An extensor expansion (extensor hood, dorsal expansion, dorsal hood, dorsal aponeurosis) is the special connective attachments by which the extensor tendons insert into the phalanges. These flattened tendons (aponeurosis) of extensor muscles span the proximal and middle phalanges. At the distal end of the metacarpal, the extensor tendon will expand to form a hood, which covers the back and sides of the head of the metacarpal and the proximal phalanx.