84 



THE FUNDUS OCULI OF BIRDS 



a bright, irregular and linear reflex surrounds 

 the macular region, which is very sensitive to 

 light. 



There is a long, narrow papilla with rounded 

 extremities. It appears as if it were com- 

 posed of short, white fibres, surrounding an 

 orange-red center covered with minute, dark- 

 brown pigment grains that form a network 

 over the whole red area. Extending from 

 each side of the disc across the retina are a 

 few dull-gray, opaque nerve fibres. 



The pecten can be traced the whole length 

 of the disc; it is dark brown in color and 

 grooved spirally like a corkscrew. It does 

 not appear to come far forward towards the 

 lens, and its union with the nervehead can 

 readily be traced. The pecten and its im- 

 mediate relations remind one of the fundus 

 oculi of the Bitterns. 



Glossy Ibis. Plegadis falcinellus. As 

 will be seen on examining Plate XXIII, page 

 143, representing the left fundus oculi of this 

 species, the general coloration is blue-gray, 

 the eyeground being covered with a nebula of 

 minute, pale-gray dots, giving it a brilliant 

 gray tone when lighted up by the rays from 

 the ophthalmoscopic mirror. 



Towards the lower part of the fundus and 

 on both sides of the optic disc, but parallel 

 with it, are many orange-red choroidal capil- 

 laries; they are especially numerous below 

 the optic nerve and suffuse the peripheral 

 background with an orange-pink glow. 



Only one sensitive area is seen. This 

 macular region is located above the disc on the 

 nasal side of the nerve. In the center of the 

 area is a small, white, round dot, surrounded 

 by a brilliant blue-green reflex, like the sheen 

 on floss silk. It is probably due to the play 

 of light on the fine fibres radiating from the 

 center of the fovea. 



The optic disc looks as if it were a mass 

 of coarse white fibres; it is similar in shape 

 to the papilla of the Spoonbill, but it can 

 be traced only for about half its length, 

 the lower part being obscured by the mas- 

 sive club-shaped pecten. The disc is bor- 

 dered with black pigment which gives the 

 appearance of a shadow cast on the eye- 

 ground. This organ is of the usual chocolate- 



brown color and projects well forward towards 

 the lens. 



A large number of semi-translucent nerve 

 fibers radiate from the margins of the optic 

 nerve on all sides; they extend across the 

 choroidal vessels, and finally vanish alto- 

 gether in the fundal periphery. 



American Jabiru. Mycteria americana. 



The fundus of the left eye is depicted in 

 Plate XXIV, page 143 by the direct method. 

 The general coloration is a slate-gray, the 

 whole eyeground being quite uniformly 

 sprinkled with small but variously sized, 

 white dots. In the upper and nasal quadrant 

 of the picture is the small, single macula, an 

 area darker than the surrounding parts, whose 

 exact centre shows a round white dot — the 

 fovea. In the lower two-thirds of the field 

 are seen numerous, plainly marked choroidal 

 vessels that extend the whole length of the 

 pecten, converging somewhat towards the 

 posterior aspect of its base. About two- 

 thirds of the long and rather broad nerve-head 

 is plainly visible, except the central portion, 

 which is partly obscured by the pecten. This 

 large, black-brown organ, divided into 15 

 large and several much smaller double folds, 

 terminates above as a thin, dark rod. The 

 disc is fringed by black pigment grains, and 

 from its lateral margins project a number of 

 short, faint, whitish lines. 



Spoonbill. Platalea leucorodia. The col- 

 ored fundus view (see Plate XXV, page 145) 

 is of the erect image, left eye. In general 

 the color of the eyeground is decidedly gray, 

 becoming brownish towards the periphery. 

 It will be noted that the entire fundus is 

 thickly sprinkled with minute, irregularly 

 shaped, gray-white dots, that appear more 

 distinct about the macular region. 



At the fovea, where they are brilliant 

 white, they are still more closely packed. 

 With the ophthalmoscope the foveal region 

 appears to be sunken below its surround- 

 ings, and to be enclosed in a pale, greenish 

 (reflex) ring that is of oval shape with its 

 long axis horizontal. Judging from the 

 effect on the bird when the direct light from 

 the mirror is thrown upon it, this area is 

 extremely sensitive to light. 



