The quadratus plantae muscle helps flex the small toes since it corrects the flexor tendon’s oblique vector when it crosses the foot’s plantar surface. This, unlike many of the other muscles in the foot, doesn’t have a homolog in the hand.
It comes from two heads. The larger (or medial) head is muscular and attaches to the calcaneus’ medial concave surface. The other, lateral head is tendinous and flat. It stems from the calcaneus’ inferior surface on the lateral border, ahead of its tuberosity’s lateral process and from the long plantar ligament. These two parts come together and terminate in a flat band. This band inserts into the lateral margin and beneath the flexor digitorum longus tendon’s surfaces. Here a groove is created and the tendon fits into it. The flexor digitorum longus tendons receive slips from it that go along to the second, third and fourth toes.