This will avoid twisting the wrists out of alignment (ulnar/radial deviation, dorsiflexion) or curling the fingers excessively (antagonistic flexion/extension).
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In a properly coordinated technique, a relationship exists between the lifting/dropping (flexion/extension) of the fingers, and the rotational movement (pronation/supination) of the forearm.
There is a single foramen on the dorsal side of the tarsometatarsus, with a plantar exit hole between the third and fourth metacarpal's distal ends (presumably for the outer toe's adductor tendon) and another (presumably for nerves and blood vessels) on the plantar surface of the tarsometatarsus.
The unwanted material is periodically ejected (usually through the inhalant siphon or aperture) by contractions of the adductor muscles, which "clap" the shells together, pushing most of the water out of the mantle cavity and forcibly ejecting both the feces and the pseudofeces.
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Thanks to the well-preserved Ptilodus specimens found in the Bighorn Basin, Wyoming, we know that these multituberculates were able to abduct and adduct their big toes, and thus that their foot mobility was similar to that of modern squirrels, which descend trees head first.