Appendicular Skeleton and Articulations: Bones, Markings, and Major Ligaments

Appendicular Skeleton

Pectoral Girdle

The pectoral girdle connects the upper limbs to the axial skeleton and provides attachment points for muscles that move the shoulders and arms.

• Scapula (shoulder blade) (2): Flat, triangular bones located on the posterior thorax.

  • Spine: Prominent ridge on the posterior surface.

  • Acromion: Lateral extension of the spine; articulates with the clavicle.

  • Coracoid process: Anterior projection for muscle attachment.

  • Supraspinous fossa: Depression above the spine.

  • Infraspinous fossa: Depression below the spine.

  • Glenoid cavity: Shallow socket for the humerus head.

  • Subscapular fossa: Broad anterior surface.

  • Lateral border: Edge closest to the arm.

  • Medial border: Edge closest to the vertebral column.

  • Superior angle: Uppermost point.

  • Inferior angle: Lowermost point.

• Clavicle (collarbone) (2): S-shaped bones that connect the scapula to the sternum.

Upper Extremity

• Humerus (2): The upper arm bone, articulates with the scapula at the shoulder and the radius and ulna at the elbow.

  • Head: Proximal, rounded end that fits into the glenoid cavity.

  • Neck: Narrow region just below the head.

  • Surgical neck: Common fracture site, below the tubercles.

  • Greater tubercle: Lateral projection for muscle attachment.

  • Lesser tubercle: Anterior projection for muscle attachment.

  • Deltoid tuberosity: Rough area for deltoid muscle attachment.

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

  • Trochlea: Spool-shaped structure that articulates with the ulna.

  • Capitulum: Rounded structure that articulates with the radius.

  • Coronoid fossa: Receives the coronoid process of the ulna during flexion.

  • Olecranon fossa: Receives the olecranon of the ulna during extension.

• Ulna (2): Medial bone of the forearm (pinky side).

  • Olecranon: Point of the elbow.

  • Coronoid process: Anterior projection at the proximal end.

  • Trochlear notch: Articulates with the trochlea of the humerus.

  • Styloid process: Distal projection.

• Radius (2): Lateral bone of the forearm (thumb side).

  • Head: Disc-shaped proximal end.

  • Neck: Narrow region below the head.

  • Styloid process: Distal projection.

• Carpals (16): Eight small bones per wrist, forming the wrist joint.

• Metacarpals (10): Five bones per hand, forming the palm.

• Phalanges (28): Bones of the fingers; three per finger, two in the thumb (pollex).

Pelvic Girdle

The pelvic girdle supports the weight of the upper body and protects pelvic organs.

• Coxal Bone (os coxae) (2): Each hip bone is formed by the fusion of three bones: ilium, ischium, and pubis.

  • Acetabulum: Deep socket for the femur head.

  • Obturator foramen: Large opening for nerves and blood vessels.

  • Ilium: Superior portion.

    • Iliac crest: Superior border.

    • Iliac fossa: Large, smooth depression.

    • Anterior superior/inferior iliac spine: Projections for muscle attachment.

    • Posterior superior/inferior iliac spine: Posterior projections.

    • Greater sciatic notch: Passage for sciatic nerve.

  • Ischium: Inferior, posterior portion.

    • Ischial spine: Pointed projection.

    • Lesser sciatic notch: Below the ischial spine.

    • Ischial tuberosity: Supports body weight when sitting.

  • Pubis: Anterior portion.

    • Pubic symphysis: Joint between pubic bones.

    • Pubic tubercle: Small projection near the symphysis.

Lower Extremity

• Femur (2): Thigh bone, the longest and strongest bone in the body.

  • Head: Articulates with the acetabulum.

  • Neck: Connects head to shaft.

  • Greater and lesser trochanters: Projections for muscle attachment.

  • Gluteal tuberosity: Posterior ridge for gluteal muscle attachment.

  • Linea aspera: Long ridge on posterior shaft.

  • Medial/lateral condyles: Articulate with tibia.

  • Medial/lateral epicondyles: Above the condyles.

  • Intercondylar fossa: Depression between condyles.

• Patella (2): Kneecap, a sesamoid bone in the quadriceps tendon.

• Tibia (2): Medial, weight-bearing bone of the lower leg.

  • Medial/lateral condyles: Proximal expansions for femur articulation.

  • Tibial tuberosity: Anterior bump for patellar ligament attachment.

  • Medial malleolus: Distal projection at the ankle.

• Fibula (2): Lateral, slender bone of the lower leg.

  • Lateral malleolus: Distal projection at the ankle.

• Tarsals (14): Seven bones per ankle, including the talus (ankle bone) and calcaneus (heel bone).

• Metatarsals (10): Five bones per foot, forming the arch.

• Phalanges (28): Bones of the toes; three per toe, two in the big toe (hallux).

Articulations (Joints)

Knee Joint

The knee joint is a complex synovial joint that allows flexion, extension, and slight rotation of the leg. It is stabilized by several ligaments.

• Patellar ligament: Connects the patella to the tibial tuberosity.

• Popliteal ligaments (2): Reinforce the posterior aspect of the knee.

• Anterior cruciate ligament (ACL): Prevents anterior displacement of the tibia.

• Posterior cruciate ligament (PCL): Prevents posterior displacement of the tibia.

• Tibial collateral ligament (medial): Stabilizes the medial side of the knee.

• Fibular collateral ligament (lateral): Stabilizes the lateral side of the knee.

Example: The ACL is commonly injured in sports that involve sudden stops and changes in direction.

Shoulder Joint

The shoulder joint (glenohumeral joint) is a ball-and-socket joint with a wide range of motion, stabilized by several ligaments.

• Acromioclavicular ligament: Connects the acromion of the scapula to the clavicle.

• Coraco-acromial ligament: Connects the coracoid process to the acromion, forming an arch over the humeral head.

• Coracoclavicular ligament: Connects the coracoid process to the clavicle, providing vertical stability.

Example: Separation of the acromioclavicular joint is a common shoulder injury.

Summary Table: Major Bones and Markings of the Appendicular Skeleton

Region	Bone	Key Markings/Features
Pectoral Girdle	Scapula	Spine, acromion, coracoid process, glenoid cavity, fossae, borders, angles
Pectoral Girdle	Clavicle	Sternal end, acromial end
Upper Limb	Humerus	Head, neck, tubercles, epicondyles, trochlea, capitulum, fossae
Upper Limb	Ulna	Olecranon, coronoid process, trochlear notch, styloid process
Upper Limb	Radius	Head, neck, styloid process
Hand	Carpals, Metacarpals, Phalanges	Numbered I-V, proximal/distal phalanges, pollex
Pelvic Girdle	Coxal Bone	Ilium, ischium, pubis, acetabulum, obturator foramen
Lower Limb	Femur	Head, neck, trochanters, condyles, epicondyles, linea aspera
Lower Limb	Patella	Base, apex
Lower Limb	Tibia	Condyles, tuberosity, medial malleolus
Lower Limb	Fibula	Lateral malleolus
Foot	Tarsals, Metatarsals, Phalanges	Talus, calcaneus, hallux

Additional info:

• The appendicular skeleton consists of 126 bones, including those of the limbs and girdles.

• Joints (articulations) are classified by structure (fibrous, cartilaginous, synovial) and function (synarthrosis, amphiarthrosis, diarthrosis).

• Ligaments are dense regular connective tissue structures that connect bones and stabilize joints.