Siamangs' hands are very much like ours; they have four long fingers plus a smaller opposable thumb. Their feet have five toes, including an opposable big toe. Siamangs can grasp and carry things with both their hands and their feet. When they swing through the trees (called brachiating), they use four fingers of their hands like a hook.So, they need long arms to grab the branches when they jump from a tree to another.