The crura originate from the front of the bodies and intervertebral fibrocartilage of the lumbar vertebrae. They are tendinous and blend with the anterior longitudinal ligament of the vertebral column. The right crus, larger and longer than the left, arises from the front of the bodies and intervertebral fibrocartilages of the upper three lumbar vertebrae. the left crus arises from the corresponding parts of the upper two lumbar vertebrae only. The medial tendinous margins of the crura pass anteriorly and medialward, and meet in the middle line to form an arch across the front of the aorta known as the median arcuate ligament; this arch is often poorly defined. The area behind this arch is known as the aortic hiatus.