790 MAMMALIA. 
young birds, spiders, and insects. Their voice is powerful, and one 
species (the Siamang) has a laryngeal sac. As regards teeth, the 
gibbons are most like man. Some authorities rank the gibbons in a 
separate family apart from the three other Anthropoids. 
The Orangs (.S¢za) live in swampy forests in Sumatra and Borneo. 
The males measure over 4 ft. They walk on their knuckles and 
on the outer edges of the feet. The skull is prolonged into a vertical 
crest. There are but slight supra-orbital ridges. The canines are very 
large. There are twelve ribs as in man, and sixteen dorso-lumbar 
Fic. 419.—Skull of gorilla. 
vertebree. The larynx is connected with two large sacs which unite 
ventrally. They are arboreal in their habits, and make nests in the 
branches. They are exclusively vegetarian. As regards the structure 
of the brain, the Orangs are most like man. 
The Gorillas (Gorz//a) live in Western Equatorial Africa. They are 
larger than all other apes, and larger than man, though not over 54 ft. 
in height. The arms reach to the middle of the lower leg, and the 
animals walk with the backs of their closed hands and the flat soles ot 
their feet on the ground. There are prominent supra-orbital ridges. 
The canines of the males are very large. The cervical vertebra bear 
very high neural spines, on which are inserted the muscles which 
support the heavy skull. There are thirteen ribs, and seventeen 
