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The main trunks of the medial and lateral plantar nerves and arteries lie deep to the first layer of muscles of the sole of the foot. To reflect the muscles of the first layer, first cut through the flexor digitorum brevis muscle close to its attachment to the calcaneus and reflect it distally. Next, cut the proximal portion of abductor hallucis muscle and reflect it distally.

Links and References:
Grant's: 5.105
Netter (1ed.): 501 (2ed.): 497
Rohen/Yokochi: 470