Pectoralis Major – Functional Anatomy

Muscle

Dissection studies show that pectoralis major varies dramatically. There is commonly 2-5 laminates, sometimes 6 or 7, and sometimes the entire pectoralis is missing (Poland Syndrome). Also, the overlap of sections varies among studies. The variation illustrated here is common and I used it because, well, it was fun to illustrate and shows how differently laminates vary in their pull on the rib cage. It is commonly taught that it only has a clavicular and sternal section, which, is not the majority of cases. This version has costal and abdominal sections, which ties the humerus directly into the fascia of the abdominals and the pubic bone, and shows an interesting step in the evolutionary progression.

Clavicular section:

Origin: medial half of the clavicle

Insertion: lateral lip of bicipital groove, starting at the greater tubercle

Function: flexion, horizontal flexion and adduction of the glenohumeral joint

Sternal section:

Origin: manubrium and upper 3/4 of sternum

Insertion: lateral lip of bicipital groove, starting at the greater tubercle

Function: horizontal flexion and adduction of the glenohumeral joint, some internal rotation of the humerus, protraction of the scapula

Costal sections:

Often, there are 2 costal sections. The ventral portion lies on the superficial surface of the sternal section at the medial attachment. The dorsal section attaches to the costal cartilages inferior to the sternal section. These sections twist around the sternal and clavicular sections to attach beneath them on the bicipital groove. This twist, like the twist in latissimus dorsi, straightens when the arm is overhead.

Origin: costal cartilages of ribs. This may vary and attach as superior as rib 2 and attach as inferiorly as rib 8. The ventral section attaches to the lower sternum superficial to the sternal section.

Insertion: bicipital groove deep to the sternal and clavicular attachments.

Function: protraction and depression of the scapula, adduction, depression and horizontal flexion of the humerus

 

Abdominal section:

This section, which is often absent, ties the humerus into the fascia overlapping the abdominals, creating a line of muscle from the upper extremity, across the torso, to the pubic bone.

Origin: superficial fascia of the rectus abdominus and/or external oblique.

Insertion: bicipital groove deep to the sternal and clavicular attachments.

Function: protraction and depression of the scapula, adduction, depression and horizontal flexion of the humerus

  

Wikipedia entry for muscle

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Tony Preston has a practice in Atlanta, Georgia where he sees clients.

He has written and taught about anatomy, trigger points and cranial therapies since the mid-90s.

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