VII THE BIRD WITHIN THE EGG 285 
right ventricle and carries impure. Outside the heart 
the two arteries cross and there is a small passage 
from one to the other, so that the pure and impure 
blood are mixed. The fourth pair of arches have 
become separate except at this one »oint ; but what 
should have followed, has not—viz. the reduction of 
the right aorta to a rudimentary state. Otherwise 
the crocodile might have become a warm-blooded and 
altogether finer beast. 
SOME OF THE LITERATURE OF THE SUBJECT. 
(1) Foster and Balfour’s Elements of Embryology. 
(2) The article on “ Embryology” in Newton’s Dictionary of 
Birds, 
(3) Bronn’s Thzer-Reich, vol. “Aves.” [Dr. Gadow is the 
author of both 2 and 3.] 
(4) Duval’s Atlas Dembryologie. 
