The lumbrical muscles act through the extensor hoods to resist excessive extension of the metatarsophalangeal joints and flexion of the interphalangeal joints when the heel leaves the ground during walking.
The first lumbrical is innervated by the medial plantar nerve, while the other three are innervated by the lateral plantar nerve.
There are three muscles in the third layer in the sole of the foot (Fig. 6.122 and Table 6.13):