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B. NATURAL HISTORY. 
Bluebird, Sialiajialis. 
Chipping Sparrow, Spizella socialis. 
Yellow Warbler, Dendroica cestiva. 
Wilson’s Thrush, Turdus juscescens, and the 
Spotted Sand-piper, Tringoides macularius. 
In these he had found three distinct tarsal bones, — two in the 
proximal senes answering to the astragalus and calcaneum or the 
tibicde and fibulare of Gegenbaur, and one in the distal series rep¬ 
resenting the centrale. 
The first two anchylose at an early stage, and present an hour¬ 
glass-faced articular surface, as described in the astragalus of Loe- 
laps by Professor Cope. The final anchylosis of these conjoined 
ossicles with the tibia formed the bicondylar trochlea so peculiar 
to the distal end of a bird’s tibia. 
The distal tarsal ossicle became united with the proximal ends 
of the metatarsals as Gegenbaur had shown. 
In the carpus he had found four perfectly distinct ossicles, — two 
in the proximal series, and two in the distal series; the bones of 
the proximal series remaining free, while the bones of the distal 
series unite with the base of the mid and outer metacarpal. 
Thus we have in the wing, as in the leg, the joint between the 
first and second carpal scries. 
In the Kingbird and Yellow Warbler he had found a fifth car- 
pal on the radial side. 
2. On the Mechanism of Flexion and Extension in Birds’ 
Wings. By Elliott Coues, of Fort McHenry, Maryland. 
I desire to bring to the notice of the Association, and of orni¬ 
thologists in general, a certain mechanism in the wings of birds, 
which has not received the attention that is warranted by its inter¬ 
est and importance. No discovery is claimed; for probably the 
point cannot have been overlooked : nevertheless, having seen no 
account of it, I am led to believe that it will be new to many, as 
it was to myself when I first detected it. 
I will first briefly recapitulate the well-known points of osseous 
