At last he found himself before the creature's gigantic and repulsive head which lay limp over a blood bathed stone, huge jaws partially open, and serrated rows of wicked, stiletto-sharp teeth gleaming yellowly in the flashlight's rays. The head in shape was bullet-like, ending in a blunt nose as big as a bushel basket and in two prominent nostrils. The green, lidless eyes were still open, shining faintly, and seemed to follow his movements, but the steaming blood poured with the force of a small hose from between triple row of bayonetlike teeth that curved inward like those of a shark, to splash and bubble freely to the rock floor and to dribble horribly over the warty, gray hide. Then Nelson discovered an amazing fact. About the great scaly neck, thick as a boy's waist, was fastened a ponderous collar, set with short, sharp spikes. Nelson gasped. "What in hell!" he cried. "This damn thing's somebody's property!" His mind, staggered at the thought of dealing with a race that could and would domesticate such a hideous monster. "Well, it's no use standing here," he muttered, wiping the sweat from his eyes. "This isn't getting poor Alden away from those devils." _Thud! thud!_ In the act of turning he paused, listened once more. Then he discovered to his amazement that the heart of the apparently dead reptile was still beating strongly. He could even see the yellow skin of its belly rise and fall. The effect was grotesque, uncanny. "Of course," muttered the shaken aviator, "I'd forgotten a reptile's ganglions will keep on beating for hours, like that shark we killed off Paumotu. Its heart didn't stop for five hours." * * * * * Leaving the slain allosaurus behind, the aviator limped onwards, doggedly following a trail which wound down, ever onwards, into the depths of the earth. Gradually the air became so filled with steam that he stripped off his fur jumper and trousers. Clad in a khaki flannel shirt, serge trousers and shoepacks, he paused long enough to count his cartridges, and found there were just fourteen. Hell! Not very many with which to venture into an unknown abyss. He distributed them in his pockets, and, somewhat relieved of the weight of the fur suit, took up his advance, playing the flashlight ahead of him as he went. "Poor Alden," he thought. "I wonder if he's still alive?" Every moment expecting to stumble over the mangled corpse of his friend he hurried on, making better time over the cavern floor, but soon even the lighter clothing commenced to feel oppressive. "Must be the earth's heat," he muttered, while the steam clouds rolled by him like ghostly serpents. "Guess the crust is very thin here--something like Yellowstone. Probably I'll find some thermal springs ahead."