FUNDUS OCULI OF BIRDS IN PREPARED SPECIMENS 



55 



Fig. 107. 

 California Shrike (Lanius ludovicianus gainbeli) . 



Fig. 108. 

 American Crow (Corvus americanus). 



Fig. 109. 

 Steller Jay (Cyanocitta stelleri) X12. 



Lateral View of the Pecten in the Prepared Eyes of 

 Certain Species of Birds. 



The Retina and the vessels of the choroid are 

 practically invisible in the eyes of birds viewed 

 macroscopically a few minutes after death. 

 However, when treated with Perenyi's fluid 

 and other preservatives or especially in case of 

 successful carotid injections, the choroidal 

 bloodvessels and tissues become more opaque 

 or at least more translucent and may then be 

 studied with success. Doubtless the oph- 

 thalmoscope gives us the one best means of 

 seeing these tissues as they exist during life, 

 but both methods, supplemented by the mi- 

 croscope, are needed for a complete study of 

 them in all their relations. Very little light is 

 thrown on these questions by naked-eye ob- 

 servations of the choroidal vessels, although in 

 some birds, especially when injections of car- 

 mine have been made, they are quite evident. 

 Serial sections, in conjunction with the use of 

 the ophthalmoscope, afford the best means 

 of studying these fundal vessels. 



The pigment deposits and other histological 

 elements in the choroid and retina — espe- 

 cially in the former — that combine to make 

 or modify the general coloration of the fundus 

 oculi are best seen with the ophthalmoscope; 

 prepared specimens furnish but slight indi- 

 cations of these. Differences of level, as in 

 the macular areas, are, however, well shown 

 macroscopically. 



Areas of Distinct Vision. As a result of 

 the investigations of Slonaker and the writer 

 it may be said of Birds with but a single 

 fovea that this sensitive area is generally 

 placed about the center of the retina, slightly 

 above and towards the nasal aspect of the 

 optic nerve entrance. This observation is 

 practically illustrated in a number of pictures 

 reproduced in this work from the drawings of 

 Kennedy and the paintings of Head. See, 

 for example, the drawings of the fundus views 

 of Sialia sialis (Fig. 140), Corvus americanus 

 (Fig. 142) and Nycticorax nycticorax (Fig. 129), 

 in which a single, deep, well-defined fovea is 

 present. 



An exception to the rule of the nasal posi- 

 tion of the single fovea? and macular regions is 

 noticeable in the Owls. These birds possess 

 a single, deep fovea encircled by a round, 

 sharply defined area located above and on 



