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Anatomy Chapter 10B: Anterior Trunk Muscles


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External Intercostals
11 pairs lie between ribs, form part of abdominal wall

O: inferior border of superior rib

I: superior border of inferior rib

A: pull ribs toward one another to elevate rib cage
Internal Intercostals
11 pairs lie between ribs, at right angles to the fibres of the external instercostals.

O: superior border of inferior rib

I: inferior border of superior rib

A: draw ribs together and depress rib cage
Broad muscle that forms floor of thoracic cavity.

O: inferior, internal surface of rib cage and sternum, costal cartilages of last 6 ribs and lumbar vertebrae

I: central tendon

A; prime mover of inspiration
Rectus Abdominus
Medial superficial muscle pair extending from the pubis to the rib cage. Segmented by 3 tendinous intersections.

O: pubic crest and symphysis

I: xiphoid process and costal cartilages of ribs 5-7

A: flex and rotate lumbar region of vertebral column
External Oblique
Largest and most superficial of the lateral anterior trunk muscles.

O: attached to outer surfaces of lower eight ribs by fleshy strips.

I: insert to linea alba via broad aponeurosis, some into pubic crest and iliac crest

A: aid rectus abdominis muscles (synergist) in flexing vertebral column and in compressing abdominal wall and increasing intra-abdominal pressure.
Internal Oblique
Muscle fans along sides, above hips, deep to the external obliques.

O: lumbar fascia, iliac crest, and inguinal ligament

I: linea alba, pubic crest, last three or four ribs, and costal margin

A: Aids rectus abdominis and external oblique (synergist) in flexing vertebral column and in compressing the abdominal wall and increasing intra-abdominal pressure.
Transversus Abdominus
Deepest muscle of the abdominal wall.

O: inguinal ligament, lumbar fascia, cartilages of last six ribs, iliac crest

I: linea alba, pubic crest

A: compresses abdominal contents.
Pectoralis Minor
Flat, thin muscle directly beneath and obscured by pectoralis major

O: anterior surfaces of ribs 3-5

I: coracoid process of scapula

A: draws scapula forward and downward
Serratus Anterior
Lies deep to scapula, beneath and inferior to pectoral muscles on lateral rib cage.

O: attached by a series of muscle slips to ribs 1-8

I: entire anterior surface of vertebral border of scapula

A: prime mover to protract and hold scapula against chest wall
Thick, multipennate muscle forming rounded shoulder muscle mass

O: embraces insertion of the trapezius, lateral third of clavicle, acromion and spine of scapula

I: deltoid tuberosity of humerus

A: prime mover of arm abduction
Pectoralis Major
Large, fan-shaped muscle covering the upper portion of the chest.

O: sternal end of clavicle, sternum, cartilage of ribs 1-6, and aponeurosis of external oblique muscle

I: fibres converge to insert by a short tendon into intertubercular groove of humerus

A: Prime mover of arm (upper arm) flexion

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