A sagittal crest is a ridge of bone projecting up, from front to back, along the top midline of the skull. It serves as a muscle attachment area for the temparalis muscles that extend up both sides of the head from the mandible (jaw). The presence of a sagittal crest indicates that there are exceptionally strong jaw muscles. Some Australopithecus afarensis and the robust australopithecines (Australopithecus robustus, boisei, and aethiopicus) had sagittal crests. Among the living primates, the most prominent sagittal crests are found on adult male gorillas. Humans do not have them.