448 Prof. Carl Vogt on 
in the Dinosaurs, in Archeopteryx, and in Birds, is therefore 
independent of the power of flight, and only relates to that 
of supporting the body on the hind-feet alone. 
Now I believe I have shown in the above-mentioned article 
that all the characters whereon are based the consideration of 
Dinosaurs to be regarded as the ancestors of Birds are only 
related to the development of the power of keeping an upright 
position upon the hind-feet. Thanks especially to the labours 
of American naturalists, we now know that the feet of the Din- 
esaurs had but three digits, with the indication, sometimes, 
of a fourth; also that these animals walked upright, as shown 
by their numerous foot-prints, formerly attributed to Birds, 
and that their pelvis resembled that of Birds. On these 
principles they had then a resemblance to Birds and to the 
Archeopteryz ; but the known skeleton of Compsognathus and 
other recognized facts show us that this development of the 
hind-feet was combined, as in the Mammals that leap, with a 
more or less considerable shortening of the fore-feet, which 
is in direct contradiction to the adaptation for flight, demand- 
ing, as that does, an elongation of the fore limb. Certain 
Dinosaurs, perhaps, perched like the Archeopteryx and Birds ; 
but they were not more in the road to adaptation for flight 
than are the Tree-kangaroos of the New-Guinea forests (Den- 
drolagus), which also perch, in spite of their feet being 
adapted to leaping. 
As to the adaptation for flight, we see it act in two direc- 
tions, wholly distinct, according as the surface opposed to the 
air is formed by an extended membrane or by feathers. The 
manus of Pterosaurs and Bats obeys the mechanical condi- 
tions of the extended membrane, that of Birds is modified 
with a view to the remiges. These are, especially, the forms 
of manus which show the fundamental differences arising 
from different mechanical conditions 
The shoulder-girdle in all flying animals exhibits a con- 
struction fit to ensure great fixity, united with considerable 
mobility, but limited as to the extent of movement. This fixity 
is due, in the first place, to the development of the coracoid, 
and, secondly, to that of the scapulze and the clavicles. The 
