Final answer:
The depression on the posterior surface of the humerus is the olecranon fossa. It is designed to accommodate the olecranon process of the ulna during full elbow extension, differentiating it from the medial epicondyle, which is not a depression but an attachment point for muscles.
Step-by-step explanation:
The depression found on the posterior surface of the humerus is the olecranon fossa. This large depression is crucial as it accommodates the olecranon process of the ulna when the elbow is fully extended. The medial epicondyle is a different feature of the humerus, which serves as an attachment point for muscles but is not the depression that receives part of the ulna.
The distal end of the humerus features two fossae on the anterior surface, the coronoid fossa and the radial fossa, which receive the coronoid process of the ulna and the head of the radius, respectively, when the elbow is flexed. However, posteriorly, it is the olecranon fossa that interacts with the ulna. This understanding is essential for comprehending the functionality of the elbow joint in terms of bone structure and muscle attachment, facilitating movements of the forearm.