Source Institute • Pectoralis Major Course
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Upper Limb Pectoral Region Origin • Insertion • Action

Pectoralis Major Muscle (Right)

The pectoralis major is a broad, powerful muscle of the anterior chest wall. It spans from the clavicle, sternum, costal cartilages, and abdominal aponeurosis to the humerus. Because of its wide origin and strong insertion, it plays a major role in drawing the arm across the body, adducting the shoulder, and medially rotating the humerus.

Learning objectives

  • Identify the major origin sites of the pectoralis major.
  • Locate the insertion on the humerus.
  • Describe the muscle’s primary actions at the shoulder.
  • Name the nerves that innervate the pectoralis major.
  • Connect the anatomy to common movement patterns and palpation.

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Pectoralis major highlighted on the anterior chest
Section 1

Anatomy Overview

The pectoralis major is the large superficial chest muscle that forms much of the front wall of the axilla. It is commonly described in a clavicular portion and a sternocostal portion, with lower fibers also receiving attachment from the upper abdominal aponeurosis. The fibers converge laterally to a strong tendon on the proximal humerus.
Oblique translucent view showing the pectoralis major highlighted on the chest

Main visual

This oblique translucent view shows the pectoralis major spanning from the anterior chest wall to the proximal humerus. The broad origin and converging fiber direction help explain its powerful influence on shoulder movement.

Key facts

  • Region: pectoral region / anterior thorax
  • Joint influenced: glenohumeral joint
  • Primary movements: transverse adduction, adduction, medial rotation, and flexion (especially clavicular fibers)
  • Reverse action: can assist with elevating the thorax during forced inspiration when the upper limb is fixed

Origin

Hover to flip and review where the pectoralis major begins.

Origin review

Clavicular fibers: anterior aspect of the medial half of the clavicle.

Sternocostal fibers: anterior sternum and costal cartilages of ribs 1–6, with lower fibers blending with the abdominal aponeurosis.

Insertion

Hover to flip and review where the pectoralis major attaches.

Insertion review

The tendon inserts on the lateral lip of the intertubercular sulcus of the humerus, also described as the crest of the greater tubercle or lateral lip of the bicipital groove.

Action

Hover to flip and review the major movements produced by the muscle.

Action review

Main actions include shoulder transverse adduction, adduction, and medial rotation. The clavicular fibers also assist with shoulder flexion.

Tip: Hover your mouse over each card to flip it. On touch devices, tap the card to focus it.

Section 2

Origins of the Pectoralis Major

The pectoralis major arises from multiple sites. The clavicular head comes from the anterior surface of the medial half of the clavicle. The sternocostal head arises from the anterior sternum and adjacent costal cartilages, and inferior fibers blend with the aponeurosis of the external oblique / anterior rectus sheath.
Clavicular origin of pectoralis major highlighted in magenta on the clavicle

Clavicular origin

The clavicular part begins from the anterior aspect of the medial half of the clavicle. These upper fibers help with shoulder flexion and draw the arm across the body.

Sternocostal origin of pectoralis major highlighted in magenta on the sternum

Sternocostal origin

The sternocostal fibers arise from the anterior manubrium and body of the sternum, and are also associated with the costal cartilages of ribs 1 through 6. Lower fibers blend with the abdominal aponeurosis.

Section 3

Insertion

The fibers of the pectoralis major converge laterally into a strong tendon that inserts on the lateral lip of the intertubercular sulcus of the humerus, also described as the crest of the greater tubercle or the lateral lip of the bicipital groove.
Insertion of pectoralis major highlighted in magenta on the proximal humerus

Insertion site

The magenta highlight marks the insertion area on the proximal humerus. This lateral attachment gives the muscle strong leverage for moving the humerus toward the chest.

Why the insertion matters

  • The tendon crosses the front of the shoulder, allowing it to pull the humerus into adduction and medial rotation.
  • Because the insertion is on the humerus, the muscle can power pushing, hugging, and reaching-across-body movements.
  • Its twisting tendon arrangement contributes to the broad range of force directions produced by the upper and lower fibers.
Section 4

Actions

The pectoralis major is best known for drawing the arm across the front of the body. Its major actions are shoulder transverse adduction (horizontal adduction), adduction, and medial rotation. The clavicular head also assists with shoulder flexion, while the sternocostal fibers can assist with extension of the flexed arm back toward anatomical position.

Shoulder transverse adduction

Brings the arm across the front of the body, as in a hugging motion or pressing movement. This is one of the most recognizable actions of the pectoralis major.

Shoulder adduction

Pulls the arm toward the trunk from an abducted position. The broad lower fibers are especially helpful in powerful adduction.

Medial rotation

Rotates the humerus inward. This action works with other internal rotators such as the latissimus dorsi, teres major, and subscapularis.

Shoulder flexion

The clavicular fibers help raise the arm forward, especially from an extended or neutral position.

Action clip 1

Example of shoulder flexion with pectoralis major participation, especially by the clavicular fibers.

Action clip 2

Example of shoulder depression, lowering the shoulder girdle downward.

Action clip 3

Example of shoulder adduction, drawing the upper limb back toward the side of the body.

Anterior view of the pectoralis major highlighted on the chest

Anterior anatomy view

This anterior view shows the full size and fan-shaped arrangement of the pectoralis major across the chest. It helps students visualize the broad origin and the narrowing attachment toward the humerus.

Oblique translucent view of the pectoralis major highlighted on the chest

Oblique anatomy view

This oblique translucent view shows the pectoralis major traveling from the chest wall to the humerus. The fiber direction helps explain its role in adduction, medial rotation, and cross-body movement.

Section 5

Innervation

The pectoralis major is innervated by the lateral pectoral nerve and the medial pectoral nerve. The lateral pectoral nerve generally carries fibers from C5–C7, and the medial pectoral nerve generally carries fibers from C8–T1. Together, they supply the muscle and support its forceful upper-limb actions.
Isolated innervation path for pectoralis major

Isolate innervation path

This image isolates the relevant nerve pathway and shows the relationship between the pectoral nerves and the pectoralis major.

Highlighted innervation path for pectoralis major

Highlight innervation path

In this view, the highlighted pathway makes it easier to trace the course of the nerves as they approach the muscle.

Clinical reminder

When assessing anterior shoulder and chest function, keep in mind that the pectoralis major often works with the anterior deltoid, latissimus dorsi, teres major, and serratus anterior depending on the movement being performed. Tightness or tenderness may affect posture, shoulder range of motion, and patterns such as rounded shoulders.

Section 6

Knowledge Check

Answer the following questions to check your understanding of the pectoralis major muscle.

1. The clavicular fibers of the pectoralis major originate from:

2. The insertion of the pectoralis major is on the:

3. Which is a major action of the pectoralis major?

4. The pectoralis major is innervated by the:

5. The sternocostal fibers arise in part from the:

6. The clavicular portion especially assists with:

7. Medial rotation means the humerus rotates:

8. The pectoralis major forms much of the:

Pectoralis Major Muscle Course • Source Institute • Origin, insertion, innervation, and action review