The internal thoracic (mammary) nerve.
D001341:Autonomic Nervous System; D001940:Breast / Q000294:innervation; D006801:Humans; D010791:Phrenic Nerve / Q000196:embryology; D013900:Thoracic Nerves / Q000196:embryology*; D013950:Thymus Gland / Q000294:innervation