768 The American Naturalist. [September, 
regarding the Pterodactyls as widely removed from the birds 
is removed. 
Tue HOMOLOGIES or THE DIGITS. 
In the wing of the adult bird only three digits at most at- 
tain full development, and, since the birds have descended 
from pentadactyle forms, it becomes a matter of some import- 
ance to compare these three with those of the normal hand; 
in other words to ascertain which digits have been lost in the 
process of evolution. Naturally many attempts have been 
made to solve the problems involved, and within the last 
decade four different views have had their advocates, though 
naturally some of these ideas of homology date back to a 
more remote period. 
Thus Gegenbaur (’64), reasoning from the apparent ten- 
dency towards reduction of the digital elements on the ulnar 
side of the crocodilian manus, concludes that the persistent 
digits of the bird wing are the I, II and III of the normal 
pentadactyle hand. In this he has had many followers, 
among them Rosenberg (’73), Huxley (’71), Jeffries (’81), 
Jackson (’88),and Parker (’88). For this view there are many 
more arguments than the one mentioned above, and Dr. Jef- 
fries has given an able summary of them. 
A second view is that of Owen, according to which the 
digits in question are II, III and IV. This is based partly 
(36) on the fact of the absence of the radial artery, which 
would indicate reduction on the radial side of the manus; and 
partly (62) on features supposed to exist in the British Museum 
specimen of Archeopteryx. In this there are apparently four 
digits present in connection with the right wing, but as these 
show considerable dislocation, one may, as suggested by Pro- 
fessor Owen, have belonged to the other side. This view has 
fewer supporters than the other, among them Morse and Coues. 
Morse (’72) contributes not a little in support by his advocacy 
of the law of digital reduction asa valid argument in this 
connection. That Coues supports the same view I take partly 
on the statement of others and partly from the fact that, while 
in the text of his “ Key " ('87), he gives both views, the num- 
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