as complete as the others.” Cuvier further observes that whilst the branchiæ subsist, the aorta, in coming from the heart, is divided into as many branches on each side as there are branchiæ. The blood of the branchiæ returns by the veins, which unite towards the back in a single arterial trunk, as in the fishes; it is from this trunk, or immediately from the veins which form it, that the greatest part of the arteries which nourish the body, and even those which conduct the blood for respiration in the lung, spring. But
SKELETON OF SIREN.
in the species which lose their branchiæ naturally, the branches which go there become obliterated, except two which unite in a dorsal artery, and of which each gives off a small branch to the lung. “It is,” adds this eminent comparative anatomist, “the circulation of a fish metamorphosed into the circulation of a reptile.”
The same author observes that it had been objected that it would be impossible for these
