Lower spine. X-ray of a healthy lower (lumbar) spine and part of the pelvis (bottom corners). The lumbar spine contains the five lowest unfused vertebrae (spinal bones). The vertebrae have bony projections (processes) protruding out at either side at the rear (seen faintly here). The lumbar vertebrae are thicker because they carry much of the body weight. The lowest part of the spine is a set of fused bones (sacrum) that articulates with the bones of the pelvis. The spaces (dark) between the vertebrae (white) are the intervertebral discs that act as shock absorbers.