[TA] muscle of first layer of plantar muscles; origin, medial tubercle of calcaneus and plantar aponeurosis; insertion, middle phalanges of four lateral toes by tendons perforated by those of the flexor digitorum longus; action, flexes lateral four toes; nerve supply, medial plantar. SYN: musculus flexor digitorum brevis [TA], musculus flexor brevis digitorum, short flexor (muscle) of toes.