US-P16.001ab ।US-P16.001cd ॥
In plain words
Whatever is hard in the body is earth; whatever flows in it is water — so the teaching runs. Digestion comes from fire, movement from air, and the open room inside from ether.
Close to the Sanskrit
The hard constituent in the body is earthy; the fluid is held to be made of water. Digestion, movement, and inner space would be what arise from fire, air, and ether.