THE FUNDUS APPEARANCES IN VARIOUS ORDERS OF BIRDS 



85 



The optic nerve-entrance is a long, narrow 

 oval, and presents a brilliant white appear- 

 ance. Near its upper end are several choroi- 

 dal capillaries of a pale, golden-yellow color. 

 Parallel to the long axis of the nerve-head is 

 another elongated mass of white fibres * 

 (almost like a second optic disc) having its 

 center stippled with fine pigment dots, and 

 extending across the eyeground. Radiating 

 from the circumference of the papilla one 

 sees a number of faint, translucent fibres, 

 crossing the small white area on the nasal 

 side of the nerve. 



The pecten does not project very far 

 forward into the vitreous; it is dark gray- 

 brown and appears to be completely covered 

 with a number of warty protuberances. 

 It appears to be attached to the whole length 

 of the centre of the disc, that is stippled 

 with fine, red dots. 



Anseriformes 



Black-bellied Tree Duck. Dendro- 

 cygna autumnalis. The fundus appearances, 

 as revealed by the ophthalmoscope in six 

 eyes of three individuals, are depicted as 

 Plate XXVI, page 145. Five normal eye- 

 grounds were identical; the sixth exhibited a 

 congenital defect of the nerve-head which 

 entirely changed the fundal picture. 



The fundus oculi of the Tree Duck is colored 

 a light fawn, besprinkled with minute, white 

 dots, that glisten when a strong light from 

 the mirror is thrown upon them. On each 

 side of the papilla is seen a number of choroi- 

 dal capillaries, bright orange in color and 

 rather straight. 



The optic disc is also orange-red along its 

 major axis, this central zone being stippled 

 all over with a network of fine black dots. 

 The circumference of the disc is fringed with 

 white fibres. 



The dark-brown pecten arises, as usual, 

 from the whole length of the disc. Viewed 

 from above it seems very thin and twisted, 



* Whether this is a normal condition or an anomaly 

 of development cannot be definitely stated without 

 an examination of additional specimens, but it was 

 present in both eyes of the individual under con- 

 sideration. 



like a corkscrew. A few opaque nerve 

 fibres extend for a short distance and at 

 right angles to the disc on either side. The 

 upper part of the fundus is almost obscured 

 by numerous minute, brilliant, white dots. 

 Although Head noticed that when he focused 

 the bright light of the mirror on the upper 

 quadrants of the fundus the Ducks used 

 their membrana nictitans more frequently 

 than usual he could not discover any well- 

 defined sensitive area. 



Blue-winged Teal. Querquedula dis- 

 cors. The general appearance of this bird's 

 eyeground closely approaches that of the 

 Mallard. The long, ovoid papilla is disposed 

 with its major axis at right angles to the 

 upper mandible. 



Mandarin Duck. Aix galericulata. In 

 examining the eyeground of this species the 

 writer found that the light of the ophthal- 

 moscopic mirror, when projected on the 

 eyes directly from the front, illuminates, 

 roughly speaking, about one-sixth of each 

 field. ' 



The prevailing color of the background 

 is light, gray-brown, streaked with faintly 

 marked choroidal capillaries, that are, 

 however, confined to the nasal side of the 

 disc. 



The direct method shows a vertically 

 placed optic entrance, that appears to stretch 

 almost over the whole fundus. The field on 

 the outer aspect of the disc seems to be 

 superficially roughened or granular. There 

 are no radiating opaque nerve-fibres or con- 

 centric reflex rings visible with the mirror. 



The pecten is comparatively small, does not 

 entirely cover the disc and presents from 

 above downward a reticulated appearance. 



Mallard Duck. Anas boscas. The 

 general coloration of the fundus of this bird is 

 gray-red. The optic nerve entrance is much 

 longer than in most species, extending in a 

 perpendicular fashion across the background; 

 it is in no place obscured or entirely hid by 

 the pecten. The papilla appears to be 

 attached for three-fourths of its course to 

 the latter, which arises in partially trans- 

 lucent, veil-like folds and extends to the 

 posterior surface of the lens. No concentric 



