The Appendicular Skeleton: Structure and Features

The Appendicular Skeleton

Overview of the Appendicular Skeleton

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: Composed of the scapula (shoulder blade) and clavicle (collarbone).

• Upper Limbs: Includes the humerus, radius, ulna, carpals, metacarpals, and phalanges.

• Pelvic Girdle: Formed by fused bones: ilium, ischium, and pubis.

• Lower Limbs: Consists of the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.

Function: The appendicular skeleton enables locomotion and manipulation of objects.

Pectoral Girdle

Structure and Function

The pectoral girdle attaches the upper limbs to the trunk and provides both mobility and stability for the arms.

• Components: Scapula and clavicle.

• Function: Allows a wide range of motion for the upper extremities while maintaining stability.

Scapula (Shoulder Blade)

General Structure

The scapula is a flat, triangular bone with three borders and three angles, serving as a major attachment site for muscles and ligaments of the shoulder.

• Superior Border: Contains the suprascapular notch.

• Medial (Vertebral) Border: Closest to the vertebral column.

• Lateral (Axillary) Border: Near the armpit; contains the glenoid cavity for articulation with the humerus.

• Angles: Superior, inferior, and lateral angles.

Scapula Features

• Subscapular Fossa: Large concave depression on the anterior surface; origin for the subscapularis muscle.

• Supraspinous Fossa: Shallow depression above the spine on the posterior surface; origin for the supraspinatus muscle.

• Infraspinous Fossa: Large depression below the spine on the posterior surface; origin for the infraspinatus muscle.

• Spine of Scapula: Prominent ridge on the posterior surface; ends laterally as the acromion.

• Acromion: Lateral projection; articulates with the clavicle.

• Coracoid Process: Anterior projection; attachment for muscles and ligaments.

• Glenoid Cavity (Fossa): Shallow socket on the lateral aspect; articulates with the head of the humerus to form the shoulder joint.

• Supraglenoid and Infraglenoid Tubercles: Sites for muscle attachment (biceps and triceps, respectively).

Clinical Note: The orientation of the glenoid cavity and the spine helps distinguish right from left scapula.

Clavicle

Structure and Articulations

The clavicle, or collarbone, is an S-shaped bone that acts as a strut between the scapula and the sternum, stabilizing the shoulder.

• Sternal (Medial) End: Articulates with the manubrium of the sternum at the sternoclavicular joint.

• Acromial (Lateral) End: Articulates with the acromion of the scapula at the acromioclavicular joint.

• Inferior Surface Features: Includes the conoid tubercle and trapezoid line for ligament attachment.

• Function: Acts as a brace to hold the scapula and arm laterally away from the thorax.

Clinical Note: The clavicle is the most commonly fractured bone in the body due to its subcutaneous position and the forces transmitted through the upper limb.

Summary Table: Key Features of the Pectoral Girdle

Bone	Main Features	Articulations	Function
Scapula	Spine, acromion, coracoid process, glenoid cavity, fossae	Humerus (glenohumeral joint), clavicle (acromioclavicular joint)	Muscle attachment, shoulder movement
Clavicle	Sternal end, acromial end, conoid tubercle, trapezoid line	Sternum (sternoclavicular joint), scapula (acromioclavicular joint)	Stabilizes shoulder, transmits forces

Additional info: The appendicular skeleton also includes the bones of the upper and lower limbs, as well as the pelvic girdle, which will be covered in further detail in subsequent sections or lectures.