Mandrill, (Mandrillus sphinx), colourful and primarily ground-dwelling monkey that inhabits the rainforests of equatorial Africa from the Sanaga River (Cameroon) southward to the Congo River. The mandrill is stout-bodied and has a short tail, prominent brow ridges, and small, close-set, sunken eyes. The adult male has bare coloured patches of skin on both the face and the buttocks. On the face the cheeks are ribbed and range in colour from bright blue to violet, with scarlet along the bridge and end of the nose. The buttock pads are pink to crimson, shading to bluish at the sides. The long body fur is olive to brown, and the small beard and the neck fur are yellow; the eyes are framed in black. The adult male is about 90 cm (3 feet) long, including the tail stub, and weighs up to 35 kg (77 pounds), which makes it the largest of all Old World monkeys. The female, also with bare face and buttocks, is duller in colour and considerably smaller, only about 13 kg (29 pounds) on average. Like baboons, females develop swellings on their hindquarters when they are in estrus.