Musculus pectoralis major

The pectoralis major (from Latin pectus 'breast') is a thick, fan-shaped or triangular convergent muscle, situated at the chest of the human body.

It makes up the bulk of the chest muscles and lies under the breast.

Beneath the pectoralis major is the pectoralis minor, a thin, triangular muscle.

The pectoralis major's primary functions are flexion, adduction, and internal rotation of the humerus.

The pectoral major may colloquially be referred to as "pecs", "pectoral muscle" or "chest muscle" due to it being the largest and most superficial muscle in the chest area.