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The thumb contrasts with each of the other four fingers by being the only one that: Is opposable to the other four fingers; Has two phalanges rather than three. However, recently there have been reports that the thumb, like other fingers, has three phalanges, but lacks a metacarpal bone. [3]
Opposable thumbs enable humans to do tasks that most animals can’t even attempt – from eating food easily to driving a car. You may not realize that we are not alone with our amazing thumbs ...
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.
A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs.A few other vertebrates such as the koala (which has two opposable thumbs on each "hand" and fingerprints extremely similar to human fingerprints) are often described as having "hands" instead of paws on their front limbs.
A bear's hand lacks the opposable thumb possessed by humans and various primates that enables the grasping and handling of objects using the fingers. The false thumb serves a similar function.
Opossums and their Australasian cousins have evolved an opposable thumb, a feature which is also commonly found in the non-related primates. [18] The marsupial moles have many resemblances to the placental talpid moles and golden moles. [19] [20] Marsupial mulgaras have many resemblances to placental mice. [21] Planigale has many resemblances ...
Generally, triphalangeal thumbs are non-opposable. In contrast to most people with opposable thumbs, a person suffering from TPT cannot easily place his or her thumb opposite the other four digits of the same hand. The opposable thumb's ability to effortlessly utilize fingers in a "pinch" formation is critical in precision gripping.
Modern humans are unique in the musculature of the forearm and hand, though opposable thumbs or structures like them have arisen in a few animals. In dinosaurs, a primitive autonomization of the first carpometacarpal joint (CMC) may have occurred. In primates, a real differentiation appeared perhaps 70 mya, while the shape of the human thumb ...