Definition of diaphragm in Blount's 1707 Glossographia Anglicana Nova The diaphragm is an upward curved, c-shaped structure of muscle and fibrous tissue that separates the thoracic cavity from the abdomen. The superior surface of the dome forms the floor of the thoracic cavity, and the inferior surface the roof of the abdominal cavity. As a dome, the diaphragm has peripheral attachments to structures that make up the abdominal and chest walls. The muscle fibres from these attachments converge in a central tendon, which forms the crest of the dome. Its peripheral part consists of muscular fibers that take origin from the circumference of the inferior thoracic aperture and converge to be inserted into a central tendon. The muscle fibres of the diaphragm emerge from many surrounding structures and can be divided into vertebral, coastal, sternal, and from central tendon. The vertebral part of the diaphragram arises from the crura and arcuate ligaments. Right crus arises from L1-L3 vertebral bodies and their intervertebral discs. Smaller left crus arises from L1, L2 vertebral bodies and their intervertebral discs. Medial arcuate ligament arises from the fascia thickening from body of L2 vertabrae to transverse process of L1 vertebrae, crossing over the body of the psoas major muscle. The lateral arcuate ligament arises from the transverse process of L1 vertebrae and attched laterally to the 12th rib. The lateral arcuate ligament also arises from fascia thickening that covers the quadratus lumborum muscle. The median arcuate ligament arises from the fibrous parts of right and left crura where descending thoracic aorta passes behind it. No diaphramatic muscle arises from the median arcuate ligament. Both adrenal glands lie the near diaphragmatic crus and arcuate ligament. The coastal part of diaphragm arises from the lower six coastal cartilages. The central tendon of the diaphragm is a thin but strong aponeurosis near the center of the vault formed by the muscle, closer to the front than to the back of the thorax. The central part of the tendon is attached above to pericardium. The both sides of the posterior fibres are attached to paracolic gutters (the curving of ribs before attaching to both sides of the vertebral bodies). Openings alt There are a number of openings in the diaphragm through which structures pass between the thorax and abdomen. There are three large openings — one for the aorta, one for the esophagus, and one for the inferior vena cava (the caval opening), plus a series of smaller ones. The inferior vena cava passes through the caval opening, a quadrilateral opening at the junction of the right and middle leaflets of the central tendon, so that its margins are tendinous. Surrounded by tendons, the opening is stretched open every time inspiration occurs. However, there has been argument that the caval opening actually constricts during inspiration. Since thoracic pressure decreases upon inspiration and draws the caval blood upwards toward the right atrium, increasing the size of the opening allows more blood to return to the heart, maximizing the efficacy of lowered thoracic pressure returning blood to the heart. The aorta does not pierce the diaphragm but rather passes behind it in between the left and right crus. There are several structures that pierced through the diaphragm, including: left phrenic nerve pierce through the central tendon, greater, lesser, and least thoracic splanchnic nerves pierced through bilateral crura, and lymphatic vessels that pierced throughout the diaphragam, especially behind the diaphragm. + Openings through the diaphragm and their content Description Vertebral level Contents caval opening T8 The caval opening passes through the central tendon of the diaphragm. It contains the inferior vena cava, and some branches of the right phrenic nerve. The outermost wall of inferior vena cava is fused with the central tendon. esophageal hiatus T10 The esophageal hiatus is situated in the posterior part of the diaphragm, located slightly left of the west central tendon through the muscular sling of the right crus of the diaphragm.It contains the esophagus, and anterior and posterior vagal trunks, left gastric artery and veins, and lymphatics. aortic hiatus T12 The aortic hiatus is in the posterior part of the diaphragm, between the left and right crus.It contains the aorta, the thoracic duct and Azygous vein. Under the medial lumbocostal arch sympathetic trunk Under the lateral lumbocostal arch Subcostal nerve and vessels areolar tissue between the sternal and costal parts (see also foramina of Morgagni) the superior epigastric branch of the internal thoracic artery and some lymphatics from the abdominal wall and convex surface of the liver areolar tissue between the fibers springing from the medial and lateral lumbocostal arches This interval is less constant; when this interval exists, the upper and back part of the kidney is separated from the pleura by areolar tissue only. Nerve supply The diaphragm is primarily innervated by the phrenic nerve which is formed from the cervical nerves C3, C4 and C5. While the central portion of the diaphragm sends sensory afferents via the phrenic nerve, the peripheral portions of the diaphragm send sensory afferents via the intercostal (T5–T11) and subcostal nerves (T12). Blood supply alt Arteries and veins above and below the diaphragm supply and drain blood. From above, the diaphragm receives blood from branches of the internal thoracic arteries, namely the pericardiacophrenic artery and musculophrenic artery; from the superior phrenic arteries, which arise directly from the thoracic aorta; and from the lower internal intercostal arteries. From below, the inferior phrenic arteries supply the diaphragm. The diaphragm drains blood into the brachiocephalic veins, azygos veins, and veins that drain into the inferior vena cava and left suprarenal vein. Variation The sternal portion of the muscle is sometimes wanting and more rarely defects occur in the lateral part of the central tendon or adjoining muscle fibers. Development The<unk>  develops during embryogenesis, beginning in the third week after fertilization with two processes known as transverse folding and longitudinal folding. The septum transversum, the primitive central tendon of the diaphragm, originates at the rostral pole of the embryo and is relocated during longitudinal folding to the ventral thoracic region. Transverse folding brings the body wall anteriorly to enclose the gut and body cavities. The pleuroperitoneal membrane and body wall myoblasts, from somatic lateral plate mesoderm, meet the septum transversum to close off the pericardio-peritoneal canals on either side of the presumptive esophagus, forming a barrier that separates the peritoneal and pleuropericardial cavities. Furthermore, dorsal mesenchyme surrounding the presumptive esophagus form the muscular crura of the diaphragm. Because the earliest element of the embryological diaphragm, the septum transversum, forms in the cervical region, the phrenic nerve that innervates the diaphragm originates from the cervical spinal cord (C3,4, and 5). As the septum transversum descends inferiorly, the phrenic nerve follows, accounting for its circuitous route from the upper cervical vertebrae, around the pericardium, finally to innervate the diaphragm.
Thoracic diaphragm
Diaphragm 
Thoracic inlet
Boracic lint
Cervical rib
Subclavian loop
Pleural cavity
Lung cavity