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Muscles and Fascia of the Chest

Q: Which muscles are classified as deep (intrinsic) chest muscles?

Deep or intrinsic chest muscles include six groups. External intercostal muscles (mm. intercostales externi)Internal intercostal muscles (mm. intercostales interni)Innermost intercostal muscles (mm. intercostales intimi)Subcostal muscles (mm. subcostales)Transversus thoracis muscle (m. transversus thoracis)Levatores costarum — long and short (mm. levatores costarum longi et breves)

Q: Where does the pectoralis major muscle originate and insert?

The pectoralis major muscle (m. pectoralis major) originates from the clavicle, sternum, ribs, and the rectus sheath, and inserts into the humerus. Origin: Medial half of the clavicle (pars clavicularis), anterior surface of the sternum and cartilages of ribs II–VII (pars sternocostalis), and the anterior wall of the rectus abdominis sheath (pars abdominalis).Insertion: Crest of the greater tubercle of the humerus. The tendon forms a double U-shaped fold, with the upper bundles lying distal to the lower ones.

Q: Where does the pectoralis minor muscle originate and insert?

The pectoralis minor muscle (m. pectoralis minor) is a superficial chest muscle. It originates on the anterior surface of the thoracic cage and inserts into the scapula. Origin: Anterior ends and costal cartilages of ribs II to V.Insertion: Coracoid process of the scapula.

Q: Where is the transversus thoracis muscle located and what functions does it perform?

The transversus thoracis muscle (m. transversus thoracis) originates from the inner surface of the lower sternum, xiphoid process, and cartilages of ribs III–VI. It inserts into the inner surfaces of the cartilages of ribs II–VI. Functions: Acts as a weak expiratory muscle, pulling the costal cartilages posteriorly and inferiorly; tenses the anterior thoracic wall.

Musculi thoracis

For medical students2 min readUpdated 2026-10-10

The anterolateral chest wall is a complex anatomical structure comprising various topographic regions and muscle layers. The muscles of this area play a key role both in movements of the shoulder girdle and in the biomechanics of respiratory rib excursions.

TopographyThe anterolateral thoracic wall is clearly divided into exactly four anatomical regions.

Fiber courseThe fibers of the subcostal muscles are characterized by skipping over one or two ribs.

RespirationThe lower muscle bundles of the serratus anterior act as powerful inspiratory stabilizers.

Topographic Regions of the Thoracic Wall

For precise localization of pathological processes and surgical approaches, the anterolateral chest wall is typically divided into four main regions:

Sternal region (regio sternalis). Located most medially, running directly along the sternum. Topographically, it corresponds precisely to the anterior median line of the body.
Pectoral region (regio pectoralis). An extensive zone projected over the site of the pectoralis major muscle. The mammary gland is also located here.
Axillary region (regio axillaris). Topographically corresponds to the lower section of the shoulder girdle. Includes the axilla. This zone has clear muscular boundaries formed by the pectoralis major, latissimus dorsi, and serratus anterior muscles.
Inframammary region (regio inframammaria, or regio hypochondriaca anterior). The lowest segment of the anterolateral wall. It extends downward to the costal arches, where it transitions directly into the hypochondriac regions.

Serratus Anterior Muscle

The m. serratus anterior is a critical element for the fixation and movement of the scapula. Its maximum development and largest muscle mass are noted in the area projected over the inferior angle of the scapula.

Points of origin: The muscle originates via 8–9 distinct muscular slips from the outer surface of the upper ribs, from rib I to IX.
Insertion point: The fibers run posteriorly and attach to the anterior surface of the scapula — along its medial border and at the inferior angle.
Biomechanics (function): The main task of the muscle is to pull the scapula anteriorly and laterally. This results in outward and upward rotation of the scapula, which is a prerequisite for elevating the upper extremity above the horizontal plane. Additionally, the muscle firmly presses and fixes the scapula against the rib cage. Notably, the lower bundles act as a powerful stabilizer and accessory muscle during inspiration.
Innervation: Provided by the long thoracic nerve (n. thoracicus longus), originating from segments C5–C7.
Blood supply: Supplied by branches of the thoracodorsal (a. thoracodorsalis), lateral thoracic (a. thoracica lateralis), and intercostal arteries (aa. intercostales).

Subcostal Muscles

The subcostal muscles (mm. subcostales) belong to the intrinsic deep musculature of the thoracic cage and lie on its internal surface.

Localization: They are located predominantly in the posterolateral regions of the thoracic wall, attaching to the inner surface of the lower ribs. A distinct feature of their bundles is that they do not attach to the adjacent rib, but rather skip 1–2 ribs downward.
Biomechanics (function): These are muscles of expiration. By contracting, they actively pull the ribs downward and medially, decreasing the volume of the thoracic cavity.
Innervation: Intercostal nerves (nn. intercostales), corresponding to segments Th7–Th12.
Blood supply: Nourishment is provided by the posterior intercostal arteries (aa. intercostales posteriores).

Frequently asked questions

Which muscles are classified as superficial chest muscles?

Superficial chest muscles include four muscles that embryologically originate from the upper limb.

Pectoralis major muscle (m. pectoralis major)
Pectoralis minor muscle (m. pectoralis minor)
Subclavius muscle (m. subclavius)
Serratus anterior muscle (m. serratus anterior)

Which muscles are classified as deep (intrinsic) chest muscles?

Deep or intrinsic chest muscles include six groups.

External intercostal muscles (mm. intercostales externi)
Internal intercostal muscles (mm. intercostales interni)
Innermost intercostal muscles (mm. intercostales intimi)
Subcostal muscles (mm. subcostales)
Transversus thoracis muscle (m. transversus thoracis)
Levatores costarum — long and short (mm. levatores costarum longi et breves)

Where does the pectoralis major muscle originate and insert?

The pectoralis major muscle (m. pectoralis major) originates from the clavicle, sternum, ribs, and the rectus sheath, and inserts into the humerus.

Origin: Medial half of the clavicle (pars clavicularis), anterior surface of the sternum and cartilages of ribs II–VII (pars sternocostalis), and the anterior wall of the rectus abdominis sheath (pars abdominalis).
Insertion: Crest of the greater tubercle of the humerus. The tendon forms a double U-shaped fold, with the upper bundles lying distal to the lower ones.

What fasciae are identified in the chest region?

The chest region features the superficial pectoral fascia and the parietal thoracic fascia.

Pectoral fascia (fascia pectoralis) — covers the anterior chest wall. It is subdivided into a superficial lamina (lamina superficialis), deep lamina (lamina profunda), and clavipectoral fascia (fascia clavipectoralis).
Thoracic fascia (parietal) (fascia thoracica) — a thin membrane covering the outer surface of the intercostal muscles and ribs across the entire thoracic wall.

Where does the pectoralis minor muscle originate and insert?

The pectoralis minor muscle (m. pectoralis minor) is a superficial chest muscle. It originates on the anterior surface of the thoracic cage and inserts into the scapula.

Origin: Anterior ends and costal cartilages of ribs II to V.
Insertion: Coracoid process of the scapula.

Where is the transversus thoracis muscle located and what functions does it perform?

The transversus thoracis muscle (m. transversus thoracis) originates from the inner surface of the lower sternum, xiphoid process, and cartilages of ribs III–VI. It inserts into the inner surfaces of the cartilages of ribs II–VI.

Functions: Acts as a weak expiratory muscle, pulling the costal cartilages posteriorly and inferiorly; tenses the anterior thoracic wall.

How many anatomical regions is the anterolateral thoracic wall divided into?

Topographic anatomy distinguishes exactly 4 regions: sternal, pectoral, axillary, and inframammary.

Which muscle enables a person to raise their arm above the shoulder (horizontal) level?

This movement is driven by the serratus anterior muscle. By contracting, it rotates the scapula with its inferior angle outward and upward, carrying the glenoid fossa and the entire arm with it.

Where exactly are the subcostal muscles located and what is their unique feature?

They are located on the inner surface of the posterolateral parts of the lower ribs. Their main feature is that their fiber bundles do not span to the neighboring rib, but rather skip one or two ribs downward.

Go deeper

Anatomy and Boundaries of the Axillary Fossa
Intrinsic Chest Fasciae: Superficial, Pectoral, and Endothoracic
Topography and Structure of the Mammary Gland
Other Superficial and Deep Chest Muscles (Pectoralis Major/Minor, Intercostals)
Course and Branching of the Long Thoracic Nerve