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 first dorsal interosseous is also able to rotate the index finger slightly at the metacarpophalangeal joint and assist adductor pollicis in thumb adduction.

[5] All interossei pass dorsal to the transverse metacarpal ligament but slightly volar to the flexion-extension axes of rotation of the MP joints.

This IP extension is therefore stronger than MP abduction/adduction which is produced by continued action except for the index and little fingers.

[3] When the MP joints are flexed, the transverse metacarpal ligament enhances the function of the distal interossei by acting as a pulley and preventing them from becoming slack, further increasing the effectiveness of IP extension.

[6] This article incorporates text in the public domain from page 464 of the 20th edition of Gray's Anatomy (1918)