104 



THE FUNDUS OCULI OF BIRDS 



There seems to be only one sensitive central 

 area. This single macula is, as usual, on the 

 nasal side of the pecten and has the appear- 

 ance of a brilliant, white, round dot, the fun- 

 dus surrounding it being a little darker than 

 the general color of the eyeground. The sur- 

 rounding gray area makes the white fovea 

 stand well forward, almost as if it were actu- 

 ally situated in the vitreous. No reflex ring 

 can be seen around it. 



Passeriformes. A. Mesomyodi 



Derby Tyrant. Pitangus derbianus. 

 The fundus view of this species, shown by 

 Plate XLIX, page 169, represents ophthal- 

 moscopic examinations of three specimens. 

 The six eyes of the three birds presented pre- 

 cisely the same ophthalmoscopic appearances. 



The eyeground is blue-gray, everywhere 

 sprinkled with minute, gray dots. These 

 dots are so closely packed in the upper half 

 of the fundus that they give it a distinct 

 silvery appearance. Running at right angles 

 to either side of the optic papilla are numerous 

 dull-white opaque nerve fibres. These are 

 near together and extend well across the eye- 

 ground. 



At right angles to the optic disc towards 

 the nasal side and a little above its superior 

 end is a dense, pale-blue, punctate mass that 

 appears to surround the fovea. A light-blue 

 reflex ring also encircles this area. 



The optic nerve-entrance is long, narrow and 

 white. Its centre is stippled with a few 

 brown pigment dots, and it is bordered all 

 around with symmetrically placed black pig- 

 ment granules. This pigmented margin 

 varies a little in individuals. The pecten, 

 long and narrow, extends well behind the 

 edge of the pupil so that a portion of it can- 

 not be seen through the mirror. The upper 

 part is serrated but the lower half is more of 

 the corkscrew type. The color is the usual 

 deep, dull brown. 



Passeriformes. B. Acryomodi 



European Chimney Swallow. Hirundo 

 rustica. The ophthalmoscopic appearances in 

 this species are shown on Plate L, page 169, 

 and depict the erect image of the right fundus. 



The general color of the eyeground is warm 

 gray, tinted slightly with yellow or buff, and 

 covered with minute, dull, yellowish dots. 

 Several pale orange (choroidal) blood-vessels 

 are seen near the upper extremity of the optic 

 nerve-entrance. 



There are visible two macular regions, one 

 on each side of and above the upper end of 

 the disc. They show as small brown areas 

 or dots in the eyeground. Surrounding the 

 temporal macula is a slight reflex, apparently 

 composed of minute, bright gray dots. The 

 macula on the nasal side is quite devoid of 

 this reflex-ring. 



The optic papilla, long and narrow, tapers 

 at its upper end. On either side of the disk, 

 and at right angles to it are a few, fine, dull- 

 gray opaque nerve-fibres. 



The pecten is quite narrow at its junction 

 with the optic nerve, but it gradually becomes 

 wider and more massive as it approaches the 

 lens. It is of the usual chocolate-brown color, 

 and is convoluted. 



Western Mockingbird. Mimus poly- 

 glottos leucopterus. (Figs. 105 and 139; mac- 

 roscopic view). In this fundus are seen two 

 sensitive areas. The area nasalis, lying above 

 and anterior to the superior end of the optic 

 entrance about half the length of the papilla, 

 is seen as a black spot capped on its temporal 

 aspect by a semi-circle of large pigment 

 grains. The whole macular region is not 

 only bordered by pigment but the intervening 

 zone is, in the nasal three-fourths, also 

 sprinkled with minute granules. The area 

 temporalis is placed almost directly posterior 

 to but much farther from the upper end of 

 the disc than the nasal fovea. It is evidently 

 shallower, is less plainly outlined and the 

 foveola is not as large. [The black line run- 

 ning along the left side of the large figure 

 indicates that a segment of the globe has been 

 removed — to show the temporal macula.] 



The very long, narrow pecten has 52 single, 

 compact convolutions that everywhere hide 

 the optic entrance. A moderately deep and 

 wide keel unites the pectinate folds along the 

 upper free border of the pecten almost to its 

 junction with the superior, pointed end of 

 the disc. 



