All of the following are true about Sibson's fascia except

Ref. Gray’s anatomy.  41st edition. Page. 446,896. Topic, Subtopic – Thorax, fascia Sibson's Fascia: The suprapleural membrane, also known as Sibson fascia, is a dense fascial layer that is attached to the inner border of the first rib and costal cartilage anteriorly, C7 transverse process posteriorly and to the mediastinal pleura medially. It is flat and lies in the oblique plane of the thoracic inlet, with a cervical dome of pleura attached to its under surface. Lying on it are the subclavian vessels and other structures in the root of the neck. The function of the membrane is to provide rigidity to the thoracic inlet that prevents distortion due changes in intrathoracic pressure during respiration.