The flexor digitorum brevis is a short, thick muscle located in the sole of foot, right under the plantar aponeurosis (deep fascia). It originates by a short strong tendon from the medial tubercle of the calcaneum bone and the plantar aponeurosis. Then it extends forwards, with the muscular belly ending up in four tendons, which are lodged in the synovial canal with the flexor digitorum longus tendons. Right in the region of the proximal phalanges of the lateral four toes, each of the four flexor digitorum brevis tendons splits into two slips that are inserted into the base of the middle phalanges of these toes.
Action/Function
This plantar muscle flexes the middle phalanges of the lateral four toes, closing them tightly. Although it is not as dexterous and practical as the flexor muscles of fingers and hand, it is very useful for neurologists when performing the Babinski reflex test on adults to see if there is a neurological degeneration or damage of spinal cord motor fibers; when it does not contract and the toes remain extended and open, then it is a sign that there is damage to spinal cord.
Innervation
The flexor digitorum brevis is innervated by branches of the medial plantar nerve, which originates from L5, S1 roots.
Blood Supply
It is supplied by arterial branches of the lateral and medial plantar artery, which arise from the posterior tibial artery.
Below, image of plantar (sole) surface of human foot, showing the flexor digitorum brevis muscle
