Quadratus Plantae
Foot
Corrects the diagonal pull of flexor digitorum longus — without it, your toes would curl sideways.
Function
Adjusts pull of FDL tendons so toes flex straight (not obliquely)
Origin
Medial and lateral calcaneus
Insertion
Tendons of flexor digitorum longus
Innervation
Lateral plantar nerve (S1-S3)