What are flat bones?

The bones of your skeleton are classified into several categories, including flat bones. Other bone types include:

  • long bones
  • short bones
  • irregular bones
  • sesamoid bones

Flat bones are thin and flat. Sometimes they have a slight curve. Flat bones serve as a point of attachment for muscles or protection for your internal organs.

Read on to learn more about specific flat bones and their structure.

Flat bones of the skull

The bones of your skull surround and protect your brain and also provide support to your face. Many of the bones of your skull are flat bones. These include:

  • Frontal bone. This bone forms your forehead and the upper portion of your eye sockets.
  • Parietal bones. You have two parietal bones on either side of your head. They form the top and sides of your skull.
  • Occipital bone. This bone forms the back of your skull. It has an opening near the bottom that allows your spinal cord to meet your brain.
  • Nasal bones. You have two nasal bones that form the bridge of your nose. They form the bridge of your nose.
  • Lacrimal bones. You also have two small lacrimal bones that form part of your eye socket.
  • Vomer bone. This bone forms your nasal septum, the space between your nostrils.

Sternum and ribs

Your sternum is a T-shaped flat bone that’s located in the middle of your chest. It protects your heart and lungs.

Your ribs are also flat bones. You have 12 of them on either side of your body. They form a cagelike protective structure around the organs of your upper torso.

All 12 of your ribs are connected to your spine in the back. In addition, your top seven ribs attach directly to your sternum in the front. The next three ribs are linked to your sternum through cartilage. The last two ribs aren’t connected in the front and are sometimes called floating ribs.


Your scapula is a flat bone that’s commonly referred to as your shoulder blade. You have two of these triangle-shaped bones in your upper back. The muscles that allow your arms to rotate attach to your scapula.

Your scapula also joins together with your collar bone and humerus bone in your upper arm to make your shoulder joint.

Coxal bone

Your coxal bone is a large, flat bone that forms your pelvis. It’s actually made up of three bones:

  • Ilium. This is the widest part, located near the top of your pelvis.
  • Pubis. This is part that sits farthest back in your pelvis.
  • Ischium. This forms the bottom of your pelvis.

Your femur bones in your upper legs attach to your coxal bone to form your hip joint. It also provides an attachment point for several muscles, including your gluteal muscles.

Explore the interactive 3-D diagram below to learn more about flat bones.

The structure of flat bones is a little different than that of other bones, such as long bones. The different structural layers of a flat bone include:

  • Periosteum. This is the outer surface of the bone. It contains blood vessels and nerves that help provide nutrients to the bone.
  • Compact bone. This is the layer of bone below the periosteum. It’s a very hard, dense type of bone tissue.
  • Spongy bone. This is the innermost layer. It’s lightweight and helps absorb sudden stress, such as a blow to the head.

In addition, the flat bones in your skull have a unique structural feature. They meet at unique joints called sutures. Unlike your other joints, sutures can’t move. They don’t completely fuse together until your growth is complete, typically around age 20. This allows your brain to grow and expand as an infant and child.

Flat bones are a type of bone in your body. They’re typically thin, flattened, and slightly curved. Flat bones serve to either protect your internal organs or to provide a connection point for your muscles.