The structures in the mediastinum are covered by loose connective tissue and it also lines the internal surface of the thoracic cavity. In order to form definite fibrous layers, it is condensed within certain areas. A continuous fibro-elastic membrane known as the endothoracic fascia is created by the condensation at the internal surface of the thoracic cavity.
Two planes of cleavage can thus be demonstrated after this fascia divides the parietal pleura through the walls of the thoracic cavity.
- An extrapleural plane amongst the pleura along with the endothoracic fascia.
- An extrafascial plane amongst the fascia as well as the walls of the cavity.
The endothoracic fascia consists of inconsistent quantities of fat. Over the heads of the lungs it becomes more fibrous as the suprapleural membrane. It divides internal mammary artery from the pleura.