The Appendicular Skeleton: Structure and Key Features

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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 includes 126 bones and is essential for movement and manipulation of the environment.

Main Divisions: Pectoral (shoulder) girdle, pelvic (hip) girdle, upper limbs, and lower limbs.
Function: Provides support, facilitates movement, and protects organs associated with locomotion and reproduction.
Examples: Clavicle, scapula, humerus, radius, ulna, hip bones, femur, tibia, fibula.

The Pectoral (Shoulder) Girdle

Structure and Components

The pectoral girdle attaches the upper limbs to the trunk and consists of two bones on each side: the clavicle and the scapula.

Clavicle: Also known as the collarbone; connects the arm to the body and stabilizes shoulder movement.
Scapula: Also known as the shoulder blade; provides attachment points for muscles and articulates with the humerus at the glenoid cavity.

Key Anatomical Markings of the Pectoral Girdle

Important landmarks on the clavicle and scapula serve as attachment points for muscles and ligaments, and facilitate joint movement.

Important Markings	Description
Acromial (lateral) end	Flattened lateral end that articulates with the acromion of the scapula at the acromioclavicular (AC) joint.
Sternal (medial) end	Oval or triangular medial end that articulates with the sternum.
Conoid tubercle	Small, cone-shaped projection located on the lateral, inferior surface; serves to anchor ligaments.
Superior border	Short, sharp border located superiorly on the scapula.
Medial (vertebral) border	Thin, long border that runs roughly parallel to the vertebral column.
Lateral (axillary) border	Thick border that is closest to the armpit and ends superiorly at the glenoid cavity.
Glenoid cavity	A shallow socket that articulates with the head of the humerus to form the shoulder joint.
Spine	A ridge of bone on the posterior surface of the scapula that is easily felt through the skin.
Acromion	The lateral end of the spine of the scapula that articulates with the acromial end of the clavicle at the AC joint.
Coracoid process	Projects above the glenoid cavity as a hooklike process; helps attach the biceps brachii muscle.
Suprascapular notch	Small notch located medial to the coracoid process that allows for the passage of blood vessels and a nerve.
Subscapular fossa	A large shallow depression that forms the anterior surface of the scapula.
Supraspinous fossa	A depression located superior to the spine of the scapula.
Infraspinous fossa	A broad depression located inferior to the spine of the scapula.

Functional Significance

Joint Formation: The pectoral girdle forms the shoulder joint, allowing a wide range of motion for the upper limb.
Muscle Attachment: Numerous muscles attach to the clavicle and scapula, enabling movements such as abduction, rotation, and flexion of the arm.
Protection: The girdle helps protect underlying neurovascular structures.

Example: Shoulder Joint Movement

The glenoid cavity of the scapula articulates with the head of the humerus, forming the glenohumeral joint, which is a ball-and-socket joint allowing for extensive mobility.

Additional info: The appendicular skeleton also includes the pelvic girdle and the bones of the limbs, which are covered in other sections of the course. The pectoral girdle is crucial for upper limb mobility and stability.