Central tendon of diaphragm

The central tendon of the diaphragm is a thin but strong aponeurosis situated near the center of the vault formed by the muscle, but somewhat closer to the front than to the back of the thorax, so that the posterior muscular fibers are longer.

It is situated immediately below the pericardium, with which it is partially blended.

The caval opening passes through the central tendon.

Structure
It is shaped somewhat like a trefoil leaf, consisting of three divisions or leaflets separated from one another by slight indentations.

The right leaflet is the largest, the middle, directed toward the xiphoid process, the next in size, and the left the smallest.

In structure the tendon is composed of several planes of fibers, which intersect one another at various angles and unite into straight or curved bundles—an arrangement which gives it additional strength.

Action during inspiration
During inspiration the diaphragm contracts causing the central tendon to be drawn inferiorly which partially flattens the domes. The result is an enlargement of thoracic cavity and reduction in intra-thoracic pressure. Physiologically this means that air enters the lungs and venous return to the heart is enhanced. During inspiration the central tendon retains its shape due to its tendonous nature and prevents constriction of the inferior vena cava or aorta, however the oesophagus is surrounded by muscle at the oesophageal hiatus and is constricted (food is difficult to swallow with inspiration).