The Skeleton

The Thoracic Cage

The thoracic cage is a vital bony structure of the chest, composed of the thoracic vertebrae, ribs, sternum, and costal cartilages. It serves to protect essential organs, support the shoulder girdles and upper limbs, and provide attachment sites for muscles.

• Components: Thoracic vertebrae (posterior), ribs (lateral), sternum and costal cartilages (anterior)

• Functions: Protection of heart and lungs, support for upper limbs, muscle attachment

Sternum

The sternum, or breastbone, consists of three fused bones: the manubrium, body, and xiphoid process. It features important anatomical landmarks and is not fully ossified until about age 40.

• Manubrium: Superior portion, articulates with clavicular notches and ribs 1 and 2

• Body: Midportion, articulates with costal cartilages of ribs 2–7

• Xiphoid process: Inferior end, site of muscle attachment

• Landmarks: Jugular notch, sternal angle, xiphisternal joint

Clinical Note: Xiphoid Process

In some individuals, the xiphoid process projects posteriorly. Trauma to this area can cause severe injury to underlying organs such as the liver or heart. During CPR, hands must be placed on the midsternum to avoid breaking the xiphoid process.

Ribs

The ribs form the sides of the thoracic cage, with 12 pairs attaching posteriorly to the thoracic vertebrae. They are classified as true, false, or floating ribs based on their attachment to the sternum.

• True (vertebrosternal) ribs: Pairs 1–7, attach directly to sternum via individual costal cartilages

• False (vertebrochondral) ribs: Pairs 8–10, attach indirectly by joining costal cartilage of rib above

• Floating (vertebral) ribs: Pairs 11–12, no attachment to sternum

Structure of a Typical Rib

Each rib has several distinct parts that facilitate articulation and muscle attachment.

• Shaft: Flat bone forming most of the rib

• Head: Posterior end, articulates with vertebrae

• Neck: Constricted portion beyond head

• Tubercle: Knoblike structure, articulates with transverse costal facet

The Appendicular Skeleton

Pectoral Girdle

The pectoral girdle consists of the clavicle and scapula, attaching the upper limbs to the body trunk. Its structure allows for a high degree of mobility and provides muscle attachment sites.

• Clavicle: S-shaped bone, articulates medially with sternum and laterally with scapula

• Scapula: Thin, triangular bone on dorsal surface of rib cage

• Mobility: Scapulae are not attached to axial skeleton; shoulder joint socket is shallow

Clavicle

• Sternal end: Articulates with sternum

• Acromial end: Articulates with scapula

• Function: Anchors muscles, acts as brace for scapulae and arms

Scapula

• Borders: Superior, medial (vertebral), lateral (axillary)

• Angles: Superior, lateral, inferior

• Features: Spine, acromion, coracoid process, suprascapular notch, fossae (subscapular, supraspinous, infraspinous)

The Upper Limb

Arm

The arm contains the humerus, the largest and longest bone of the upper limb. It articulates with the scapula, radius, and ulna.

• Head: Fits into glenoid cavity of scapula

• Anatomical neck: Slight constriction below head

• Greater and lesser tubercles: Sites of rotator cuff muscle attachment

• Surgical neck: Most frequently fractured part

• Radial groove: Carries radial nerve

• Trochlea and capitulum: Distal condyles for articulation

• Epicondyles: Muscle attachment points

• Fossae: Coronoid, olecranon, radial

Forearm

The forearm consists of two parallel bones: the ulna (medial) and radius (lateral). They articulate with the humerus and each other, connected by the interosseous membrane.

• Ulna: Forms major portion of elbow joint; features olecranon and coronoid processes, trochlear notch, radial notch, ulnar head, and styloid process

• Radius: Articulates with capitulum of humerus and radial notch of ulna; features head, radial tuberosity, ulnar notch, and styloid process

Clinical Note: Colles’ Fracture

A break in the distal end of the radius, common when a person falls and attempts to break the fall with outstretched hands.

Hand

The hand is composed of the carpus (wrist), metacarpus (palm), and phalanges (fingers).

• Carpus: Eight bones in two rows (proximal: scaphoid, lunate, triquetrum, pisiform; distal: trapezium, trapezoid, capitate, hamate)

• Metacarpus: Five metacarpal bones (I–V) from thumb to little finger

• Phalanges: Fingers I–V; thumb (pollex) has two bones, other fingers have three (distal, middle, proximal)

Clinical Note: Carpal Tunnel Syndrome

The median nerve and tendons pass through the carpal tunnel, formed by ligaments. Overuse and inflammation can compress the median nerve, causing tingling and numbness.

Table: Bones of the Appendicular Skeleton (Pectoral Girdle and Upper Limb)

Additional info: The notes above expand on brief points with academic context, definitions, and clinical relevance to ensure completeness and clarity for exam preparation.