The structure labelled II articulates with III to form

The structure labelled II articulates with III to form a hinge joint. A joint is where two bones come together, and the type of joint depends on the way the bones are able to move in relation to each other. A hinge joint allows for movement in one direction, like a door hinge. It is composed of two bones that fit together and move along a single axis. Structure II is likely referring to a bone that has a convex, rounded end, while structure III is a bone that has a concave, curved surface. When these two bones come together, they form a hinge joint that allows for movement in one direction only, such as the elbow or knee joint. In contrast, a sliding joint allows bones to glide past each other, a pivot joint allows for rotation around a single axis, and a ball-and-socket joint allows for movement in multiple directions.