FUNDUS OCULI OF BIRDS IN PREPARED SPECIMENS 



59 



words the disposition of the areas for acute 

 vision assumes this form in Birds that take 

 their prey on the wing or by darting upon it 

 from a distance. 



A Classification of Areas of Distinct Vision 

 in Birds 



From the foregoing it may be concluded 

 that there are at least six arrangements of 

 these areas, and consequently six forms of 

 apparatus for securing acute eyesight in birds. 

 These may be classified as follows: 



1. The amacular fundus, in which, as in 

 the California Valley Quail (see Fig. 110), 

 there is to be seen neither with the ophthal- 

 moscope nor in preserved material any indica- 

 tion of a central macular region; rather a rare 

 class. It is only by a microscopical examina- 

 tion of serial sections that one sees the his- 

 tologic elements indicative of an area of 

 vision more specialized for distinct visualiza- 

 tion than the surrounding retina. Such fundi 

 are rare, and are found, for example, in a 

 few domestic birds. Slonaker discovered a 

 shallow and ill-defined central area in the 

 Turkey (Meleagris gallopavo) and the Guinea 

 Hen (Numidia pucherani); also "a very 

 slight thickening," instead of a fovea, in the 

 Cock (Gallus domesticus). 



2. The nasal monomacidar fundus, situated 

 in the centre of the retina, is found in the 

 majority of birds. An example is shown in a 

 drawing of the eyeground of the Steller Jay (see 

 Fig. 111). As a rule, it is best demonstrated 

 macroscopically, although even a cursory ex- 

 amination of the colored plates in this work 

 will reveal numerous examples of this form of 

 fundus when viewed ophthalmoscopically. 



3. The temporal monomacidar fundus is 

 found almost exclusively in the Owls. An 

 example of this form is seen in the European 

 Barn Owl (Fig. 112); indeed in all the Strigi- 

 formes whose fundi are pictured or described 

 in this monograph. 



4. The bimacular fundus, in which there 

 are two macula?, generally a deeply marked 

 and principal nasal region and a subsidiary 

 temporal area. See Fig. 113, representing a 

 macroscopic view of the (preserved eyeball) 

 fundus of the Belted Kingfisher. 



There are two sub-varieties of this fundus; 

 (a) certain eyes of regular form in which the 

 nasal macular region is well developed and 

 the fovea is deep and sharply defined, as in 

 Alcedo, Sterna and Tachycineta; (b) in birds 

 with eyes of irregular shape, exhibiting a 

 deeper temporal fovea and better marked 

 macular region. These are found in the 

 Hawks especially. 



5. A band-like central area with which is 

 almost invariably associated a well-defined 

 fovea or macula. To this form of avian back- 

 ground the writer has given the name infula- 

 macular* fundus. As an example, see Fig. 

 114, showing a macroscopical view of the eye- 

 ground in the Greater Yellow-legs (Totanus 

 melanoleucus) . In this class the band in- 

 closes, in some part of its course, the single 

 fovea which in its turn is found on the nasal 

 side of the fundus. 



6. Finally, in some avian backgrounds 

 there are two macular regions, either joined to or 

 associated with the band-like area, to which the 

 name infulabimacular fundus has been given 

 by the writer. An ocular background of this 

 description is seen in the Common Flamingo. 

 See Fig. 115. There are at least two varieties 

 of this form. 



The Sparrow Hawk (Falco sparverius) and 

 Buteo borealis furnish examples of form (a) — 

 a well-defined nasal macula with a deep fovea 

 situated near the centre of the retina and a 

 shallow though easily demonstrable temporal 

 macula, the two joined by a short ribbon- 

 like area. The band area does not extend 

 beyond either macular region. 



In second form (b), represented by the Tern 

 (Sterna hirundo), the band-like area encloses 

 a nasal macula while a second (temporal) 

 macular region lies above and apart from 

 these. 



Even a slight acquaintance with the fundi 

 oculorum of the comparatively few Birds so 

 far examined shows not only numerous types 

 of areas centrales, but a still greater variety in 

 their size, shape and appearance, both mac- 

 roscopical and ophthalmoscopical. These are 

 most distinctly marked in the prepared speci- 

 mens. Some Birds exhibit a large, circular 

 *Infula, a band or ribbon. 



