The bones on either side of the waist are called the iliac bones. If the patient is in the prone position, a bony prominence, called the posterior superior iliac spine, can be palpated about five centimeters on either side of the waist. This bony prominence is called the posterior superior iliac spine. In the prone position, a depression can be seen on the medial side of the posterior superior iliac spine and on both sides of the spine, also called the lumbar eye. In the standing position, a bony prominence can be palpated on both sides of the waist, and the highest point of the bony prominence is called the highest point of the iliac crest. The highest point of the iliac crest is generally flattened between the spinous processes of the fourth and fifth lumbar vertebrae, and this highest point of the iliac crest is usually used as an anatomic point for clinical localization of the spinous processes of the lumbar vertebrae. The line connecting the highest points of the iliac crests on both sides, just passing through the fourth and fifth spinous process interval, and so on can be extrapolated to the sacrum and the first, second, third, and fourth vertebrae.