The dorsal interossei are four small deep muscles of the hand. They are spindle-shaped and bipennate, lying in the interosseous spaces, between the metacarpal bones, on the dorsal aspect of hand. Each one of them arises by two heads from the adjacent sides of the bases of the next two metacarpal bones.
The first dorsal interosseous muscle originates from the inner surfaces of the first (thumb) and second (index finger) metacarpal bone; it is inserted into the radial side of proximal phalanx of index finger. The second dorsal interosseous arises from the inner surfaces of the second (ulna side) and third (radial side) metacarpal bone and is inserted into the radial side of middle finger proximal phalanx. The third and fourth dorsal interossei originate from the inner surfaces of the third, fourth, and fifth metacarpal bone and are inserted into the ulnar side of the middle and ring fingers.
Action
The these small muscles pull the proximal phalanges of the index, middle, and ring finger towards the palm of hand.
Innervation
They are supplied by motor nerve fibers springing from the ulnar nerve, which originates from the brachial plexus, from C8-T1).
Blood Supply
They are irrigated by secondary arterial branches arising from the deep palmar arch.
Below, the dorsal interossei muscles
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