Skeletal Anatomy: Skull, Vertebrae, Pectoral Girdle, and Upper Limb Bones

Overview of Skull Structure

Basic Structure of the Skull: Anterolateral View

The human skull is a complex structure composed of cranial and facial bones. These bones protect the brain and form the framework of the face.

• Cranial Bones: These bones encase and protect the brain. Major cranial bones include the frontal bone, parietal bone, temporal bone, occipital bone, sphenoid bone, and ethmoid bone.

• Facial Bones: These bones form the structure of the face and include the maxilla, zygomatic bone, nasal bone, mandible, lacrimal bone, palatine bone, inferior nasal concha, and vomer.

• Inferior Nasal Concha: A separate bone that forms part of the lateral walls of the nasal cavity.

Example: The frontal bone forms the forehead and the upper part of the eye sockets.

Structure of the Vertebrae

Thoracic Vertebrae

The thoracic vertebrae are part of the vertebral column and are located in the mid-back region. They articulate with the ribs and have unique features distinguishing them from cervical and lumbar vertebrae.

• Body: The thick, disc-shaped anterior portion that bears weight.

• Transverse Process: Lateral projections for muscle and ligament attachment; in thoracic vertebrae, they also articulate with ribs.

• Spinous Process: Posterior projection for muscle and ligament attachment.

• Lamina: Part of the vertebral arch between the transverse and spinous processes.

• Inferior and Superior Costal Facets: Articulation points for the ribs.

• Superior and Inferior Articular Facets: Articulate with adjacent vertebrae.

Example: The thoracic vertebrae (T1-T12) are distinguished by the presence of costal facets for rib articulation.

The Sacrum and Coccyx

The sacrum and coccyx are located at the base of the vertebral column. The sacrum is a triangular bone formed by the fusion of five sacral vertebrae, while the coccyx (tailbone) is formed by the fusion of three to five small vertebrae.

• Sacrum: Provides strength and stability to the pelvis.

• Coccyx: Serves as an attachment site for ligaments and muscles of the pelvic floor.

• Median Sacral Crest: The fused spinous processes of the sacral vertebrae.

• Auricular Surface: Articulates with the ilium of the hip bone.

• Transverse Lines: Indicate the sites of vertebral fusion.

• Sacral Promontory: The anterior projecting edge of the first sacral vertebra.

Example: The sacrum forms the posterior wall of the pelvic cavity.

The Pectoral Girdle

Structure 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 muscles and articulates with the humerus and clavicle.

• Medial Border: The edge closest to the vertebral column.

• Lateral Border: The edge closest to the arm.

• Superior Angle: The uppermost point of the scapula.

• Inferior Angle: The lowermost point of the scapula.

• Glenoid Cavity: A shallow socket that articulates with the head of the humerus.

• Coracoid Process: A hook-like projection for muscle attachment.

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

• Supraspinous and Infraspinous Fossae: Depressions above and below the scapular spine for muscle attachment.

Example: The glenoid cavity of the scapula forms the socket of the shoulder joint.

The Humerus

Structure of the Humerus

The humerus is the 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.

• Greater and Lesser Tubercles: Projections for muscle attachment.

• Shaft: The long, cylindrical midsection.

• Medial and Lateral Epicondyles: Projections at the distal end for muscle attachment.

• Capitulum and Trochlea: Articulate with the radius and ulna, respectively.

Example: The olecranon fossa on the posterior distal humerus receives the olecranon of the ulna during elbow extension.

Bones of the Forearm: The Radius and Ulna

Structure of the Radius and Ulna

The radius and ulna are the two long bones of the forearm. They run parallel to each other and articulate with the humerus at the elbow and with the carpal bones at the wrist.

• Radius: Located on the lateral (thumb) side of the forearm. The head of the radius articulates with the capitulum of the humerus and the radial notch of the ulna.

• Ulna: Located on the medial (pinky) side of the forearm. The olecranon process forms the point of the elbow and articulates with the trochlea of the humerus.

• Interosseous Membrane: A fibrous sheet connecting the radius and ulna along their lengths.

Example: During pronation and supination, the radius rotates around the ulna, allowing the hand to turn.

Summary Table: Key Bones and Features

Region	Main Bones	Key Features
Skull	Frontal, Parietal, Temporal, Occipital, Sphenoid, Ethmoid, Maxilla, Mandible, Zygomatic, Nasal, Inferior Nasal Concha, Vomer	Protects brain, forms face, houses sensory organs
Vertebral Column	Cervical, Thoracic, Lumbar Vertebrae, Sacrum, Coccyx	Supports body, protects spinal cord, allows movement
Pectoral Girdle	Scapula, Clavicle	Attaches upper limb to trunk, allows shoulder movement
Upper Limb	Humerus, Radius, Ulna	Movement and support of the arm and hand