100 VERTEBRATE PHOTORECEPTORS 



the nasal aspect of the optic disc. Such a type is found 

 in the common crow (Corvus americanus) and is illustrated 

 in Figure 72. An exception to the rule of the nasal position 



Fig. 74 (Left). Fundus oculi of the California valley quail (Lophortyx cali- 

 fornicus vallicola) showing absence of fovea. (From figure 110, Casey Wood, 

 1917.) 



Fig. 75 (Right). Fundus oculi of the stellar jay (Cyanocitta stelleri) showing 

 single nasal fovea. (From figure 111, Casey Wood, 1917.) 



Fig. 76 (Left). Fundus oculi of the British kingfisher (Alcedo ispida) showing 

 nasal and temporal foveae. (From figure 113, Casey Wood, 1917.) 



Fig. 77 (Right). Fundus oculi of the California shrike (Lanius ludovicianus 

 gambeli), showing nasal and temporal foveae. (From figure 141, Casey Wood, 

 1917.) 



of the single fovea apparently exists in the owls, where a 

 single, deep fovea enriched by a round sharply defined area 

 is located above and on the temporal side of the optic disc 



