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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 only movements permitted in the joints of the digits are flexion and extension; these movements are more extensive between the first and second phalanges than between the second and third. The flexor hallucis longus and flexor digitorum longus flex the interphalangeal joint of the big toe and lateral four toes, respectively.
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.
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.
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 formula for the phalanges of the hand is 1-2-3-0-0 or 2-3-3-0-0 — or 0-1-2-3-0/0-2-2-3-0 if the three fingers of the hand are interpreted as the second, third and fourth. The upper phalanges of the second and third (or third and fourth) finger are elongated with more than 75% of the length of the corresponding metacarpal.
This includes the first phalanx of the first finger of the left hand, the first and second phalanx of the third right finger, the lower ends of the second, third and fourth metatarsals, the first and second phalanx of the second toe, the second and third phalanges of the third toe, the first, third and fourth phalanx of the fourth toe, the ...