The adult human skeleton contains 206 bones, divided into two main groups: the axial skeleton (the central core) and the appendicular skeleton (the limbs and the structures that attach them). Newborns start with 275 to 300 separate bones, but many of these fuse together during childhood through a process called ossification, reaching the final count by early adulthood.
Understanding which bones belong where, and what they actually do, gives you a practical map of how your body supports itself, protects vital organs, and allows movement.
The Two Divisions of the Skeleton
The axial skeleton runs down the center of your body. It includes the skull, the vertebral column (spine), and the rib cage. Its primary job is protection: shielding the brain, spinal cord, heart, and lungs.
The appendicular skeleton accounts for 126 bones. It includes the shoulder girdle, the arms and hands, the pelvic girdle, and the legs and feet. These bones are built for movement and weight-bearing rather than organ protection, though the pelvis does double duty by cradling organs in the lower abdomen.
Skull: Cranial and Facial Bones
Your skull is made up of 22 bones total: eight cranial bones that form a protective shell around the brain, and 14 facial bones that shape your face and house the sensory organs for smell, sight, and taste.
The frontal bone forms your forehead and the roof of your eye sockets. It also contains the frontal sinuses, those hollow spaces behind your brow that can fill with pressure during a cold. Below the cranial bones, the major facial bones include the mandible (jawbone), which is the only movable bone in your entire skull, essential for chewing and speaking. The two maxilla bones form the upper jaw, the roof of your mouth, the floor of your nasal cavity, and part of the floor of your eye sockets. The zygomatic bones create your cheekbones, and the small nasal bones form the bridge of your nose.
Tucked inside the skull, in the middle ear, sit the three smallest bones in your body: the malleus, incus, and stapes. These tiny bones form a chain that transmits sound vibrations from the eardrum to the inner ear, where they are converted into nerve signals your brain interprets as sound.
The Spine: 33 Vertebrae in Five Regions
Your spine is a column of 33 vertebrae stacked on top of each other, separated by cushioning discs. It is organized into five distinct regions, each with a different job.
- Cervical spine (neck): Seven vertebrae (C1 through C7) support the weight of your head and allow it to rotate and tilt.
- Thoracic spine (middle back): Twelve vertebrae (T1 through T12) anchor the back of your rib cage and limit excessive bending to protect the chest organs.
- Lumbar spine (lower back): Five vertebrae (L1 through L5) carry most of your body’s weight and serve as attachment points for the powerful muscles of your back.
- Sacrum: Five vertebrae that fuse together during fetal development into a single triangular bone. The sacrum forms the back wall of the pelvis.
- Coccyx (tailbone): Four fused vertebrae at the very bottom of the spine. Despite its small size, the coccyx serves as an anchor point for muscles and ligaments in the pelvic floor.
Of these 33 vertebrae, only the top 24 remain as individual, movable bones in adulthood. The sacrum and coccyx, having fused, each count as a single bone.
The Rib Cage
The rib cage is built from 24 ribs (12 pairs) plus the sternum, or breastbone, a long flat bone running down the center of your chest. Together they form a bony enclosure around the heart and lungs while remaining flexible enough to expand with every breath. The upper seven pairs of ribs attach directly to the sternum via cartilage. The next three pairs connect indirectly, and the bottom two pairs, called “floating ribs,” attach only to the spine at the back and have no connection to the sternum at all.
Shoulder Girdle and Upper Limbs
Each shoulder is anchored by two bones: the clavicle (collarbone) and the scapula (shoulder blade). The clavicle acts as a strut, holding your arm away from the trunk, while the scapula provides a socket for the upper arm bone and attachment points for muscles that move the shoulder.
The upper arm contains a single bone, the humerus, which runs from your shoulder to your elbow. The forearm has two: the radius on the thumb side and the ulna on the pinky side. These two bones rotate around each other, which is what lets you turn your palm up or down.
The hand and wrist are surprisingly complex. Eight small carpal bones form the wrist, five metacarpals span the palm, and 14 phalanges make up the fingers (two in each thumb, three in each finger). That gives each hand 27 bones, making the hands one of the most bone-dense regions in the body.
Pelvic Girdle
The pelvis consists of two large hip bones (sometimes called innominate bones) that connect to the sacrum at the back and meet each other at the front. Each hip bone is itself a fusion of three bones that merge during adolescence: the ilium (the broad upper flare you feel at your waist), the ischium (the “sit bones” you rest on in a chair), and the pubis at the front.
The pelvis differs noticeably between sexes. In people with female anatomy, the pelvic inlet is nearly circular and the overall canal is wider to accommodate childbirth. The angle where the two pubic bones meet at the front is roughly 90 degrees. In people with male anatomy, that angle narrows to about 60 degrees, the sacrum is longer and more curved, and the upper flare of the hip bones is more extensive, making the pelvis overall larger but with a narrower internal opening.
Lower Limbs
The femur (thighbone) is the longest and strongest bone in the body. In most adults it measures around 18 inches, and it can support roughly 30 times your body weight. It runs from the hip socket to the knee, where it meets the two bones of the lower leg.
The tibia (shinbone) is the larger of the two lower leg bones and bears the vast majority of your weight. The fibula, thinner and running alongside the tibia on the outer side, mainly serves as an anchor for muscles and helps stabilize the ankle joint. The patella (kneecap) sits in front of the knee within the tendon of the thigh muscle, protecting the joint and improving the leverage of the muscles that straighten your leg.
The foot mirrors the complexity of the hand. Seven tarsal bones form the ankle and heel (the largest being the calcaneus, or heel bone), five metatarsals span the midfoot, and 14 phalanges make up the toes. Each foot has 26 bones, making the two feet alone account for about a quarter of all the bones in your body.
What Bones Are Made Of
Bones are not solid all the way through. They contain two types of tissue. The outer layer is compact bone, a dense, hard material that gives bones their strength and smooth white appearance. It is organized into tightly packed cylindrical units, each with a central canal carrying blood vessels that keep the tissue alive.
Inside many bones, especially at the ends of long bones and within flat bones like the pelvis and sternum, you find spongy bone. This tissue looks like a honeycomb of thin plates and bars, with small cavities between them. Despite its lighter structure, spongy bone is engineered for strength: the internal plates align along the lines of stress the bone experiences, and they can even reorganize if the direction of stress changes over time.
The cavities within spongy bone contain bone marrow. Red marrow produces blood cells: red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help blood clot. Yellow marrow, found mainly in the shafts of long bones in adults, is composed mostly of fat and holds stem cells that can become cartilage, fat, or bone tissue when needed.