瑜伽論記 24.182

24.182

第七解德，言當知欲界，如皮等者，謂以人身喻於三界，欲界如皮，上界似肉，無明在肉如血，以三界身中無明血等淋漏故也。

Seventh, explaining virtues: regarding the statement that one should know the desire realm is like skin, and so forth, it means using the human body as an analogy for the three realms: the desire realm is like skin, the higher realms are like flesh, and ignorance is in the flesh like blood, because within the body of the three realms, the blood of ignorance and so forth oozes and leaks out.