Components of the Skeleton

Overview of the Human Skeleton

The human skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton. Each part contains specific bones and serves distinct functions in support, movement, and protection.

• Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage. It forms the central axis of the body and protects vital organs such as the brain, spinal cord, and heart.

• Appendicular Skeleton: Includes the bones of the limbs and girdles (pectoral and pelvic). It is responsible for movement and interaction with the environment.

Additional info: The axial skeleton contains 80 bones, while the appendicular skeleton contains 126 bones.

Bone Markings

Bones have various markings that serve as sites for muscle and ligament attachment, surfaces involved in joints, and passages for nerves and blood vessels. Understanding these markings is essential for identifying bone features and their functions.

• Sites of Muscle or Ligament Attachments:

  • Tuberosity: Large rounded projection; may be roughened.

  • Crest: Narrow ridge of bone; usually prominent.

  • Trochanter: Very large, blunt, irregularly shaped process (found only on the femur).

  • Line: Narrow ridge of bone; less prominent than a crest.

  • Tubercle: Small rounded projection or process.

  • Epicondyle: Raised area on or above a condyle.

  • Spine: Sharp, slender, often pointed projection.

  • Process: Any bony prominence.

• Surfaces Involved in Joints:

  • Head: Bony expansion carried on a narrow neck.

  • Facet: Smooth, nearly flat articular surface.

  • Condyle: Rounded articular projection.

  • Ramus: Armlike bar of bone.

• Passages for Nerves and Blood Vessels:

  • Fossa: Shallow, basinlike depression in a bone, often serving as an articular surface.

  • Sinus: Cavity within a bone, filled with air and lined with mucous membrane.

  • Meatus: Canal-like passageway.

  • Foramen: Round or oval opening through a bone.

  • Fissure: Narrow, slitlike opening.

Skull Anatomy

The Four Views of the Skull

The skull can be examined from four primary perspectives to understand its structure and the arrangement of cranial bones:

• Lateral View: Shows the side of the skull, highlighting the temporal, parietal, and sphenoid bones.

• Superior (Top) View: Displays the arrangement of cranial bones from above, including the frontal, parietal, and occipital bones.

• Anterior (Front) View: Reveals the facial bones, orbits, and nasal cavity.

• Posterior (Back) View: Shows the occipital bone and lambdoid suture.

Cranial Bones

The cranium is composed of several bones that protect the brain and form the structure of the head. The major cranial bones include:

1. Frontal bone

2. Parietal bone (left and right)

3. Temporal bone (left and right)

4. Occipital bone

5. Sphenoid bone

6. Ethmoid bone

Additional info: The cranial bones are joined by immovable joints called sutures.

Sutures of the Skull

Sutures are fibrous joints that connect the bones of the skull. The major sutures include:

• Coronal suture: Between the frontal and parietal bones.

• Sagittal suture: Between the two parietal bones.

• Lambdoid suture: Between the parietal bones and the occipital bone.

• Squamous suture: Between the parietal and temporal bones.

Table: Classification of Bone Markings

The following table summarizes the classification and function of common bone markings:

Stop and Think!

It is helpful to look up the meaning of bone names to better understand their location and function. Many bone names are derived from Latin or Greek and describe their shape or position.