The lungs are paired organs located in the thoracic cavity. The surface of each lung is covered by a serous membrane (pleura).
Each lung is divided into a number of lobes and pleura, dips into interlobar fissures tissue and covers interlobar surfaces. Each lobe is sub-divided by interlobular tissue into lobules.
Each lobule is pyramidal with apex towards the hilus and base towards serous membrane Lobulations are visible as polygonal areas on the surface of lungs.
The lobulation is not so distinct in many animals, because there is less of interlobular connective tissue.
The septa of interstitial tissue contain, bronchi, vessels and nerves.
Each lobule contains the respiratory structures arising from a terminal bronchiole.
