Learning Objectives
By the end of this topic, students should be able to:
- Identify the muscles of the pectoral region.
- Describe the attachments, actions, and innervation of each muscle.
- Explain the role of these muscles in movements of the upper limb and scapula.
- Recognize the clinical significance of injury to the long thoracic nerve.
Overview
The pectoral region is located on the anterior chest wall. It contains four muscles that act on the upper limb and scapula:
- Pectoralis major
- Pectoralis minor
- Serratus anterior
- Subclavius
These muscles form part of the anterior axillary wall and play a key role in upper limb movement and stability. This section reviews their attachments, actions, and innervation.
Pectoralis Major
The pectoralis major is the most superficial muscle of the pectoral region. It is large and fan-shaped, and consists of two heads: a clavicular head and a sternocostal head.
Attachments
- Clavicular head: originates from the anterior surface of the medial clavicle.
- Sternocostal head: originates from the anterior surface of the sternum, the superior six costal cartilages, and the aponeurosis of the external oblique muscle.
- Both heads insert into the intertubercular sulcus of the humerus.
Function
- Adducts and medially rotates the upper limb.
- Draws the scapula anteroinferiorly.
- The clavicular head also flexes the upper limb.
Innervation
- Medial and lateral pectoral nerves
Pectoralis Minor
The pectoralis minor lies deep to the pectoralis major and forms part of the anterior wall of the axilla.
Attachments
- Originates from ribs 3–5.
- Inserts into the coracoid process of the scapula.
Function
- Stabilises the scapula by drawing it anteroinferiorly against the thoracic wall.
Innervation
- Medial pectoral nerve
Serratus Anterior
The serratus anterior is located on the lateral chest wall and forms the medial border of the axilla.
Attachments
- Originates from the lateral surfaces of ribs 1–8.
- Inserts on the costal surface of the medial border of the scapula.
Function
- Protracts the scapula and holds it against the ribcage.
- Rotates the scapula to allow elevation of the arm above 90°.
Innervation
- Long thoracic nerve
Subclavius
The subclavius is a small muscle lying beneath the clavicle. It protects underlying neurovascular structures.
Attachments
- Originates from the junction of the 1st rib and its costal cartilage.
- Inserts onto the inferior surface of the middle third of the clavicle.
Function
- Anchors and depresses the clavicle.
Innervation
- Nerve to the subclavius
Clinical Relevance: Winging of the Scapula
The serratus anterior holds the scapula against the thoracic wall. Injury to the long thoracic nerve causes paralysis of this muscle.
As a result, the scapula protrudes posteriorly, producing a characteristic “winged” appearance. This condition commonly occurs due to traction injuries, where the upper limb is violently stretched.
