The first one differs from the rest in being a hinge-joint; the others are modified ball-and-socket, so that movement takes place round two axes:
Transverse - flexion and extension.
Antero-posterior - abduction and adduction.
Fig. 10. - Muscles of the Hand (Palmar Aspect).
A capsule completely surrounds each joint, which is very much weaker on the dorsal surface, where the joint is strengthened by the expansion of the extensor tendon.
Ulnar and Radial Lateral ligaments, strong cord-like bands attached to the tubercles on the sides of the heads of the metacarpal bones and the bases of the phalanges.
The Palmar ligaments are plates of fibro-cartilage attached firmly to the phalanges, but only loosely to the metacarpals, so that during movements of the joints they can glide up and, down. In this plate two sesamoid bones are developed in the thumb, and one on the radial side of the forefinger.
Synovial membrane lines the capsule of each joint.
Transverse Metacarpal ligament consists of bands of transverse fibres, which connect the palmar ligaments of the four inner metacarpo-phalangeal joints. This binds together the distal extremities of the bones.