Diaphragm

The diaphragm is a very large and flat, domeshaped, aponeurosis muscle that completely separates the thoracic cavity from the abdominal cavity. From its thoracic side, the diaphragm is highly convex, while its abdominal side is concave.

Origin: Lumbar vertebrae

Insertion: Inner side of ribs and costal cartilage and dorsal side of xiphoïd cartilage

Rapport: Between the thorax and the abdomen

Action: Inspiration

Vascularization: Aorta, phrenic arteries and veins, caudal vena cava, azygos and hemiazygos veins, esophageal vessels

Innervation: Phrenic nerves

Description:

The diaphragm originates on the ventral side of the lumbar vertebrae from two, right and left, tendons, sometimes common, from which emerge the corresponding crura. From there, radiated bundles of muscles begin, which gather to the central tendon and end in digitations that attach to the inner side of the ribs, costal cartilage and dorsal face of the xiphoid cartilage.

This muscle is composed of a aponeurotic central tendon and muscular fibers that can be organised into 3 parts:

• A lumbar part, composed of the left and right crura (they prolongations are sometimes referred to as “intermediate crura”)

• A costal part

• A sternal part

It is also pierced by three openings which allows the path to different structures:

• The aortic hiatus, for the aorta, azygos and hemiazygos veins, thoracic duct

• The oesophageal hiatus, for the oesophagus,vagal trucks

• The caval opening, for the caudal vena cava

The diaphragm is involved in the inhaling process, when it contracts itself, its volum increase facilitating the air entry inside the lungs.

Variation:

The main variations appear between Humans and carnivores and ungulates.

In humans and carnivores, the peripheral muscle fibers are wider and the two tendons initiating the lumbar part of the diaphragm are distinctly dissociated and linked by a thin fibrous blade.

In ungulates, the muscle fibers are a lot thinner and the two tendons which almost make one are blended with the ventral longitudinal ligament.

Depending on the species, the “intermediate crura” are more or less distinct.

Additionally, the central tendon of humans is highly trifoliated in contrast to the one of domesticated mammels.