Development of septum transversum and diaphragm

Septum transversum

It is a thick mass of mesoderm which partially separates thoracic cavity and abdominal cavity.

  • Forms in neck by fusion of 3, 4, 5 cervical myotomes
  • Motor nerve is phrenic nerve
  • Embryonic disc folds and heart descends, therefore septum transversum is pushed caudally and pulls the phrenic nerve with it


  1. Superior layer – formation of fibrous pericardium
  2. middle layer – diaphragm muscle, central tendon, diaphragmatic pleura and peritoneum
  3. Inferior layer – fibrous capsule and connective tissue of liver, ventral mesentery of the gut



Origin: Mesoderm

Diaphragm develops from:

  1. Septum transversum – Central tendon, sternal and costal parts of diaphragm
  2. 2 pleuro-peritoneal membranes – 2 mesodermal folds that project inwards from body wall. Close pleuro-peritoneal canals. Forms dorsilateral part of diaphragm
  3. Mesoderm from chest wall – marginal part of diaphragm
  4. Mesentery of esophagus – Posterior medial part and crura of diaphragm
  5. Mesoderm around aorta – lumbar part of diaphragm


Image result for development of diaphragm

Congenital anomalies:

  1. Parasternal hernia of Morgagni – failure to develop a small part of diaphragm between sternal and costal part
  2. Esophageal hernia – Protrusion of stomach in thorax
  3. Congenital diaphragmatic hernia of Bochdalek – failure of pleuro-peritoneal membranes to close the pleuro-peritoneal canals. Abdominal vicera enter pleural cavity, compress heart and lungs

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