Appendicular Skeleton: Structure and Function

Appendicular Skeleton

Overview

The appendicular skeleton consists of the bones of the limbs and their supporting girdles. It is responsible for facilitating movement and connecting the limbs to the axial skeleton.

• Pectoral (shoulder) girdle: Attaches the upper limbs to the body trunk.

• Pelvic (hip) girdle: Attaches the lower limbs to the body trunk.

Pectoral Girdle (Shoulder Girdle)

Structure and Function

The pectoral girdle consists of two bones on each side of the body:

• Clavicle (anteriorly)

• Scapula (posteriorly)

These bones attach the upper limbs to the axial skeleton and provide attachment sites for muscles that move the upper limbs. The pectoral girdle offers a high degree of mobility due to:

• The scapulae are not directly attached to the axial skeleton, allowing for greater movement.

• The socket of the shoulder joint (glenoid cavity) is shallow, which does not restrict movement.

Articulating Bones of the Pectoral Girdle

• Acromioclavicular joint: The joint where the clavicle meets the acromion of the scapula.

• Clavicle: The collarbone, running horizontally between the sternum and scapula.

• Scapula: The shoulder blade, a flat, triangular bone located on the posterior side of the rib cage.

Clavicles

Structure and Articulations

The clavicles, commonly known as collarbones, are slender, S-shaped bones that serve as struts to support the shoulder.

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

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

• Clavicles provide attachment points for muscles and act as braces to hold the scapulae and arms out laterally.

Key Features of the Clavicle

• Sternal (medial) end: Rounded and articulates with the sternum.

• Acromial (lateral) end: Flattened and articulates with the scapula.

• The clavicle is easily palpable and is often fractured due to its subcutaneous position.

Example: Right Clavicle

• The right clavicle, when viewed from above (superior view), shows the sternal end medially and the acromial end laterally.

Additional info: The clavicle acts as a shock absorber and transmits mechanical force from the upper limb to the axial skeleton. Its curvature increases resilience, and its subcutaneous location makes it vulnerable to fractures, especially from falls on an outstretched hand.