Left crus of diaphragm

The left crus of the diaphragm is a muscular structure that originates from the lumbar vertebrae. It arises from the anterolateral surfaces of the superior three lumbar vertebral bodies and the intervertebral discs, merging with the anterior longitudinal ligament. The left crus is tendinous at its vertebral attachment and becomes fleshy as it fans out proximally to merge with the diaphragm proper.

The right crus is larger and longer than the left crus, arises from the anterior surfaces of the bodies and intervertebral fibrocartilages of the upper three lumbar vertebrae, while the left crus arises from the corresponding parts of the upper two only. The medial tendinous margins of the crura pass forward and medialward, and meet in the middle line to form an arch across the front of the aorta called the median arcuate ligament (this arch is often poorly defined).