The Appendicular Skeleton: Structure and Features of the Upper Limb

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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. The upper limb includes the pectoral girdle, arm, forearm, and hand.

Pectoral girdle: Composed of the clavicle and scapula, connecting the upper limb to the trunk.
Arm: Contains the humerus, the single bone of the upper arm.
Forearm: Includes the radius and ulna.
Hand: Consists of carpals (wrist), metacarpals (palm), and phalanges (fingers).

Full skeleton with appendicular skeleton highlighted

Pectoral Girdle

Clavicle

The clavicle (collarbone) is a slender, S-shaped bone that acts as a strut between the sternum and scapula. It stabilizes the shoulder and allows for a wide range of arm movements.

Sternal end: Articulates with the manubrium of the sternum.
Acromial end: Articulates with the acromion of the scapula.

Clavicle highlighted in the pectoral girdle Clavicle sternal end highlighted Clavicle acromial end highlighted

Scapula

The scapula (shoulder blade) is a flat, triangular bone that provides attachment points for muscles and articulates with the humerus and clavicle.

Acromion: Lateral projection that articulates with the clavicle.
Coracoid process: Provides attachment for muscles of the arm and chest.
Glenoid cavity: Shallow socket that articulates with the head of the humerus.
Spine: Prominent ridge on the posterior surface.
Subscapular fossa: Broad depression on the anterior surface.

Scapula highlighted in the pectoral girdle Scapula spine highlighted Scapula acromion highlighted Scapula glenoid cavity highlighted Scapula coracoid process highlighted Scapula supraspinous fossa highlighted Scapula infraspinous fossa highlighted Scapula highlighted in skeleton Scapula subscapular fossa highlighted Scapula lateral border highlighted Scapula medial border highlighted Scapula scapular notch highlighted

Arm

Humerus

The humerus is the bone of the upper arm, articulating proximally with the scapula and distally with the radius and ulna. It is crucial for arm movement and muscle attachment.

Head: Articulates with the glenoid cavity of the scapula.
Anatomical neck: Slightly constricted region below the head.
Surgical neck: Common site of fractures.
Greater and lesser tubercles: Sites for muscle attachment.
Deltoid tuberosity: Attachment for the deltoid muscle.
Capitulum and trochlea: Distal articular surfaces for the radius and ulna.
Olecranon fossa: Accommodates the olecranon of the ulna during elbow extension.

Humerus anatomical features Humerus greater tubercle highlighted Humerus lesser tubercle highlighted Humerus intertubercular groove highlighted Humerus deltoid tuberosity highlighted Humerus surgical neck highlighted Humerus capitulum and trochlea highlighted Humerus capitulum highlighted Humerus trochlea highlighted Humerus olecranon fossa highlighted Humerus coronoid fossa highlighted Humerus highlighted in skeleton

Forearm

Radius and Ulna

The radius and ulna are the two bones of the forearm. The radius is lateral (thumb side), and the ulna is medial (little finger side). They articulate with each other at the proximal and distal radioulnar joints and with the humerus at the elbow.

Olecranon: Proximal end of the ulna, forms the elbow.
Coronoid process: Anterior projection of the ulna.
Trochlear notch: Articulates with the trochlea of the humerus.
Radial notch: Articulates with the head of the radius.
Styloid process: Distal projections of both radius and ulna.

Radius and ulna highlighted in skeleton Radius styloid process highlighted Ulna styloid process highlighted Ulna olecranon highlighted Ulna coronoid process highlighted Ulna trochlear notch highlighted Ulna radial notch highlighted

Hand

Carpals, Metacarpals, and Phalanges

The hand consists of three groups of bones: carpals (wrist), metacarpals (palm), and phalanges (fingers). The carpal bones are arranged in two rows and allow for flexibility and movement of the wrist.

Carpals: Eight bones forming the wrist.
Metacarpals: Five bones forming the palm.
Phalanges: Fourteen bones forming the fingers.

Hand bones and wrist x-ray Carpal bones highlighted Scaphoid bone highlighted Lunate bone highlighted Triquetrum bone highlighted Pisiform bone highlighted Trapezium bone highlighted Trapezoid bone highlighted Capitate bone highlighted Hamate bone highlighted

Summary Table: Major Bones and Features of the Upper Limb

Region	Bone	Key Features
Pectoral Girdle	Clavicle	Sternal end, Acromial end
Pectoral Girdle	Scapula	Acromion, Coracoid process, Glenoid cavity, Spine
Arm	Humerus	Head, Anatomical neck, Surgical neck, Greater/Lesser tubercle, Deltoid tuberosity, Capitulum, Trochlea, Olecranon fossa
Forearm	Radius	Head, Styloid process
Forearm	Ulna	Olecranon, Coronoid process, Trochlear notch, Styloid process
Hand	Carpals	Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate
Hand	Metacarpals	I-V (thumb to little finger)
Hand	Phalanges	Proximal, Middle, Distal (except thumb)

Example: The humerus articulates with the scapula at the glenoid cavity, forming the shoulder joint, and with the radius and ulna at the elbow joint, allowing for flexion and extension of the forearm.

Additional info: The appendicular skeleton is essential for locomotion and manipulation, and its structure reflects the functional demands placed on the upper limb.