go The Bird 
bone extending backward from the thigh-socket, sepa- 
rated from the ischium 
(except at the extreme 
end) by a long open slit. 
In other animals these 
bones are as different in 
shape as can be imagined, 
but, almost without excep- 
tion, the position of each 
is relatively thesame. The 
extreme extension, forward 
and back, of the ilium 
above the back-bone, thus 
joining with more vertebre, 
is directly connected with 
two-legged erect locomo- 
tion. A parallel condition 
is found in some Dinosaurs 
—those extinct giant rep- 
tiles — certain of which 
Fic. 64.—Pelvie arch of an embryo bird, 
to show similarity of the two as walked more or less on 
contrasted with Fig. €5 
their hind legs. 
Another fundamental 
resemblance is found be- 
tween the thigh-girdles of 
Dinosaurs and other rep- 
tiles and that of a bird in 
Fic. 65.—Pelvie arch of an adult bird. re mre 
(fhe three figures by courtesy of the ese. As is shown in 
ee Eee Figs. 63-65, the pubis slants 
slightly forward in both reptile and embryo bird; but in 
