THE FUNDUS APPEARANCES IN VARIOUS ORDERS OF BIRDS 



73 



quadrants of the fundus by the mirror) very 

 sensitive to light there is no other ophthal- 

 moscopic indication of a macular region. 



The long optic disc is white, with a few 

 tiny pigment dots about its margins. The 

 pecten is lighter brown than in the majority 

 of birds; it is very large, almost hiding 

 the disc from view. Many opaque nerve 

 fibres radiate from the papillary circum- 

 ference and extend several disc breadths 

 across the fundus. Owing to the large size 

 of the pecten and the small pupil it is im- 

 possible to obtain a satisfactory lateral view 

 of the pecten, which almost covers the pupil- 

 lary area with its massive club-shaped end. 



The American congener of this bird — 

 Fulica americana — has a fundus almost identi- 

 cal, ophthalmoscopically,with this species. 



Ipecaha Rail. Aramides ipecaha. The 

 ophthalmoscopic picture of this bird, rep- 

 resenting the right eye, is seen as Plate XIII, 

 page 133. 



The eyeground is a very pale uniform gray 

 stippled with darker gray and white dots, 

 thus giving the whole field a granular ap- 

 pearance. 



The horizontally oval macular area (on 

 the nasal aspect near the upper end of the 

 disc) assumes a pinkish tone. At its center 

 is a small pit which, in the light of the mirror, 

 appears as dark gray with a brilliant, white 

 central dot. Around the macular region is 

 a pale, blue-gray reflex, which loses itself in 

 the general tone of the fundus but appears 

 quite sharp on the inner side of the oval 

 macular region. 



The disc is a narrow, white oval, whose 

 major axis measures about one-third the 

 height of the pecten. A number of opaque 

 nerve fibres run across the background at 

 right angles to the papilla and fade into the 

 general gray of the fundus. 



The pecten arises from the upper segment 

 of the disc, spreads out on it like the root of 

 a tree and gradually disappears into the 

 papillary substance. From this root a long, 

 slender, spiral form projects into the vitreous. 

 It is brown in color, is of uniform width, 

 looks like a corkscrew and extends forwards 

 and outwards as far as the eye can see, 



looking as if it were pressed against the lower 

 part of the lens. The anterior end of the 

 pecten is much darker in color than its pos- 

 terior half, which is quite flat. 



The fundus oculi of the Weka Rails (Ocy- 

 dromus) is quite similar to the ocular back- 

 ground of this specimen. 



Podicipediformes 



Great Crested Grebe. Podicipes 

 cristatus. (Figs. 121 and 83.) A macro- 

 scopic examination of the fundus oculi in 

 this species reveals a broad retinal band, uni- 

 form in width, that extends from the nasal 

 periphery across the fundus and is lost in the 

 pigment of the opposite side. It is half as 

 wide as the minor axis of the oval disc and, 

 along its whole length, is depicted by two 

 parallel lines of pigment dots — the inferior 

 border containing the more numerous grains. 

 The nasal half of the wide band is bisected 

 by a narrower, almost linear, ribbon com- 

 posed of minute black dots that are most 

 numerous at the periphery of the field, 

 becoming fainter and fainter until just 

 before the macula is reached, when they 

 disappear altogether. 



At about a long papillary diameter from 

 the superior end of the pecten and on its 

 nasal side, is a large, circular, partly pig- 

 mented, disc-like macular region arranged 

 within and somewhat exceeding the limits 

 of the retinal band. It has, in its turn, a 

 central, depressed lighter area, surrounded 

 by a small ring of pigment. 



The pecten covers the optic entrance, and 

 has the steam radiator-like form of the 

 Wonga Dove. However, this species ex- 

 hibits 24 convolutions, the free border shows 

 three definite elevations above and it has a 

 deep, opaque keel to which all 12 double 

 folds are firmly united. 



The angle made by projecting the major 

 axis of the oval optic papilla until it bisects 

 the lower border of the retinal band, the 

 infulapapillary angle, is, approximately, 70°. 



In injected specimens of this species (as 

 well as occasionally in individuals not so 

 treated) the choroidal vessels show very 

 plainly. 



