Chapter VII 



MACROSCOPIC APPEARANCES OF THE FUNDUS OCULI OF 

 BIRDS IN PREPARED SPECIMENS 



This subject has to some extent been dis- 

 cussed in Chapters IV and IX. As previous- 

 ly stated, the actual appearance, arrangement 

 and relations of the organs in the Bird's 

 fundus — pecten, retina, optic nerve, choroid 

 and choroidal bloodvessels, macular regions 

 (areas of distinct vision) — can be readily per- 

 ceived in properly preserved eyeballs. Im- 

 mersed in Perenyi's fluid and a series of 

 alcohols and otherwise carefully prepared, an 

 equatorial section of an avian globe furnishes 

 material for a satisfactory macroscopic study 

 of many of the parts in the interior of the eye. 

 The gross relations of these parts in typical 

 birds are seen in Figs. 1, 5, 6, 7, and 11. 



The Pecten is probably always somewhat 

 shrunken and more or less displaced even in 

 the freshest and best preserved specimens; 

 so that allowance must be made (in examining 

 prepared material) for that fact. This is the 

 reason, perhaps, that Apteryx was for several 

 generations credited with absence of a pecten, 

 until Lindsay Johnson proved its presence in 

 that bird. The peculiar construction of the 

 small marsupium in the Kiwi not only made 

 it easy of reduction in volume but it was also 

 decidedly bleached by the alcohol in which the 

 (old) material was immersed for a long period 

 before it was made the subject of that naked- 

 eye examination that led to the original 

 error of observation. 



The pecten varies in shape and size, as well 

 as in the number and the character of the 

 folds of tissue that compose it, according to 

 the genus to which the bird belongs. Indeed, 

 such a striking and varied picture does the 

 pecten exhibit, both when seen with the oph- 

 thalmoscope during life and in prepared mac- 



roscopical and microscopical specimens after 

 death, that one might almost recognize the spe- 

 cies by studying this organ and its relations to 

 other parts of a bird's fundus. In the accom- 

 panying text are a number of drawings of the 

 avian pecten as seen in prepared eyeballs. 



That the human hyaloid artery of fetal life 

 is a vestigal pecten seems almost self-evident. 

 No one who has examined a persistent hyaloid 

 artery and its branches, particularly if he has 

 been fortunate enough to see the vessels 

 carrying blood to and from their termination 

 in the vitreous, can fail to be reminded of the 

 structures that occur normally in some mam- 

 malian, most reptilian, and all avian eyes. 

 This arrangement surely carries us back in 

 fetal evolution to those sauropsidian ances- 

 tors who have left their mark on our em- 

 bryology. 



Attention may be especially drawn to the 

 pecten of the American Coot (Fulica ameri- 

 cana), consisting of 15 double folds. It shows 

 in a remarkable and unusual fashion their 

 fan-like arrangement, especially at the free, 

 upper margin of the organ; it is there firmly 

 attached to the fine vitreous processes and 

 the hyaloid membrane. See Fig. 84. 



In Gadow's contribution to Bronn's Tier- 

 Reich a list of the number of convolutions in 

 certain Birds is given, and reference is made 

 to an attempted classification of Aves based 

 upon it. 



The optic disc, viewed macroscopically, is 

 generally seen as an oval, ovoid, sometimes 

 almost round, white or yellowish-white area 

 largely obscured by its union with the base of 

 the pecten. Its long diameter is generally 

 from two to three times its width. 



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