Final answer:
Biaxial joints with oval convex surfaces that fit into complementary depressions are either condyloid joints or saddle joints, allowing movement along two axes, as seen in the wrists, fingers, and the base of the thumb.
Step-by-step explanation:
The student is asking about biaxial joints that are characterized by an oval convex surface on one bone that fits into a complementary shaped depression on the other. These are known as condyloid joints (also referred to as ellipsoidal joints) and saddle joints. Condyloid joints allow for angular movement along two axes, such as in the wrist and fingers, which can move side to side and up and down. Examples include the metacarpophalangeal joints of the hand and the radiocarpal joint of the wrist.
Saddle joints also permit movement along two axes and have articulating surfaces that are saddle-shaped, being concave in one direction and convex in the other. An example of a saddle joint is the first carpometacarpal joint located at the base of the thumb, which allows for the thumb to move away from the palm along two planes. This joint is what gives humans their distinctive opposable thumbs, enabling a wide range of thumb movements.