MAMMALIA, 359 
in clinging that it serves the purpose of a fifth hand (Fig. 
378). The red-faced spider-monkey (Aves) is one of the 
most remarkable for the attenuation of its form. The tail 
is extremely long and bare upon its under surface, and 
with it they swing from limb to limb with the greatest ease. 
In walking upright, the arms are often held high in air, 
and the long tail curled over the head. The horned 
monkeys (Cedus), the bearded saki (P2thecta), and the 
howling monkeys (/ycefes), are familiar forms, The voice 
of the latter is so powerful that it can be heard a mile, the 
hyoid apparatus and windpipe (larynx) being wonderfully 
modified into a sound-producer, thesbody of the former 
assuming the functions of a large bony drum or air-sac 
connecting with the larynx. In the male these curious 
vocal organs are one third larger than in the female. Fol- 
lowing are the Cercopithecide, a group of monkeys peculiar 
to the Old World. The face of the dog-faced apes is pro- 
duced into a dog-like snout, more or less blunt or truncat- 
ed; the eyes are small, deeply set, and placed close to- 
gether. The wanderoo (A@acacus), the Gibraltar monkey 
(Macacus inuus), the mandrill and chacma, and the bab- 
boon (Cynocephalus), are familiar forms. Allied are the 
Sleepers (Semnopithecide), of Africa and Asia, 
Apes (Simiide).—The animals of this family in their 
physical development show a near approach to the human 
type. Their position is nearly erect, the tail absent, and 
the arms are much longer than the legs. The gibbons 
(Fig. 379) (Aylobates) attain a length of three feet. In the 
siamang, when standing erect, the fingers drag upon the 
ground, the limbs being used to swing them through the 
trees ; the thumbs and great toes only have nails. In color 
they are black, the hair being long, coarse, and glossy. 
They live in troops in the forests of Java, Borneo, etc., 
and are generally led by a chief, who gives warning at the 
approach of danger. The females show great solicitude 
for their young, and when in danger give vent to loud cries 
