It was dim- lighted; but his eyes had never had to adjust themselves to any other light.

His world was very small.

Its limits were the walls of the lair; but as he had no knowledge of the wide world outside, he was never oppressed by the narrow confines of his existence.
But he had early discovered that one wall of his world was different from the rest.

This was the mouth of the cave and the source of light.

He had discovered that it was different from the other walls long before he had any thoughts of his own, any conscious volitions.