Bones of the Pectoral Girdle, Humerus, and Forearm

Bones of the Pectoral Girdle

Structure and Features of the Scapula

The scapula, or shoulder blade, is a flat, triangular bone that forms the posterior part of the pectoral girdle. It provides attachment points for several muscles and articulates with the humerus and clavicle.

• Acromion: The lateral extension of the scapular spine; articulates with the clavicle.

• Coracoid process: A hook-like projection on the anterior surface; serves as an attachment for muscles and ligaments.

• Glenoid cavity (fossa): A shallow depression that articulates with the head of the humerus to form the shoulder joint.

• Spine: A prominent ridge running across the posterior surface, dividing it into the supraspinous and infraspinous fossae.

• Supraspinous fossa: The area above the spine; origin of the supraspinatus muscle.

• Infraspinous fossa: The area below the spine; origin of the infraspinatus muscle.

• Medial (vertebral) border: Closest to the vertebral column.

• Lateral (axillary) border: Closest to the armpit.

• Superior border: The uppermost edge of the scapula.

Example: The glenoid cavity is the site of articulation with the humerus, forming the glenohumeral (shoulder) joint.

Bones of the Arm: The Humerus

Structure and Features of the Humerus

The humerus is the single long bone of the upper arm, extending from the shoulder to the elbow. It articulates proximally with the scapula and distally with the radius and ulna.

• Head: The rounded proximal end that fits into the glenoid cavity of the scapula.

• Anatomical neck: The slight constriction immediately distal to the head.

• Surgical neck: The region just below the tubercles; common site of fractures.

• Greater and lesser tubercles: Projections for muscle attachment near the head.

• Deltoid tuberosity: A roughened area on the lateral surface for attachment of the deltoid muscle.

• Medial and lateral epicondyles: Bony projections at the distal end for muscle attachment.

• Capitulum: A rounded eminence on the lateral distal end that articulates with the radius.

• Trochlea: A spool-shaped surface on the medial distal end that articulates with the ulna.

• Olecranon fossa: A large depression on the posterior distal end that receives the olecranon of the ulna during elbow extension.

• Coronoid fossa: A depression on the anterior distal end that receives the coronoid process of the ulna during elbow flexion.

Example: The deltoid tuberosity is the site where the deltoid muscle attaches, allowing for abduction of the arm.

Bones of the Forearm

Radius and Ulna: Structure and Articulation

The forearm consists of two parallel long bones: the radius (lateral, thumb side) and the ulna (medial, little finger side). These bones articulate with each other at the proximal and distal radioulnar joints and with the humerus at the elbow.

• Radius:

  • Head: Disc-shaped proximal end that articulates with the capitulum of the humerus and the radial notch of the ulna.

  • Radial tuberosity: A rough projection below the head for attachment of the biceps brachii muscle.

  • Styloid process: A pointed projection at the distal end, palpable at the wrist.

• Ulna:

  • Olecranon process: The prominent, curved projection at the proximal end; forms the point of the elbow.

  • Coronoid process: A projection below the olecranon; fits into the coronoid fossa of the humerus during elbow flexion.

  • Trochlear notch: The deep notch between the olecranon and coronoid processes; articulates with the trochlea of the humerus.

  • Ulnar tuberosity: A rough area below the coronoid process for muscle attachment.

  • Styloid process: A pointed projection at the distal end, palpable at the wrist.

• Interosseous membrane: A fibrous sheet connecting the radius and ulna along their lengths, providing additional surface area for muscle attachment.

Example: The head of the radius allows for rotation of the forearm, enabling pronation and supination movements.

Comparison Table: Key Features of the Radius and Ulna

Feature	Radius	Ulna
Location	Lateral (thumb side)	Medial (little finger side)
Proximal Articulation	Capitulum of humerus, radial notch of ulna	Trochlea of humerus, radial notch receives head of radius
Distal Feature	Styloid process (lateral wrist)	Styloid process (medial wrist)
Major Proximal Process	Head (disc-shaped)	Olecranon process
Function in Movement	Rotates for pronation/supination	Forms hinge joint at elbow

Additional info: The pectoral girdle, humerus, and forearm bones are essential for upper limb mobility and stability, providing attachment points for muscles and forming joints that allow a wide range of movements.