102 VERTEBRATE PHOTORECEPTORS 



1. The Amacular Fundus. Those which show no evidence 

 of a central macular region either with the ophthalmoscope 

 or in preserved material. This is illustrated by the California 

 quail (Figure 74). Upon histological examination such fundi 

 exhibit a retinal area (area centralis retinae) more specialized 

 for distinct vision than the surrounding retina. Apparently 

 such fundi are rare and found mostly in domestic birds. 

 Wood quotes Slonaker as having described a shallow ill- 

 defined area centralis in the turkey and guinea hen, and a 

 very slight thickening in the cock (Gallus). 



2. The Nasal Monomacular Fundus. This is situated in the 

 center of the retina and is found in the majority of birds 

 (Figure 75). 



3. The Temporal Monomacular Fundus. This form is 

 found exclusively in the owls and is illustrated by the 

 European barn owl in Figure 73. 



4. The Bimacular Fundus. Here two foveas occur — the 

 nasal, which is the principal one and usually deeply marked, 

 and a less developed temporal fovea. This is illustrated by 

 the kingfisher in Figure 76 and also by the swallow (Figure 69). 



The bimacular fundus exhibits two varieties, viz., those 

 with a more highly developed nasal macular region where 

 the fovea is sharp and well defined (e.g. swallow), and those 

 where the temporal macular region is more marked, and with 

 a deeper fovea than in the nasal region (e.g. hawks). 



5. Band-like Area Centralis. In this band or stripe there 

 exists a well-defined fovea or macula. This is the type which 

 Wood has designated as the infulamacular fundus. It 

 is illustrated in Figure 70. The fovea included in this band 

 is found on the nasal side of the fundus. 



6. Infulabimacular Fundus. In this type of specialization, 

 two macular regions are either joined or are associated with 

 the band-like area (Figure 71). This form of specialization 

 presents two varieties. The one is characterized by a well- 

 defined nasal macula with a deep fovea situated near the 

 center of the retina, and a shallow temporal macula. These 

 two are joined by a short ribbon-like area which does not 



