The arrangement of bones in the upper and lower limbs is almost identical, except for the bone located in the knee. Which bone is this?

The patella, or kneecap, is the bone located at the knee. It has no matching bone in the upper limb, whose corresponding joints do not have a kneecap. The femur is the thigh bone, while the ulna and clavicle are found in the upper limb.

AI-written and checked against the verified answer.