National Geographic : 1940 Aug
The Manlike Apes of Jungle and Mountain @ National Geographic Society Painting by Elie Cheverlange Throat Sac Inflated, the Siamang Is Ready to Scream-or Yawn! Usually at sunrise and sunset. Siamang Gibbons exercise their powerful voices. Often the shrieks may be heard a mile off. These largest members of the gibbon family dwell in Sumatra and the Malay Peninsula.