Concave Forms on the Skeleton
A trochlea (TROK-lee-uh) is a spool-shaped form. A trochlea is shaped to receive a convexity at a joint and allow movement only through one plane.
A facet (fa-SET) is a shallow depression that recieves the convexity of another bone at a joint.
A fossa (FOSS-uh) is a hollow that is deeper than a facet.
A foramen (fuh-RAY-men) is a hole.
A groove is exactly that, a thin, linear depression.