Palmaris longus is a muscle that is missing in about 14% of the population. It originates on the medial epicondyle of the humerus through the common flexor tendon, and inserts into the palmar fascia.
The palmaris longus is a weak flexor of the wrist. There are other more powerful wrist flexors, so the palmaris longus tendon is used by surgeons if a tendon graft is needed elsewhere.
The other muscle I mention in this video is Pyramidalis, which is absent in about 20% of the population. Pyramidalis goes from the pubic bone to the linea alba, and works to tense the linea alba.