Flat Bone Diagram

A block cut from a skull bone, with seven parts to find.

Flat Bone Diagram

Name Date

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1 2 3 4 5 6 7
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Write the name of each numbered part.Answer key

  1. Outer compact bone
  2. Spongy bone (diploë)
  3. Inner compact bone
  4. Trabeculae
  5. Red bone marrow
  6. Periosteum
  7. Suture

Drawn for this site on 2026-09-30 from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: the parts of a long bone

All 7 parts on the diagram

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  1. Outer compact bone One of the two compact bone layers that line the spongy bone. In the skull it is also called the outer table.
  2. Spongy bone (diploë) The spongy bone between the two layers of compact bone. In the bones of the skull this layer is called the diploë.
  3. Inner compact bone The second layer of compact bone, on the inside of the skull. It is also called the inner table.
  4. Trabeculae Small bony struts that form the lattice of spongy bone. The lattice makes the bone lighter.
  5. Red bone marrow Where blood cells are made. The spaces between the trabeculae hold it.
  6. Periosteum A fibrous membrane over the outer surface of the bone. It carries the blood vessels and nerves that supply compact bone.
  7. Suture An immovable joint between two bones of the skull. Dense fibrous tissue fills it. It follows a twisting line, not a straight one.

How this list was compiled: Every name and detail checked on 2026-09-30 against OpenStax Anatomy and Physiology 2e, section 6.3 Bone Structure (flat bones as a layer of diploë, spongy bone, lined on either side by compact bone; periosteum; trabeculae and red marrow of spongy bone), https://openstax.org/books/anatomy-and-physiology-2e/pages/6-3-bone-structure, section 6.2 Bone Classification (examples of flat bones) and section 7.2 The Skull (sutures), and against Wikipedia, text only: Flat bone, Diploë, Periosteum, Trabecula and Fibrous joint. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Licence: own work

How it works

A flat bone is a sandwich: spongy bone between two layers of compact bone. This block is cut from the roof of the skull and holds the anatomical parts of a flat bone that a course asks for.

Read the full guide

Read the cut face from the top

Numbers 1 to 3 are the sandwich: compact bone on the outside, spongy bone in the middle, compact bone on the inside. Numbers 4 and 5 look closer at the middle layer: the struts of bone and what fills the spaces between them. Number 6 is the membrane on the outer surface, and number 7 is the joint where this bone meets the next.

  • In a skull bone the spongy layer has a name of its own: the diploë.
  • Compact bone is the bread of the sandwich and spongy bone is the filling.

Questions and answers

What are the parts of a flat bone?

Two layers of compact bone with a layer of spongy bone between them. The spongy bone is a lattice of trabeculae with red bone marrow in its spaces, and a periosteum covers the outer surface.

What is the diploë?

The spongy bone in the middle of a flat bone of the skull, between the outer and inner layers of compact bone.

How is a flat bone different from a long bone?

A long bone has a shaft round a medullary cavity and an epiphysis at each end. A flat bone is thin and often curved, built as a sandwich of spongy bone between two layers of compact bone.

What are examples of flat bones?

The bones of the skull roof, the shoulder blades (scapulae), the breastbone (sternum) and the ribs. Flat bones protect the organs behind them and give muscles a place to attach.

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