On the dorsal aspect of one finger, clean the extensor expansion and identify the extensor tendons which attach to it (Figure 9.3).
On the dorsum of the metacarpophalangeal (m/p) joints, each tendon of the extensor digitorum muscle spreads into a fibrous extensor expansion. The extensor expansion covers the dorsum of the proximal phalanx. Distally, the expansion divides into a central slip which inserts into the middle phalanx and two lateral slips which insert into the terminal phalanx (Figure 9.4).Clean the tendon of an interosseous muscle and identify its attachments to the base of the proximal phalanx and the extensor expansion. On the palmar surface of a finger, clean the distal portion of the associated lumbrical muscle and identify its attachments to the tendon of flexor digitorum profundus muscle and the lateral (radial) side of the extensor expansion.
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