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. From this series of origins the fibers of the diaphragm converge to be inserted into the
central tendon. The fibers arising from the
xiphoid process are very short, and occasionally
aponeurotic; those from the medial and
lateral lumbocostal arches, and more especially those from the ribs and their cartilages, are longer, and describe marked curves as they ascend and converge to their insertion. The fibers of the crura diverge as they ascend, the most lateral being directed upward and lateralward to the central tendon. The medial fibers of the right crus ascend on the left side of the
esophageal hiatus, and occasionally a fasciculus of the left crus crosses the aorta and runs obliquely through the fibers of the right crus toward the
vena caval foramen. ==References==