The Descent of Man

(69. Owen, 'Anatomy of Vertebrates,' vol. iii. p.
71.) Their hands, however, are admirably adapted
for climbing trees. Monkeys seize thin
branches or ropes, with the thumb on one side
and the fingers and palm on the other, in the
same manner as we do. They can thus also lift
rather large objects, such as the neck of a bottle,
to their mouths. Baboons turn over stones, and
scratch up roots with their hands. They seize
nuts, insects, or other small objects with the
thumb in opposition to the fingers, and no
doubt they thus extract eggs and young from
the nests of birds. American monkeys beat the
wild oranges on the branches until the rind is
cracked, and then tear it off with the fingers of
the two hands. In a wild state they break open
hard fruits with stones. Other monkeys open
mussel-shells with the two thumbs. With their
fingers they pull out thorns and burs, and hunt
for each other's parasites. They roll down stones,
or throw them at their enemies: nevertheless,
they are clumsy in these various actions,