The Diaphragm and Its Openings

• Arises from the xiphoid process (sternal part), lower six costal cartilages (costal part), medial and lateral lumbocostal arches (lumbar part), vertebrae L1 to L3 for the right crus, and vertebrae L1 to L2 for the left
• Inserts into the central tendon and is the principal muscle of inspiration.
• Receives somatic motor fibers solely from the phrenic nerve; its central part receives sensory fibers from the phrenic nerve, whereas the peripheral part receives sensory fibers from the intercostal nerves.
• Receives blood from the musculophrenic, pericardiophrenic, superior phrenic, and inferior phrenic arteries
• Descends when it contracts, causing an increase in thoracic volume by increasing the vertical diameter of the thoracic cavity and thus decreasing intrathoracic pressure.
• Ascends when it relaxes, causing a decrease in thoracic volume with an increased thoracic pressure.

1. Right crus

• Is larger and longer than the left crus.
• Originates from vertebrae L1 to L3
  
• Splits to enclose the esophagus.

2. Medial arcuate ligament (medial lumbocostal arch)

• Extends from the body of L1 to the transverse process of L1 and passes over the psoas muscle and the sympathetic trunk.

3. Lateral arcuate ligament (lateral lumbocostal arch)

• Extends from the transverse process of L1 to rib 12 and passes over the quadratus lumborum.

1. Vena caval hiatus (vena caval foramen)

• Lies in the central tendon of the diaphragm at the level of T8 and transmits the IVC and occasionally the phrenic nerve.

2. Esophageal hiatus

• Lies in the muscular part of the diaphragm (right crus) at the level of T10 and transmits the esophagus and anterior and posterior trunks of the vagus nerves.

3. Aortic hiatus

• Lies behind or between two crura at the level of T12 and transmits the aorta, thoracic duct, azygos vein, an occasionally greater splanchnic nerve.