Left lateral view of lumbar vertebrae and associated spinal nerves. The bodies of lumbar vertebrae are massive to support the body's weight. They are bound to one another by fibrocartilagenous intervertebral discs (symphysis joints). Zygoapophyseal or facet joints are synovial joints between superior and inferior articular processes between vertebrae. The intervertebral foramen is where spinal nerves exit the vertebral canal. The pars interarticularis is a region or bridge of bone between the superior and inferior articular processes. Defects in that region are referred to as spondylolysis. The transverse processes are directed posterolaterally and spinous processes of lumbar vertebrae are broad and blunt and project posteriorly and nearly horizontally. Both serve as muscle attachment sites for deep back muscles. In the lumbar spine, nerves exit inferior to the vertebra from which they are numbered.  (Image courtesy of AL Rhoton, Jr.)