The second muscle layer in the sole of the foot is associated with the tendons of the flexor digitorum longus muscle, which pass through this layer, and consists of the quadratus plantae and four lumbrical muscles (Fig. 6.120 and Table 6.12).
The quadratus plantae muscle is a flat quadrangular muscle with two heads of origin (Fig. 6.120):
One of the heads originates from the medial surface of the calcaneus inferior to the sustentaculum tali.