The human skeleton is divided into two main parts: the axial skeleton, which forms the central core of your body, and the appendicular skeleton, which includes your limbs and the structures that attach them to that core. Together, these two divisions account for all 206 bones in the adult body, with 80 in the axial skeleton and 126 in the appendicular skeleton.
The Axial Skeleton: Your Body’s Central Framework
The axial skeleton runs along the midline of your body, forming the vertical axis everything else connects to. Its 80 bones are organized into five groups: the skull, the tiny bones of the middle ear, the hyoid bone in the neck, the vertebral column (spine), and the thoracic cage (ribcage).
Your skull houses and protects the brain, while also forming the structure of your face. It contains both cranial bones (the dome around the brain) and facial bones (the framework for your eyes, nose, jaw, and cheeks). Deep inside each ear sit three tiny bones called ossicles, the smallest bones in the body, which transmit sound vibrations. Below the skull, a single U-shaped bone called the hyoid sits in your neck and supports the tongue and throat muscles. It’s unusual because it doesn’t directly articulate with any other bone.
The vertebral column is made up of 33 vertebrae in total, divided into four regions: 7 cervical vertebrae in the neck, 12 thoracic vertebrae in the mid-back, 5 lumbar vertebrae in the lower back, 5 sacral vertebrae, and 4 coccygeal vertebrae at the base. By adulthood, the five sacral vertebrae fuse into a single bone (the sacrum), and the four coccygeal vertebrae fuse into the tailbone (coccyx), which is why the column is often counted as 26 individual bones in adults.
The thoracic cage wraps around the chest and includes the sternum (breastbone) and 12 pairs of ribs. This bony enclosure protects the heart, lungs, and other vital organs while also playing an active role in breathing. The ribs flex slightly with each breath, expanding and contracting the chest cavity.
The Appendicular Skeleton: Limbs and Girdles
The appendicular skeleton accounts for 126 bones and includes everything that isn’t along the central axis: both arms, both legs, and the two girdles that connect them to the trunk. “Appendicular” comes from the Latin word for “to hang upon,” which makes sense since the limbs essentially hang from the axial core.
The pectoral girdle (shoulder girdle) connects each upper limb to the axial skeleton. It consists of two bones on each side: the clavicle (collarbone) and the scapula (shoulder blade). From there, each upper limb contains the humerus in the upper arm, the radius and ulna in the forearm, eight small carpal bones in the wrist, five metacarpals in the palm, and 14 phalanges in the fingers. That’s 30 bones per arm, plus the two girdle bones on each side.
The pelvic girdle connects the lower limbs to the spine. Each side of the pelvis is formed by a large hip bone that is itself a fusion of three bones (the ilium, ischium, and pubis), which merge during adolescence. Below the pelvis, each lower limb includes the femur (thighbone), the patella (kneecap), the tibia and fibula in the lower leg, seven tarsal bones in the ankle, five metatarsals in the midfoot, and 14 phalanges in the toes. Your hands and feet alone contain more than half of all the bones in the appendicular skeleton.
How the Two Divisions Connect
The axial and appendicular skeletons aren’t independent structures floating side by side. They physically connect at specific joints. The upper limb’s connection point is the sternoclavicular joint, where the inner end of the collarbone meets the top of the sternum. This is the only bony joint between the entire upper limb and the axial skeleton. The scapula, by contrast, is held in place almost entirely by muscles, which is part of what gives the shoulder its wide range of motion.
The lower limb connects to the axial skeleton at the sacroiliac joint, where each hip bone meets the sacrum at the base of the spine. This joint is much more rigid than the sternoclavicular joint, which reflects the lower limb’s primary role in weight-bearing and stability rather than wide-ranging mobility.
Different Functions, Different Priorities
The two divisions have distinct jobs. The axial skeleton is built primarily for protection and support. The skull shields the brain, the vertebral column encases the spinal cord, and the ribcage guards the heart and lungs. It also provides the central anchor point for muscles and the stable base that posture depends on.
The appendicular skeleton is built for movement. The bones in your arms and legs act as levers, and the joints between them allow the pulling, pushing, walking, and gripping that get you through daily life. The trade-off is that appendicular bones are generally more exposed and more vulnerable to fractures than the well-protected axial bones.
This functional split goes all the way back to embryonic development. The axial skeleton originates from a tissue layer called the paraxial mesoderm, while the appendicular skeleton develops from a different layer called the lateral plate mesoderm. These are distinct cell populations that differentiate early in fetal development, which is why certain genetic conditions can affect one division of the skeleton without impacting the other.
Why the 206 Number Varies
You’ll see “206 bones” cited as the standard adult count, but the real number can vary slightly from person to person. Some people have extra small bones called sesamoid bones that form within tendons, or sutural bones that develop along the seams of the skull. The number of coccygeal vertebrae can range from three to five. Children have significantly more bones than adults because many bones that are separate at birth gradually fuse together over the first two decades of life. The sacrum alone starts as five separate pieces. The standard count of 80 axial and 126 appendicular bones represents the typical adult skeleton after all that fusion is complete.