Thorax and Lungs:

The  lungs, a pair of conical-shaped organs lie  in  the  thoracic cavity, protected by the bony  thorax composed of the  sternum and ribs a interiorly and ribs, scapulae and the vertebral column posteriorly. The apices of  lungs lie just  above the clavicles and  the concave base posteriorly extends to the  11^th or 12^th rib. The lung is described as having a medistinal and a costal surface. The costal surface is  in  contact with  the wall of  the pleural cavity which consist of  the  ribs and intercostals muscles  forming the  thoracic cavity. The thoracic cavity  is  lined with pleura. The pleura  is a continuous serous membrane; one surface of it  lines the inside of the rib &ge  knows as the parietal  pleura and the other surface covers the lungs knows as  the visceral pleura. The space between  the  two  surfaces is known as potential space, containing a  few milliliters of serous fluid that prevents friction between the  two surfaces. 

The  lungs are separated from each other by  the mediastinum which contains the heart and great vessels, the esophagus and, in  its upper part the trachea. The chief feature of the mediastinal  surface is  the presence of the hilum where the main  bronchus and pulmonary  artery enter and pulmonary veins leave the  lungs. Group of lymph glands which drain the  lungs are situated at the hylum and at the bifurcation of trachea. The right and  left lungs are divided by  deep fissures into lobes, the right lungs has upper, middle and lower lobes and left lung has upper and  lower. Each  lobe  is  further divided into segments. Air  is conducted to each segment through the bronchioles the  smallest branches of the bronchi.