The lumbar vertebrae are a group of five individual bones of the spinal column. Together they form the lumbar region, which is one of five different regions in the vertebral column or backbone. They make up the inward-curving portion of the spine in what is commonly called the small of the back. The entire adult spinal column is composed of 26 individual bones, called vertebra when singular, and vertebrae when plural. The lumbar vertebrae are more robust than the vertebrae of the other regions, as they are responsible for bearing the weight of the body above them, and anything held or carried.
The lumbar vertebrae share the basic characteristics of all vertebrae. These include the body, a flat, disk-like part of the bone that faces the front of the torso. Behind the body there is a hole called the vertebral foramen, through which the spinal cord passes, and which is enclosed by the vertebral arch. Two pedicles join the arch with the body, which are opposite two individual lamina on the vertebral arch. The vertebral arch also has three processes, in this case three small projections, to which muscles are attached. Two projections above and below each side of the arch, called the superior and inferior articular processes, form joints with the two nearest vertebrae.
As the lumbar vertebrae bear more stress than other vertebral regions, they have some unique characteristics that allow them to support the trunk of the body. The bodies of the lumbar vertebrae, which are the weight bearing portions of all vertebrae, are broader and larger than bodies in other regions. The three projecting processes are short and blunt to allow for the attachment of large, strong muscles. The articular processes also face different directions, providing more stability in the lumbar region by limiting the range of rotation.
The lumbar vertebrae are labeled similarly to other vertebrae in the spinal column. They are designated by a letter, in this case L for lumbar, and a number based on their order in the column. The lumbar vertebra nearest the head is termed L1, proceeding in descending order to the lowest, L5.
To identify the lumbar vertebrae as individual bones, one must know how they differ from the vertebrae of the two regions above them, called the cervical and thoracic regions. Cervical vertebrae have two holes in the arch, and thoracic vertebrae have facets where the ribs are attached. Lumbar vertebrae have neither characteristic, and their larger, thicker bodies are also identifying markers.