Axial vs Appendicular
Skeleton: Major Landmarks
Master the two divisions of the human skeleton, learn to identify key bones and landmarks, and understand how they work together to support, protect, and move the body.
Anatomy & Physiology
What Is the Skeletal System?
The adult human skeleton is composed of 206 bones organized into two major divisions. Together, they provide the structural framework for the body, protect vital organs, anchor muscles, and store minerals like calcium and phosphorus.
Two Divisions: Axial & Appendicular
Axial Skeleton
80 bones forming the central axis: skull, vertebral column, rib cage, and hyoid bone. Primary role: protection of the brain, spinal cord, and thoracic organs.
Appendicular Skeleton
126 bones of the upper and lower limbs plus the pectoral and pelvic girdles. Primary role: movement and manipulation of the environment.
Full Skeleton Color-Coded Map
The Axial Skeleton: 80 Bones
Skull (22)
8 cranial bones + 14 facial bones that protect the brain and form the face.
Vertebral Column (26)
7 cervical, 12 thoracic, 5 lumbar, 1 sacrum (5 fused), 1 coccyx (4 fused).
Thoracic Cage (25)
12 pairs of ribs (24 total) + 1 sternum. Protects heart and lungs.
Associated Bones (7)
6 auditory ossicles (in the middle ear) and the 1 hyoid bone in the neck.
The Appendicular Skeleton: 126 Bones
Pectoral Girdle (4)
2 clavicles + 2 scapulae. Connects upper limbs to the axial skeleton.
Upper Limbs (60)
Humerus, radius, ulna, 8 carpals, 5 metacarpals, 14 phalanges per arm
Pelvic Girdle (2)
2 os coxae (hip bones), each formed by fused ilium, ischium, and pubis
Lower Limbs (60)
Femur, patella, tibia, fibula, 7 tarsals, 5 metatarsals, 14 phalanges per leg
The Division Principle
The fundamental rule for classifying any bone into the axial or appendicular skeleton:
The girdles (pectoral and pelvic) are the connecting bridges: they belong to the appendicular skeleton because their primary function is to attach limbs to the trunk.
Vertebral Column Regions
Pectoral vs Pelvic Girdle
| Pectoral Girdle | Pelvic Girdle | |
|---|---|---|
| Bones | Clavicle + Scapula | Os Coxa (ilium, ischium, pubis) |
| Attachment | Loosely via sternum | Firmly fused to sacrum |
| Mobility | High: wide range of motion | Low: stability for weight |
| Function | Flexibility for reaching | Support and weight transfer |
| Division | Appendicular | Appendicular |
How to Classify Any Bone
1
Name the bone. Identify it precisely (e.g., "scapula" not just "shoulder bone").
2
Ask: Is it on the midline axis? Skull, vertebrae, ribs, sternum, and hyoid = axial.
3
Ask: Is it part of a limb? Arms, hands, legs, feet = appendicular.
4
Ask: Is it a girdle bone? Clavicle, scapula, os coxa = appendicular (they bridge limb to axis).
5
Verify the total. Axial bones should sum to 80, appendicular to 126 = 206 total.
Example: Skull Landmarks
Example: Upper Limb Bones
Example: Lower Limb Bones
The Thoracic Cage: Ribs & Sternum
True Ribs (1-7)
Attach directly to the sternum via their own costal cartilage. Also called vertebrosternal ribs.
False Ribs (8-10)
Connect to the sternum indirectly through the costal cartilage of rib 7. Called vertebrochondral ribs.
Floating Ribs (11-12)
No anterior attachment to the sternum at all. Called vertebral ribs. Protect kidneys posteriorly.
Why Are Girdles Appendicular?
A common confusion: the pectoral and pelvic girdles sit close to the axial skeleton, yet they are classified as appendicular. Here is the reasoning:
1
Function over location. Girdles exist to connect limbs to the trunk: their primary role is limb attachment, not axial support.
2
They develop with the limbs. Embryologically, girdle bones arise from the same mesenchyme as limb bones.
3
They move with the limbs. The scapula glides across the back during arm movement; the pelvis tilts during walking.
Common Mistakes
✕ Girdles are axial
The clavicle, scapula, and os coxae are appendicular: they bridge limbs to the axis, not support the axis itself.
✕ Sacrum is appendicular
The sacrum is part of the vertebral column and therefore axial, even though it articulates with the pelvic girdle.
✕ Forgetting the hyoid
The hyoid is often overlooked. It is the 80th axial bone, located in the neck, and is the only bone not articulating with another bone.
✕ Confusing rib types
True ribs (1-7) attach directly to sternum. False ribs (8-10) attach indirectly. Floating ribs (11-12) have no anterior attachment.
Summary Comparison
| Feature | Axial | Appendicular |
|---|---|---|
| Bone Count | 80 | 126 |
| Primary Role | Protection & support | Movement & manipulation |
| Major Regions | Skull, vertebral column, thoracic cage, hyoid | Pectoral girdle, upper limbs, pelvic girdle, lower limbs |
| Position | Central longitudinal axis | Lateral, extending from axis |
| Key Landmark | Foramen magnum | Acetabulum |
| Clinical Note | Vertebral fractures, skull trauma | Fractures of femur, clavicle (most fractured bone) |
Question 1 of 5
Which of the following bones is part of the axial skeleton?
The sternum is part of the thoracic cage, which belongs to the axial skeleton (80 bones). The scapula and clavicle are appendicular (pectoral girdle), and the femur is an appendicular lower limb bone.
Question 2 of 5
How many bones make up the appendicular skeleton in an adult human?
The appendicular skeleton contains 126 bones: 4 in the pectoral girdle, 60 in the upper limbs, 2 in the pelvic girdle, and 60 in the lower limbs. The axial skeleton has 80, and the total skeleton has 206.
Question 3 of 5
The sacrum is classified as part of which skeletal division?
The sacrum is part of the vertebral column and therefore belongs to the axial skeleton, even though it articulates with the appendicular pelvic girdle (os coxae). Remember: the sacrum supports the axis, not the limbs.
Question 4 of 5
Which bone is unique because it does not articulate with any other bone?
The hyoid bone is the only bone in the body that does not articulate with any other bone. It is a U-shaped axial bone in the neck that is suspended by muscles and ligaments. It anchors the tongue and aids in swallowing.
Question 5 of 5
The foramen magnum is a major landmark found on which bone?
The foramen magnum ("great hole") is located at the base of the occipital bone. It is the opening through which the spinal cord exits the cranium and connects to the brainstem. This is one of the most important axial skeleton landmarks.