10 
/ 
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 ophthalmoscope during life and as prepared macroscopical 
and microscopical specimens after death, that one might almost 
recognize the species by studying this organ and its relations to 
other parts of the bird’s fundus. 
While there seems no doubt that the pecten carries the nutrient 
vessels of the retina, and probably of other intra-ocular structures, 
its erectile character and its capacity for being alternately filled 
with and emptied of considerable blood at short notice raises the 
presumption that it takes an essential part in the function of ac¬ 
commodation, probabl}^ as before stated, by pushing forward the 
lens by a sort of hydraulic pressure when it is filled with blood, 
and allowing it to recede when flaccid and empty. So far as I 
have noticed with the ophthalmoscope, although the free end of the 
pecten points toward the posterior surface of the lens, it is invari¬ 
ably found in the nasal half of the vitreous, and thus does not 
interfere with the passage of the light rays to the fovea or other 
visual areas. 
Slonaker, 5 6 whose macroscopical observations of the interior of 
hardened birds’ eyes have so far corresponded closely to the ophthal¬ 
moscopic view of the living fundi of birds’ eyes we have both exam¬ 
ined, has noticed that a line joining the visual area in birds with a 
single fovea and the optic papilla forms about a right angle with the 
pecten. 
That the hyaloid artery of fetal life is a vestigial 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 termina¬ 
tion in the vitreous, can fail to be reminded of the structures that 
occur normally in some mammalian, most reptilian, and all avian 
eyes. This arrangement surely carries us back in fetal evolution to 
those sauropsidian ancestors who have left their mark in our em¬ 
bryology. It is not improper for me to mention here the admirable 
anatomical description by Treacher Collins 0 of a case of persistent 
5. A Comparative Study of the Area of Acute Vision in Vertebrates Journal 
of Morphology, xiii. No. 3, p. 477. 
6. The Anatomy and Fathology of the Eye, The Lancet, Feb. 24, 1900. 
