The flexor digitorum brevis muscle is located in the foot. Its precise location is within the sole of the foot, directly above the plantar aponeurosis, which supports the arch of the foot. It goes deep into the foot and only a very thin layer of fascia (connective tissue) divides it from the lateral plantar vessels.
The flexor digitorum brevis muscle originates in the calcaneus (heel bone) and the plantar fascia (the fascia in the sole of the foot). It then inserts into the middle phalanges, which are the middle bones of the second through fifth toes. It receives its nerve supply from a nerve called the medial plantar nerve.
This muscle enables the four lateral (outer) toes to be flexed. As the flexor digitorum brevis muscle moves forward, it divides into four separate tendons, so that each of the four lateral toes has its tendon. These tendons each divide at the base of the first phalanges, which are the backmost bones of the toes, in order to allow the tendon of the flexor digitorum longus to pass through. Later, the two slips of each tendon reunite and then divide a second time before inserting into the sides of the middle phalanges.