 Dear students, in this topic we shall discuss about the vertebrate lungs. The terrestrial vertebrates use a pair of lungs to exchange oxygen and carbon dioxide with the environment. Lungs are found in most amphibians except few ones. They are found in all reptiles, all birds and all mammals. We shall discuss about the basic plan of vertebrate lung. Although there are considerable variations among the four groups of vertebrates, the generalized structure of lung consists of a complex network of tubes and air spaces are sex. The number of air spaces per unit volume becomes progressively greater in the evolutionary order of amphibians, reptiles, birds and mammals, which means that the number of air spaces per unit volume is the lowest in amphibians, the most in reptiles and the most in mammals, where gas exchange is to take place. In comparison, the size of these terminal air spaces becomes smaller in the same order. In amphibians, the size of the air spaces is greater, whereas the size of the mammals or the LVU lye is smaller. These terminal air spaces are LVU lye make the respiratory epithelium of the lung that is thin and vascularized. So, these air spaces make the terminal a respiratory epithelium that actually functions as a gas exchange. Dear students, we shall discuss the lungs of all these four classes of vertebrates one by one. We are going to discuss amphibian lungs first. The lungs that are close to each other vary in complexity, in the case of amphibians, the lungs' complexity varies. Eurodeals lungs are just like a smooth walled pouch, which has a very smooth wall and has a bag-like and empty inside, only air sacs are present on the wall with which gas exchange happens. Frogs and toads have balloon-like lungs and septa and folds are present in these lungs which subdivide these lungs and make interconnected air sacs, through which gas exchange is comparatively a bag-like and smooth walled pouch is a better gas exchange. Dear students, the lungs of reptiles are sponge-like, they have sponge-like texture. If we remove any reptile's lung and touch it, we will feel it as if we have caught a form or a sponge. Each reptilian lung has a single bronchus which runs down the centre of the lung. Each bronchus makes branches and from these branches, individual pockets are present which go up to the periphery of the lungs. The lungs of reptiles have a single bronchus which runs down the centre of the lung. Each bronchus makes branches and from these branches, individual pockets are present which run down the centre of the lung. These pockets have gas exchange. These are the surfaces where gas exchange occurs. These pockets are similar to the alveoli in mammals. However, these pockets of reptiles are much larger and fewer in number as compared to those of mammals. Structurally similar but there are many variations in the mammals. Now we shall discuss the mammalian lungs. Mammalian lungs are more subdivided to increase the respiratory surface area. Mammals' lungs make trachea, subdivide and make bronchi. These bronchi branch repeatedly to terminal bronchioles and these terminal bronchioles divide to finally form the respiratory bronchioles. Our respiratory bronchioles are attached to a cluster of alveolar ducts with which alveolar sacs are present which make respiratory epithelium and from which gas exchange happens. Dear students, The lungs of birds are relatively smaller in size and they are connected to 7 or 9 air sacs which extend much of the body. Lungs are small in size but with them many, i.e. 7 or 9 depending on the species of birds these air sacs are attached which extend in various parts of the body and even in bones. Air sacs may be connected to air spaces within the bones. The lungs of birds have different patterns. They do not have alveolar eye but they contain millions of parabronchi. These parabrons are tiny parallel passages, tube-like passages. These are the sites of gas exchange in birds. This system enables birds to remove 90% of oxygen from the air with each breath. The mammals which have a lot of efficiency of gas exchange can remove only 25% of oxygen from the air once breathed.