It is taught: What is the form of the fetus? At the beginning of its formation it is similar to a grasshopper. Its two eyes are like two drops, [like the eyes] of a fly. Its two nostrils are like two drops of a fly, and its two ears are like two drops of a fly.
Its two arms are like two threads of crimson wool. Its mouth is like a grain of barley. Its member is like a lentil and the rest of its limbs are connected to it like an unshaped mass. In its regard it says: “You saw my unshaped mass” (Psalms 139:16).
If it is a female, it is split lengthwise like a lentil. It does not have differentiation of arms and legs. How is the fetus situated in its mother’s womb? It is folded and placed like a ledger, its head lies between its knees, its two hands on its two temples, its two heels on its two buttocks, its mouth is closed, its navel is open, and it eats of what its mother eats, and it drinks of what its mother drinks.
It does not produce waste lest it kill its mother. When it emerges into the air of the world, what was closed is opened and what was open is closed.