Appendicular Skeleton: Structure and Terminology

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 plays a crucial role in movement and manipulation of the environment.

• Pectoral girdle: Attaches the upper limbs to the trunk; consists of the clavicle and scapula.

• Pelvic girdle: Attaches the lower limbs to the trunk; consists of the hip bones (os coxae).

• Upper limbs: Includes the humerus, radius, ulna, carpals, metacarpals, and phalanges.

• Lower limbs: Includes the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.

Example: The pectoral girdle allows for a wide range of motion in the shoulder, enabling activities such as throwing or lifting.

Major Components of the Appendicular Skeleton

Region	Bones	Number
Pectoral girdle	Clavicle, Scapula	4
Upper limbs	Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges	60
Pelvic girdle	Hip bones (os coxae)	2
Lower limbs	Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges	60

Upper Limb Bones

Pectoral Girdle

The pectoral girdle consists of the clavicle and scapula, which provide attachment points for muscles and support the upper limbs.

• Clavicle: S-shaped bone with two ends: the acromial end (lateral, articulates with scapula) and the sternal end (medial, articulates with sternum).

• Scapula: Triangular bone with key features such as the acromion (forms the highest point of the shoulder), spine (ridge on the posterior surface), and glenoid fossa (cavity) (articulates with the head of the humerus).

Humerus

The humerus is the single bone of the upper arm, connecting the shoulder to the elbow.

• Head: Articulates with the glenoid cavity of the scapula.

• Greater and Lesser Tubercles: Sites for muscle attachment.

• Shaft: The long, central portion of the bone.

• Deltoid Tuberosity: Roughened area for deltoid muscle attachment.

• Distal Features: Trochlea (articulates with ulna), Capitulum (articulates with radius), Olecranon fossa (receives olecranon of ulna), Medial and Lateral Epicondyles (muscle attachment sites).

Forearm Bones: Radius and Ulna

The forearm consists of two parallel bones: the radius (lateral) and the ulna (medial).

• Radius: Features include the radial head (articulates with capitulum of humerus), styloid process (distal projection), and radial notch (articulates with ulna).

• Ulna: Features include the olecranon (forms the elbow), ulnar head (distal end), and styloid process (distal projection).

Bones of the Hand

The hand consists of the carpal bones (wrist), metacarpals (palm), and phalanges (fingers).

• Carpals: Eight small bones forming the wrist.

• Metacarpals: Five bones forming the palm.

• Phalanges: Fourteen bones forming the fingers (proximal, middle, and distal phalanges).

• Pollex: The thumb, which has only two phalanges (proximal and distal).

Lower Limb Bones

Pelvic Girdle

The pelvic girdle consists of two hip bones (os coxae), which articulate with the sacrum and support the lower limbs.

• Acetabulum: Deep socket that receives the head of the femur.

• Pubic symphysis: Cartilaginous joint uniting the left and right pubic bones.

Femur

The femur is the longest and strongest bone in the body, forming the thigh.

• Femoral head: Articulates with the acetabulum of the pelvis.

• Neck: Connects the head to the shaft.

• Greater and Lesser Trochanters: Muscle attachment sites.

• Shaft: Long, central portion.

• Linea aspera: Ridge on the posterior shaft for muscle attachment.

• Distal Features: Medial and Lateral Condyles (articulate with tibia), Medial and Lateral Epicondyles (muscle attachment), Patella (kneecap, protects knee joint).

Leg Bones: Tibia and Fibula

The leg contains two bones: the tibia (medial, weight-bearing) and the fibula (lateral, slender).

• Tibia: Features include medial and lateral condyles (articulate with femur), tibial tuberosity (attachment for patellar ligament), and medial malleolus (forms medial ankle bulge).

• Fibula: Features include head (proximal end), lateral malleolus (forms lateral ankle bulge).

Bones of the Foot

The foot consists of tarsal bones (ankle), metatarsals (sole), and phalanges (toes).

• Tarsals: Seven bones including the calcaneus (heel) and talus (articulates with tibia and fibula).

• Metatarsals: Five bones forming the sole.

• Phalanges: Fourteen bones forming the toes (proximal, middle, and distal phalanges).

• Arches of the foot: Medial longitudinal, lateral longitudinal, and transverse arches provide support and flexibility.

Key Terminology

Important Anatomical Terms

Understanding the terminology associated with bones is essential for identifying features and discussing anatomical relationships.

• Epicondyle: A projection above a condyle, often for muscle attachment.

• Fossa: A shallow depression or hollow in a bone.

• Process: A projection or outgrowth from a bone.

• Tuberosity: A large, rounded projection for muscle attachment.

• Trochanter: Large, blunt projection found only on the femur.

• Condyle: Rounded articular projection.

• Head: Rounded, proximal end of a bone, often fitting into a fossa.

• Shaft: The elongated, central part of a long bone.

Summary Table: Major Bones and Features

Bone	Key Features
Clavicle	Acromial end, Sternal end
Scapula	Acromion, Spine, Glenoid fossa
Humerus	Head, Greater/Lesser tubercles, Deltoid tuberosity, Trochlea, Capitulum, Olecranon fossa, Epicondyles
Radius	Head, Styloid process, Radial notch
Ulna	Olecranon, Styloid process, Ulnar head
Femur	Head, Neck, Greater/Lesser trochanters, Linea aspera, Condyles, Epicondyles
Tibia	Medial/Lateral condyles, Tibial tuberosity, Medial malleolus
Fibula	Head, Lateral malleolus
Hand	Carpals, Metacarpals, Phalanges, Pollex
Foot	Tarsals, Metatarsals, Phalanges, Calcaneus, Talus

Additional info:

• Images and diagrams referenced in the notes are essential for visual identification of bone features and should be reviewed alongside these notes for comprehensive understanding.

• Students should be able to identify each bone and its key features on both diagrams and physical models.