section_path: Anatomy and physiology/Body
section_name: Body
paragraph_text: Body
  
  Primates generally have five digits on each limb (pentadactyly), with a characteristic type of keratin fingernail on the end of each finger and toe. The bottom sides of the hands and feet have sensitive pads on the fingertips. Most have opposable thumbs, a characteristic primate feature most developed in humans, though not limited to this order (opossums and koalas, for example, also have them). Thumbs allow some species to use tools. In primates, the combination of opposing thumbs, short fingernails (rather than claws) and long, inward-closing fingers is a relict of the ancestral practice of gripping branches, and has, in part, allowed some species to develop brachiation (swinging by the arms from tree limb to tree limb) as a significant means of locomotion. Prosimians have clawlike nails on the second toe of each foot, called toilet-claws, which they use for grooming.
  
  The primate collar bone is a prominent element of the pectoral girdle; this allows the shoulder joint broad mobility. Compared to Old World monkeys, apes have more mobile shoulder joints and arms due to the dorsal position of the scapula, broad ribcages that are flatter front-to-back, a shorter, less mobile spine, and with lower vertebrae greatly reduced - resulting in tail loss in some species. Prehensile tails are found in the New World atelids, including the howler, spider, woolly spider, woolly monkeys; and in capuchins. Male primates have a low-hanging penis and testes descended into a scrotum.