The muscle highlighted is the quadratus plantae muscle of the foot.

The intrinsic muscles on the plantar aspect of the foot are divided into four layers. The quadratus plantae muscle is found in the second layer of muscles. There are two muscles in the second layer:

• Quadratus plantae
• Lumbricals

The muscles in the second layer are associated with the tendons of the flexor digitorum longus muscle. This tendon forms the site of insertion for the quadratus plantae muscle, and forms the site of origin for the four lumbricals. The quadratus plantae muscle has two heads – a medial head and a lateral head.

Origin: Medial surface of calcaneus and lateral process of calcaneal tuberosity

Insertion: Lateral aspect of flexor digitorum longus tendon.

Innervation: Lateral plantar nerve

Action: Flexion of toes 2-5 (assists the action of flexor digitorum longus)

Learn more about the anatomy of the muscles of the foot in this tutorial.