The crus of diaphragm (pl. crura), refers to one of two tendinous structures that extends below the

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

to the

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...

. There is a right crus and a left crus, which together form a tether for muscular contraction. They take their name from their leg-shaped appearance – ''

crus Crus can refer to: *''Crus'', a subgenus of the fly genus ''Metopochetus'' *Crus (lower leg) *Crus, a plural of Cru (wine) *CRUs, an abbreviation of Civil Resettlement Units * Rektorenkonferenz der Schweizer Universitäten (CRUS; English: Rectors' ...

'' meaning ''leg'' in Latin.

Structure

The crura originate from the front of the bodies and

intervertebral fibrocartilage An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold t ...

of the

lumbar vertebrae The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...

. They are tendinous and blend with the

anterior longitudinal ligament The anterior longitudinal ligament is a ligament that runs down the anterior surface of the spine. It traverses all of the vertebral bodies and intervertebral discs on their ventral side. It may be partially cut to treat certain abnormal curvatur ...

of the

. * The ''right crus'', larger and longer than the left, arises from the front of the bodies and

intervertebral fibrocartilages An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold t ...

of the upper three

. * 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 The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...

known as the

median arcuate ligament The median arcuate ligament is a ligament under the diaphragm that connects the right and left crura of diaphragm. Structure The median arcuate ligament is formed by the right and left crura of the diaphragm. The crura connect to form an ar ...

; this arch is often poorly defined. The area behind this arch is known as the

aortic hiatus The aortic hiatus is a hole in the diaphragm. It is the lowest and most posterior of the large apertures. It is located approximately at the level of the twelfth thoracic vertebra (T12). Structure Strictly speaking, it is not an aperture in th ...

. 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 The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Both ...

are very short, and occasionally

aponeurotic An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join musc ...

; those from the medial and

lateral lumbocostal arch The lateral arcuate ligament (also lateral lumbocostal arch and external arcuate ligament) is a ligament under the diaphragm that arches across the upper part of the quadratus lumborum muscle. It is traversed by the subcostal nerve, artery and vei ...

es, 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 In human anatomy, the esophageal hiatus is an opening in the diaphragm through which the esophagus and the vagus nerve pass. Structure It is located in the right crus, one of the two tendinous structures that connect the diaphragm to the s ...

, 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 The thoracic diaphragm, or simply the diaphragm ( grc, διάφραγμα, diáphragma, partition), is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. The diaphragm is the mo ...

References

External links

* - "The abdominal surface of the diaphragm." Ligaments of the torso Thoracic diaphragm {{Portal bar, Anatomy