The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it. Jaws are used for biting, chewing, and handling food and work by moving in opposition to one another. The mandible is made up of a horizontal arch that houses blood vessels and nerves and holds the teeth. Two vertical pieces on either side of the skull provide adjustable hinge joints. Additionally, the jaw serves as an attachment point for chewing-related muscles.