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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 ...
Joints of the hand, X-ray Interphalangeal ligaments and phalanges. Right hand. Deep dissection. Posterior (dorsal) view. The PIP joint exhibits great lateral stability. Its transverse diameter is greater than its antero-posterior diameter and its thick collateral ligaments are tight in all positions during flexion, contrary to those in the metacarpophalangeal joint.
The second, third, and fourth dorsal interossei have insertions both proximally on the base of the metacarpal and hood, and distally on the lateral bands and central tendon of the extensor mechanism. The abductor digiti minimi, effectively the "fifth dorsal interosseus" or the dorsal interosseus of the little finger, has only a proximal insertion.
These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the proximal phalanges. [1] Being condyloid, they allow the movements of flexion , extension , abduction , adduction and circumduction (see anatomical terms of motion ) at the joint.
The fourth and fifth metacarpal bones are commonly "blunted" or shortened, in pseudohypoparathyroidism and pseudopseudohypoparathyroidism. A blunted fourth metacarpal, with normal fifth metacarpal, can signify Turner syndrome. Blunted metacarpals (particularly the fourth metacarpal) are a symptom of nevoid basal-cell carcinoma syndrome.
The metatarsal bones or metatarsus (pl.: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges . Lacking individual names, the metatarsal bones are numbered from the medial side (the side of the great toe ): the first , second , third , fourth , and fifth ...
The two heads of each muscle form a central tendon which passes forwards deep to the deep transverse metatarsal ligament. [1] The tendons are inserted on the bases of the second, third, and fourth proximal phalanges [2] and into the aponeurosis of the tendons of the extensor digitorum longus [3] without attaching to the extensor hoods of the toes.
Extensor digitorum brevis extends the first four digits at the metatarsophalangeal joint and assists in extending the second, third and fourth digits at the interphalangeal joint. The fifth digit, lacking any insertion from extensor digitorum brevis, can only be raised by the long extensor.