A normal lumbar spine has five vertebrae that start about 6 inches south of the shoulder blades, says Spine-health. They curve in toward the abdomen and are found between the thoracic spine and a triangular bone made of fused vertebrae called the sacrum, says Healthline.
The lumbar vertebrae are larger and heavier than other vertebrae, says Spine-health and Innerbody. This is because they must support the weight of the torso. The spinal cord does not travel through the lumbar spine as it does through the cervical and thoracic spine, but branches out to form the cauda equina, which means "horse's tail." These branches pass down the buttocks, down the thighs and legs and to the feet.
The vertebrae of the lumbar spine, like most vertebrae in the spine, have a spongy disk between them to cushion the bones and allow the spine to be flexible, claims Healthline. The outer layer of these disks, called the annulus fibrosus, binds the vertebrae together, says Innerbody.
The muscles that support the lumbar spine include the multifidus, the longissimus and the spinalis, says Healthline. The multifidus is a long muscle that helps the lumbar spine rotate. The longissimus begins in the middle of the lumbar spine, and the spinalis is a muscle that begins as a tendon at the sacrum and reaches up to the neck.