Skip to main content

ACS & ASCO are Stronger Together: Cancer.Net content is now available on


Skeletal System

On this page

The skeletal system is made up of the bones that give structure to the human body. Bones protect and support vital organs and work with muscles to help the body move. Bone marrow is the soft inner part of many bones of the body.

Some of the bones in the skeletal system include the: 

  • Skull
  • Vertebrae (bones of the spine)
  • Ribs and sternum
  • Clavicle and scapula
  • Humerus, ulna and radius (arms)
  • Pelvis (hipbones)
  • Femur, tibia and fibula (legs)

The spine is made up of many vertebrae and provides the main central support for the human body. It also protects the spinal cord (nerves that go from the brain to other parts of the body) and allows flexible movement. There are 4 main sections to the spine:

  • Cervical vertebrae are those right below the skull. There are 7 cervical vertebrae. 
  • Thoracic vertebrae compose the middle part of the spine. There are 12 thoracic vertebrae, and each connects to a rib.
  • Lumbar vertebrae are the lower part of the spine. There are 5 lumbar vertebrae between the ribs and the pelvis. The lumbar vertebrae help support the weight of the body, and permit movement.
  • The sacrum is a large, triangular bone at the base of the spine and connects the spine with the pelvis (hip bones). The upper part of the sacrum connects with the last lumbar vertebra, and its lower part connects with the coccyx (tailbone).

The thorax (chest) includes a number of different bones. These include:

  • Clavicles (collar bones) which are found in the upper chest and connect the scapula and the sternum.
  • Sternum (breastbone) is a long flat bony plate in the center of the chest and connects to the upper ribs.
  • Scapula (shoulder blades) connect the humerus (upper arm bone) with the clavicle (collar bone).
  • The ribs are long curved bones which form the rib cage. The ribs surround the chest, letting the lungs expand for breathing. They protect the lungs, heart, and other organs of the thorax (chest).

The arms (not including the hands) consist of three bones:

  • The humerus is a long bone that runs from the shoulder to the elbow.
  • The radius and ulna are the two bones that run from the elbow to the wrist.

The pelvis, or hip bones, has 3 major parts:

  • Ilium (one on each side) 
  • Ischium (one on each side)
  • Pubis (pubic bone - one on each side)

The pelvis connects the spine to the lower legs and helps support the upper body

The legs (not including the ankles or feet) have three main bones:

  • Femur is the large bone in the upper leg (thigh). The longest bone in the body, the femur connects the pelvis to the lower legs at the knee joint.
  • Tibia (shinbone) is the larger and stronger of the two bones in the leg below the knee. It connects the knee with the ankle.
  • Fibula (calf bone) is the other bone that makes up the lower leg and also connects the knee to the ankle.

Bone marrow is the soft, spongy inner part of many bones. In some bones the marrow is only fatty tissue. In other bones it contains blood-forming cells. These cells make new red blood cells, white blood cells, and blood platelets.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.

Last Revised: December 13, 2022

American Cancer Society Emails

Sign up to stay up-to-date with news, valuable information, and ways to get involved with the American Cancer Society.