Bašmu, inscribed in cuneiform as MUŠ.ŠÀ.TÙR/TUR, “Venomous Snake,” was an ancient Mesopotamian mythological creature, a horned snake with two forelegs and wings and the Akkadian word for the constellation Hydra (the snake), abbreviated to dMUŠ. The Sumerian terms ušum (portrayed with feet) and muš-šà-tùr “birth goddess snake” (without feet) may represent differing iconographic types and possibly different demons. It first appeared in the 22nd century BC, in a cylinder inscription of Gudea.
In the Angim, or "Ninurta's return to Nippur," it was identified as one of the eleven ur-sag, “warriors,” defeated by Ninurta. Bašmu was created in the sea and was “sixty double-miles long,” according to a fragmentary Assyrian myth which recounts that it devoured fishes, birds, wild asses and men, securing the disapproval of the gods who sent Nergal/Palil, the “snake charmer’” to vanquish it. It was one of the eleven monsters created by Tiāmat in the Epic of Creation, Enûma Eliš. It had "six mouths, seven tongues and seven . . .-s on its belly."
MUL.APIN has a "serpent" constellation (MUL.DINGIR.MUŠ) which loosely corresponds to Hydra.