1st carpo-metacarpal joint is
a) Saddle joint
b) Ball and socket joint
c) Secondary cartilaginous joint
d) Hinge joint
First carpo-metacarpal joint is only carpo-metacarpal joint which has a separate joint cavity. Movements at this joint are, therefore; much more free than at any other corresponding joint.
Saddle variety of synovial joint (because the articular surfaces are concavo-convex)