The muscles of the anterior aspect of the trunk

Name of muscle

Position

Attachments

Action/s

Key facts

Pectoralis major

(pek-to-ra-lis may-jor)

Thick, fan-shaped muscle covering the anterior surface of the upper chest

Attaches to the clavicle and the sternum at one end and to the humerus at the other end

Adducts arm, medially (inwardly) rotates arm

Tightness in this muscle can cause restrictions of the chest and postural disortions (rounded shoulders)

Pectoralis minor (pek-to-ra-lis my-nor)

Thin muscle that lies beneath the pectoralis major

Fibres attach laterally and upwards from the ribs at one end to the scapula at the other end

Draws the shoulder downwards and forwards

Used during forced expiration, as in coughing

Accessory respiratory muscle

Serratus anterior (ser-at-tus an-tee-ri-or)

Broad, curved muscle located on the side of the chest/rib cage below the axilla

Attaches to the outer surface of the upper eighth or ninth rib at one end and to the inner surface of the scapula, along the medial edge nearest the spine

Pulls the scapula downwards and forwards

Has a serrated appearance which comes from attaching onto separate ribs

External obliques

(eks-turn-al o-bleek)

Laterally at the sides of the waist

Fibres slant downwards from the lower ribs to the pelvic girdle and the linea alba (tendon running from the bottom of the sternum to the pubic symphysis)

Flexes, rotates and sidebends the trunk It compresses the contents of the abdomen

Often referred to as the pocket muscles as their fibres run in the direction in which you put your hands in your pocket

Internal obliques (in-turn-al o-bleek)

Broad, thin sheet of muscle located beneath the external obliques

Fibres run up and forward from the pelvic girdle to the lower ribs

Flexes, rotates and sidebends the trunk

Compresses the contents of the abdomen

Fibres of the internal obliques are deeper and run at right angles to the external obliques

Rectus abdominis

(rek-tus ab-dom-i-nis)

Long, strap-like muscle extending medially along the length of the abdomen

Attaches to the pubic bones at one end and the ribs and the sternum at the other

Flexes the vertebral column, flexes the trunk (as in a sit-up), compresses the abdominal cavity

Has three fibrous bands that give the muscle a segmented appearance and divides it into the so-called 'six pack'

Transversus abdominus

(trans-ver-sus ab-dom-i-nis)

Large, deep muscle with fibres extending across anterior of abdominal cavity

Attaches to the inner surfaces of the ribs (last six) and iliac crest at one end and extends down to the pubis via the linea alba (a long tendon that extends from the bottom of the sternum to the pubic symphysis)

Compression of the abdominal contents and supports the organs of the abdominal cavity

Often called the corset muscle because it wraps around the abdomen like a corset

The muscles of respiration 135

Deltoid

Pectoralis major

External oblique

Deltoid

Pectoralis major

External oblique

Transverse Abdominis

Pectoralis minor

Internal intercostal

Serratus anterior

Rectus abdominis

Internal oblique

Transversus abdominis

Pectoralis minor

Internal intercostal

Serratus anterior

Rectus abdominis

Internal oblique

Transversus abdominis

Fig 4.12 The muscles of the anterior of the trunk

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