Insertion: By four tendons, each penetrating a membranous expansion of the dorsum of the second to fifth digits and dividing over the proximal phalanx into a medial and two lateral bands. The medial band inserts into the base of the middle phalanx while the lateral bands reunite over the middle phalanx and insert into the base of the distal phalanx.

Innervation: Radial, C6, 7, 8

Action: Extends the MCP joints and, in conjunction with the lumbricals and interossei, extends the IP joints of the second through fifth digits. Assists in abduction of the index, ring, and little fingers; and assists in extension and abduction of the wrist

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