_Tr._, Trachea; _S_, left brachial artery; _B_, brachiocephalic
artery; _l.g._, lymph gland. Pleura indicated by red line.
]
The =parietal pleura= (Pleura parietalis) lines the cavity in which each
lung is situated (Cavum pleuræ). On the lateral thoracic wall it is
adherent to the ribs and intercostal muscles and is termed the =costal
pleura= (Pleura costalis). Behind it is closely attached to the
diaphragm, forming the =diaphragmatic pleura= (Pleura diaphragmatica).
The part which is in apposition with the opposite sac or covers the
mediastinal organs is termed the =mediastinal pleura= (Pleura
mediastinalis); where this layer is adherent to the pericardium, it is
distinguished as =pericardiac pleura= (Pleura pericardiaca).[126]
The pleura is reflected at the root of the lung, which it covers,
constituting the =visceral= or =pulmonary pleura= (Pleura pulmonalis).
Behind the root of the lung a considerable triangular area is not
covered by the pleura, the two lungs being attached to each other by
connective tissue in this situation.
The =ligament of the lung= (Lig. pulmonale) is a fold formed by the
reflection of the pleura from the mediastinum and the diaphragm to the
lung, behind the triangular area of adhesion just mentioned. It is seen
when the base of the lung is drawn outward. It contains elastic tissue,
especially in its posterior part.
[Illustration: