The tentorium (plural tentoria) is a term use to refer to the framework of internal supports (a false endoskeleton) within an arthropod head. The tentorium is formed by ingrowths of the exoskeleton, called apophyses, which fuse in various ways to provide rigid support for the muscles of the head (particularly those associated with the mouthparts) and additional protection for the brain and other neural structures. The arthropod head is therefore generally the part of the body that is least prone to distortion.