There are five, like five digits of your hand.
Place your thumb into your palm, then lay that hand palm down on your other arm.
Your 4 fingers now show distribution: spells PFPF [pass/fail, pass/fail]:
- Pronator teres
- Flexor carpi radialis
- Palmaris longus
- Flexor carpi ulnaris
Your thumb below your 4 fingers shows the muscle which is deep to the other four:
- Flexor digitorum superficialis.