792 THE AMERICAN NATURALIST. [VoL. XXXIV, 
vertebral centra, the numerous caudal vertebra. As regards 
the ribs, Pycraft considers it unsafe to infer that they lack 
uncinate processes, since these would be readily macerated 
off; the cervical ribs were slender and movably articulated. 
Abdominal ribs appear to 
have been present, as in 
the Crocodilia and Progano- 
sauria. 
In connection with the 
clawed quadrupedal stage in 
the history of birds, Opis- 
thocomus, the Hoactzin, 
proves to be of exceptional 
interest, ‘for,’ as Pycraft 
remarks, “it is probable 
R. 
f Ponens Right pes, x 1. After Bau 
Fic. 10. lura eig A, right manus, x 8, from Headley, after Dames ; B, right pes, 
Owen. 
T tibia ; Fb, fibula; R, radius; U, ulna; 7-7, metacarpals and metatarsals. 
that the peculiar habits of the nestling may be a survival of 
an order of HUE handed down from the very dawn of avian 
development." The young are reared in trees and at an early 
age climb out of the nest ; the hand is considerably longer than 
the forearm ; the pollex (I) is especially long and provided with 
a large claw; index II has an equally large claw, which is 
