The Appendicular Skeleton: Pectoral Girdle and Upper Limb

The Appendicular Skeleton

Overview

The appendicular skeleton consists of the bones of the limbs and the girdles that attach them to the axial skeleton. It is essential for movement and manipulation of the environment.

• Pectoral girdle: Attaches the upper limbs to the trunk.

• Pelvic girdle: Attaches the lower limbs to the trunk.

• Upper and lower limbs differ in function but share the same basic structural plan.

The Pectoral Girdle

Structure and Function

The pectoral girdle is composed of two bones: the clavicle and the scapula. Together, they anchor the upper limbs to the axial skeleton and provide a wide range of motion for the arms.

• The pectoral girdles do not completely encircle the body.

• Medial end of each clavicle articulates with the manubrium of the sternum and the first rib.

• Lateral end of each clavicle articulates with the scapula at the acromioclavicular joint.

• The scapulae do not join each other or the axial skeleton directly.

Clavicles

Anatomy and Articulations

The clavicles, or collarbones, are slender, S-shaped bones that lie horizontally across the superior thorax. They serve as braces for the scapulae and arms, holding them laterally away from the thorax.

• Sternal (medial) end: Articulates with the manubrium of the sternum.

• Acromial (lateral) end: Articulates with the acromion of the scapula.

• Clavicles are palpable and often used as anatomical landmarks.

• They transmit mechanical force from the upper limb to the trunk.

Key Landmarks:

• Conoid tubercle (inferior surface, near lateral end)

• Trapezoid line (inferior surface, near lateral end)

Scapulae

Location and Borders

The scapulae, or shoulder blades, are thin, triangular bones located on the dorsal surface of the rib cage, between ribs 2 and 7. They provide attachment points for numerous muscles and articulate with the humerus and clavicle.

• Each scapula has three borders:

  • Superior border

  • Medial (vertebral) border

  • Lateral (axillary) border

• Each scapula has three angles:

  • Lateral angle (contains the glenoid cavity)

  • Superior angle

  • Inferior angle

Major Landmarks of the Scapula

• Acromion: Lateral projection that articulates with the clavicle.

• Coracoid process: Anterior projection for muscle attachment.

• Glenoid cavity (fossa): Shallow socket that articulates with the head of the humerus to form the shoulder joint.

• Spine: Prominent ridge on the posterior surface, ending in the acromion.

• Supraspinous fossa: Depression above the spine.

• Infraspinous fossa: Depression below the spine.

• Subscapular fossa: Broad anterior surface of the scapula.

• Suprascapular notch: Passage for nerves.

Functional Significance

• The arrangement of the pectoral girdle allows for a high degree of mobility at the shoulder joint.

• The shallow glenoid cavity permits a wide range of motion but provides less stability compared to the hip joint.

Example: The flexibility of the pectoral girdle enables actions such as throwing, lifting, and reaching overhead, which are essential for daily activities and athletic performance.