110 



THE FUNDUS OCULI OF BIRDS 



disc-length from the anterior end of the optic 

 entrance. 



The long and wide pecten has 54 single con- 

 volutions, and in shape resembles the same 

 organ in the Shrike, except that from the 

 center of its crest rises a short spine easily 

 seen in both figures. The optic papilla is 

 almost completely hidden by the mass of the 

 marsupium. 



American Crow. Corvus americanus. 

 (Figs. 108 and 142; macroscopic view). There 

 is in the background of this species an area 

 of acute visual perception represented by a 

 retinal bar or band at whose middle point is 

 seen a well defined fovea, the center of a macu- 

 lar region formed by a widening of the band 

 itself. The band stretches horizontally across 

 the fundus and is centrally located in the 

 field of view. It is of medium width, out- 

 lined by a uniformly dotted line above, but 

 less distinctly below by a string of minute 

 granules that more or less tint the lower half 

 of the band itself. The macular region is 

 formed by a widening of the sensitive band to 

 form an oval-shaped region. 



The superior end of the papilla is one-half 

 its length from the foveola. 



The large pecten (three-fourths the length 

 of the retinal band) is formed of about 52 

 uniformly compressed convolutions joined 

 at their free margins, above, by a shallow, 

 dumb-bell-shaped crest that slopes gradually 

 from behind forwards. 



If the major axis of the papilla — obscured 

 by the pectinate mass — were projected to 

 meet the temporal end of the retinal bar it 

 would describe an (infulapapillary) angle of 

 about 60°. 



European Carrion Crow. Corvus 

 corone. The writer examined in the Labora- 

 tory of St. Luke's Hospital, Chicago, an 

 adult male of this species, imported from 

 Germany. He had been in captivity about 

 a year. Both eyes were healthy. He used 

 his nictitating membrane freely on the ap- 

 proach of light to the eye. The pupils varied 

 in diameter from 2 to 4.50 mm. A single 

 drop of 1% solution of atropine sulphate into 

 each eye produced no effect on the size or 

 movements of the pupils during the following 



48 hours. The same negative result was ob- 

 tained by the use of a one-fifth per cent solu- 

 tion of hyoscin and by a mixture of homatro- 

 pine and cocaine. Skiascopy in the dark 

 room showed, both before and after the use 

 of atropia, a hyperopia of 2D. 



By the direct method the background 

 appears to be almost uniformly dark red- 

 brown. The macular region is seen with 

 difficulty. 



The optic disc is a long, white oval with 

 the pecten a very black, corkscrew-like organ, 

 apparently changing place and shape rapidly 

 under examination. 



Common British Blackbird. Turdus 

 merula. The ophthamoscopic picture of this 

 species is reproduced as Plate LVII, page 177. 

 It shows the eyeground as seen in the left eye 

 by the direct method. The general tint is a 

 slaty-gray with a uniform sprinkling of tiny, 

 white dots. There is no visible macular 

 region, but the whole fundus is covered and 

 its coloring greatly modified by numerous, 

 linear, opaque fibres that arise from the disc 

 margins throughout and run across the entire 

 fundus to the extreme periphery. A few 

 faint, yellow-red choroidal vessels are seen on 

 either side of and parallel to the moderately 

 long and narrow papilla. The upper two- 

 thirds of the disc is about half covered by the 

 club-shaped pecten, which is apparently com- 

 posed of very few folds. The massive, choco- 

 late-colored, posterior end of this organ en- 

 tirely obscures the lower third of the nerve- 

 head, while the upper half of the former has 

 a light brown margin on its nasal aspect, and 

 seems to be only in part attached to the nerve- 

 head beneath it. 



Raven. Corvus corax. The fundus picture 

 (right eye) shown by Plate LVIII, page 177, 

 represents the (similar) appearances in a 

 number of specimens examined with the 

 ophthalmoscope by Mr. Head in the London 

 Zoological Gardens and by the writer in the 

 aviary of the Bronx Park, New York. 



The eyeground is a light fawn sprinkled 

 with dots about three shades darker than the 

 ground color. Mixed with the dark dots 

 are numerous white ones, seen especially when 

 a strong light is thrown upon the fundus. 



