Irregular Bones

Irregular bones, as their name suggests, have unique and varied shapes. They have an outer layer of compact bone and an inner layer of spongy bone. One example of irregular bones is the vertebrae in the spinal column.

As seen in figure 1, part of the vertebra is called the body. The bodies of different vertebrae are stacked on top of each other to make the spine. Due to the tremendous force that goes through the spine, these vertebrae need to be able to withstand a lot of force coming from different directions. This is achieved by the inclusion of spongy bone in the composition of the vertebra. Also, on top of each vertebral body, there is a layer or disc of fibrocartilage, which allows for further shock absorption.

Dorsal to the body, there are pedicles which are where the ribs attach and rotate. In between the pedicles, there is an opening in the vertebra called the vertebral foramen, where the spinal cord runs through.

The vertebrae can have horns or processes, depending on where in the spinal column they are located. These are needed for muscle attachment and allow for rotation, bending, and other movements. For example, the spinous process prevents the back from bending too far backward.

Figure 1: A vertebra found in the spine.