Final answer:
The superficial layer of flexor forearm muscles originates from the medial epicondyle of the humerus, forming the common flexor tendon.
Step-by-step explanation:
The superficial layer of the flexor forearm muscles, such as the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor digitorum superficialis, originates from the medial epicondyle of the humerus. This common tendon is known as the common flexor tendon. Due to the powerful grasping function of these muscles, the medial epicondyle is larger and more robust compared to the lateral epicondyle, which gives origin to the comparatively weaker posterior forearm muscles.