Dorsal interossei of the foot Dorsal interossei of the foot In human anatomy, the dorsal interossei of the foot are four muscles situated between the metatarsal bones. The four interossei muscles are bipenniform muscles each originating by two heads from the proximal half of the sides of adjacent metatarsal bones. The two heads of each muscle form a central tendon which passes forwards deep to the deep transverse metatarsal ligament. The tendons are inserted on the bases of the second, third, and fourth proximal phalanges and into the aponeurosis of the tendons of the extensor digitorum longus without attaching to the extensor hoods of the
Phalanx bone terminal phalanges and fused metacarpal bones able to absorb the stress from running. The sloth spends its life hanging upside-down from branches, and has highly specialized third and fourth digits for the purpose. They have short and squat proximal phalanges with much longer terminal phalanges. They have vestigial second and fifth metacarpals, and their palm extends to the distal interphalangeal joints. The arboreal specialization of these terminal phalanges makes it impossible for the sloth to walk on the ground where the animal has to drag its body with its claws. Phalanx bone The phalanges (singular: "phalanx" ) are digital bones