Develops from 4 sources
1. Septum Transversum – gives rise to Central Tendon
2. Pleuroperitoneal Membranes (Mesodermal folds) – close the connection between the thoracic and abdominal parts of the Coelom
1. Oesophageal Mesentery – also contributes to the development of the Diaphragm
2. Cervical Myotomes
  - Muscle cells derived from the 3rd, 4th and 5th Cervical Myotomes
  - Muscle cells carry their own nerve supply with them – hence the motor supply from the Phrenic Nerves
Failure of Pleuroperitoneal Membrane development – most common cause of Congenital Diaphragmatic hernia
- The defect (Bochdalek’s Foramen) is posteriorly placed
- Clinically manifests more often on left side probably due to the presence of the liver on the right
Morgagni’s Foramen – possible small hernia site at the junction of the costal and xiphoid origins

Overview

Derivative of the Inner (Transversus) layer of the muscles of the body wall
- Fibres arise in continuity with Transversus Abdominis from within costal margin
Completed behind the costal margin by fibres arising from the Arcuate Ligaments and the Crura
From circumference of oval origin, fibres arch upwards into pair of domes and then descend to a Central Tendon which lies at the level of the xiphisternal joint
- Right dome – ascends in full expiration as high as nipple line (4th space)
- Left dome – ascends as high as 5th rib
Viewed from side: diaphragm resembles inverted J – long limb extending up from Crura (upper lumbar vertebrae) and the short limb attached to xiphisternum (T8 level)
About 55% of muscle fibres (and 65% of intercostal muscle fibres) are slow twitch fatigue-resistant type

GenSurg.nz