258 ANIMAL PHYSIOLOGY. 
sum crowds on the venous blood and passes itself with some of 
the darker blood into the aortic vessels, in which the arrange- 
Fig. 237. 
Fic. 236.—Heart and arteries of a turtle (Chelydra). rp, right pulmonary, and lp, left pul- 
Leh artery ; other letters the same signification as in the previous figure (after Gegen- 
aur). 
Fic. 237._Heart of a turtle (Chelone midas). A. Drawing from nature, the ventral face of 
the ventricle being laid open. B. Diagram explanatory of the circulation. Everywhere 
the arrows indicate the course the blood takes. FR. A., L.A., right and left auricles. 
v, the right, v’, the left median auriculo-ventricular valves. C.v, cavum venosum. C.p, 
cavum pulmonale. a, the incomplete ee which divides the cavum pulmonale from 
the rest of the cavity of the ventricle. P..A, pulmonary artery. R&R. Ao, L. Ao, right and 
left aortas (after Huxley). 
ment of the valves assists materially. Note that, as the systole 
advances, the imperfect septum between the cavum pulmonum 
and cavum venosum approaches the back of the heart wall, and 
thus tends to shut off the cavum pulmone from the purer blood. 
As a result of the entire arrangement, the least oxidized 
blood passes to the lungs, and the most aérated to the head and 
anterior parts of the animal. 
In the frog and other creatures, with three imperfectly sepa- 
rated heart cavities, a similar result is attained. 
The resemblances in such cases to the foetal conditions in 
mamuals, including man, will be apparent, and it is especially 
