44 



THE FUNDUS OCULI OF BIRDS 



One finds examples of this form in Columba 

 palumbus (Fig. 33), Cuculus canorus (Fig. 66), 

 Catheturus lathami (Fig. 31), Larus argentatus 

 (Fig. 39), L. marinus (Fig. 40), Rhinochetus 

 jubatus (Fig. 43), Goura victoria (Fig. 34), 

 Chen cerulescens (Fig. 48), Mycteria americana 

 (Fig. 47), Speotyto cunicularia (Fig. 57), 

 Stringops habroptilus (Fig. 62), Chrysotis 

 amazona (Fig. 60), Rhea americana (Fig. 25), 

 Sula bassana (Fig. 50), Haliaetus leucogaster 

 (Fig. 54), Cacatua galerita (Fig. 61), Den- 

 droma autumnalis discolor (Fig. 49), Crax 

 globosa (Fig. 32), Fratercula arctica (Fig. 38), 

 Dacelo gigas (Fig. 63), and Botaurus stellaris 

 (Fig. 44). 



III. This class includes those pectens (usu- 

 ally of slender proportions) that arise from the 

 whole surface of the optic papilla and, then, 

 either curve towards and folloio the concave wall 

 of the eyeball or they proceed in a straighter 

 line until they touch (or nearly reach) the poste- 

 rior surface of the lens, generally near its 

 equator. In most instances there is less than 

 a disc length between the pecten terminal and 

 the lens capsule. To this class belong the 

 pectens of Hirundo rustica (Fig. 71), Leu- 

 cosarcia picata (Fig. 35), Cyanospiza versicolor 

 (Fig. 73), Mimus polyglottos (Fig. 72), Spago- 

 lobus adratus (Fig. 64), Xanthura cyanocitta 

 (Fig. 75), Aramides ipecaha (Fig. 36), Apteryx 

 mantelli (Fig. 27) and Coturnix histrionica 

 (Fig. 30). 



These are many species whose pectens 

 occupy a position intermediate between 

 Class II and Class III, and which are conse- 

 quently, not easy to place. Of those that are 

 figured in the text may be mentioned Rham- 

 phastus laematus (Fig. 67), Otis tetrax (Fig. 42), 

 Dendrocopus major (Fig. 68), Phalacrocorax 

 carbo (Fig. 51), Corvus cor ax (Fig. 76), Centurus 

 uropygialis (Fig. 69), Pitangus derbianus (Fig. 

 70) and Cariama cristata (Fig. 29). 



Opaque nerve-fibres. As previously stated, 

 the neurilemma, or nerve-sheath, of the 

 opticus is in many Birds, as occasionally in 

 Man, continued into the retinal substance. 

 These nerve-fibres are easily seen in the avian 

 fundus when viewed with the ophthalmo- 

 scope, although in preserved eyeballs they are 

 invisible to the naked eye. 



In some instances they radiate from the 

 nerve-head as whitish, thread-like rays, in 

 such a fashion as to cover the whole of a 

 wide area about the optic entrance. This 

 condition is well shown in Turdus merula 

 (Plate LVII), Spagolobus adratus (Plate 

 XLIII), Rhamphastus laematus (Plate XL VI), 

 Plegadis falcinellus (Plate XXIII), and Tin- 

 nunculus alaudarius (Plate XXXV). 



As a rule, however, the avian fundus is free 

 of these nerve elements; in all probability 

 they interfere to some slight extent with 

 general retinal vision and are consequently 

 absent in those genera requiring the most 

 acute visual powers. They are few in num- 

 ber or are entirely absent in Night Birds, and 

 in such representative species as Gypaetus 

 barbatus (Plate), XXXII Casuarius occipitalis 

 (Plate III), Haliaetus leucocephalus (Plate 

 XXXIII) and Rhinochetus jubatus (Plate 

 XVIII). 



They are short or inconspicuous in all the 

 acarinate birds, so far examined, including 

 the Tinamou (Plate V) as well as in 

 Nycticorax nycticorax (Plate XX), Crax glo- 

 bosa (Plate VI), Coturnix histrionica (Plate 

 VIII) and Phalacrocorax carbo (Plate XXVIII). 



E. Photography of the Fundus Oculi in 

 Living Birds 



Many attempts have been made to photo- 

 graph the fundus oculi through the pupil in 

 living subjects — to combine, as it were, 

 photography with ophthalmoscopy. If this 

 scheme is ever put into practical operation, 

 especially if it be found possible to photograph 

 the eyeground in its natural colors so that 

 the negative can be reproduced and published, 

 a great advance will be made over the re- 

 stricted (because slow and expensive) plan 

 per force adopted by the writer. Photog- 

 raphy of the colored details of the fundus 

 would render unnecessary either the expert 

 ophthalmologist or the trained artist, while 

 the number of avian backgrounds explored 

 by such exact methods would soon be counted 

 by hundreds where they are now registered by 

 units. Moreover, as the ophthalmoscopic 

 picture is to a certain extent differently inter- 

 preted, and correspondingly described and 



