin. Fratereula arctica. The eye- 

 ground of this remarkable species is portrayed 

 as Plate XV, page 135. It represents the 

 left eye as seen by the direct ophthalmo- 

 scopic method. 



The general color of the eyeground is red, 

 rather uniformly stippled with small, mixed, 

 light-red and dark-gray dots. Above the 

 upper end of the optic disc and towards the 

 temporal side is a small, round, red area sur- 

 rounded by a pale, light-gray film, shot with 

 bright lines on the outer and inner margins — 

 doubtless the macular region with its central 

 fovea. Head noticed that not only this area 

 but most of the upper half of the fundus is 

 very sensitive to light. 



The optic papilla, oblong, narrow and with 

 a rounded upper extremity, lies low down in 

 the eyeground, while the pecten extends well 

 forward and behind the lower margin of the 

 pupil. A view of the nerve-head is much 

 obscured by the body of the massive pecten 

 which almost covers it when seen, as with the 

 mirror, from above downward. The small 

 segment visible with the ophthalmoscope 

 appears not brilliant white but rather a bluish- 

 white, the margins of the pecten being covered 

 with black pigment. 



Extending at right angles to the disc on 

 both sides are a few very fine, gray opaque 

 nerve fibres, that finally disappear in the 

 fundal periphery. The pecten is of the usual 

 chocolate-brown color and comes well for- 

 ward towards the lens, especially in its infe- 

 rior aspect. 



Lariformes 



Herring Gull. Lotus argentatus. (Figs. 

 124 and 86; macroscopic view.) In this 

 species the upper and more pointed extremity 

 of the pecten points slightly to the temporal 



side of a linear fovea that is drawn as a rather 

 broad, short, retinal band that skirts the clear 

 area and stretches in a slightly oblique direc- 

 tion across about one-third of the central 

 field. The foveal slit (nearly as long as the 

 optic disc is wide) occupies a widened portion 

 of the band-like process and shows a line of 

 pigment dots along its upper margin. 



The very broad, long pecten covers an 

 equally large papilla. It has 36 thin, leaf -like 

 convolutions which, in prepared specimens, 

 do not obscure the margins of the nerve-head, 

 whose canoe-shaped outlines are everywhere 

 visible from above, except at the bow and 

 stern. The free border, comparatively wide, 

 is deeply pigmented, does not reach the supe- 

 rior extremity of the pecten and has the 

 appearance of an ear of maize. The medial 

 and posterior leaflets of the pecten are the 

 longest, only the anterior five becoming 

 smaller as they approach the upper extremity 

 of the papilla. 



The inf ulapapillary angle measures about 60? 



The ophthalmoscopic appearances of the 

 background are the same in both the European 

 and New World species. A large number of 

 healthy individuals were examined both by 

 Mr. Head and the writer. 



The ocular background of this bird is quite 

 similar to that of Larus marinus. The 

 prevailing color is dull brown, the upper half 

 being interspersed with masses of small gray 

 dots, that assume a pink hue downwards 

 from the upper end of the optic disc. One 

 notices in this region, also, many dull-red, 

 choroidal capillaries that run parallel to the 

 sides of the elongated nerve-head. 



A little above the upper end of the papilla, 

 towards its inner or nasal side, is the fovea 

 centralis, a brownish red dot, in the centre of 

 a rather dull area. This macular region is 

 enclosed by two clear, bright green rings, or 

 reflex circles. 



The optic disc (papilla) appears to be made 

 up of very short, brilliant white and rather 

 coarse opaque nerve fibres. Extending from 

 its margins are a few, dull-gray, opaque nerve 

 fibres, that radiate from the elongated papilla 

 but fade away in the periphery of the back- 

 ground. 



