The medial pectoral nerve (medial anterior thoracic) arises from the medial cord

Medial cord

The Medial cord is a division of the brachial plexus.The medial cord gives rise to the following nerves:*The median pectoral nerve, C8 and T1, to the pectoralis muscle*The medial brachial cutaneous nerve, T1...

 of the brachial plexus

Brachial plexus

The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...

 and through it from the eighth cervical

Cervical vertebrae

In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...

 and first thoracic

Thoracic vertebrae

In human anatomy, twelve thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. They are intermediate in size between those of the cervical and lumbar regions; they increase in size as one proceeds down the spine, the upper...

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It passes behind the first part of the axillary artery

Axillary artery

In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla and the upper limb...

, curves forward between the axillary artery and vein, and unites in front of the artery with a filament from the lateral nerve

Lateral pectoral nerve

The lateral pectoral nerve arises from the lateral cord of the brachial plexus, and through it from the fifth, sixth, and seventh cervical nerves....

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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.