The medial pectoral nerve (medial anterior thoracic) arises from the medial cord of the brachial plexus and through it from the eighth cervical and first thoracic.
It passes behind the first part of the axillary artery, curves forward between the axillary artery and vein, and unites in front of the artery with a filament from the lateral nerve.
It then enters the deep surface of the Pectoralis minor, where it divides into a number of branches, which supply the muscle.
Two or three branches pierce the muscle and end in the Pectoralis major. A mnemonic to differentiate the medial pectoral nerve, which pierces both pectorals, from the lateral pectoral nerve, which pierces only Pectoralis major, is "Lateral Less, Medial More".
Brachial plexus with courses of spinal nerves shown
This article incorporates text from a public domain edition of Gray's Anatomy.