Despite being bilaterally symmetric from an external viewpoint, vertebrates exhibit a significant degree of internal asymmetry, particularly regarding the formation and location of internal organs. While some of the internal organs are paired, such as the kidneys and gonads, the majority are unpaired and localized in a conserved position within the body. For example, the heart, spleen, and stomach are located on the left side of the body, while the bulk of the liver is on the right side. Even organs which appear paired, such as the lungs, are actually asymmetric; for example, in humans the right lung consists of three lobes, while the left lung has two. The organization of the internal organs allows for their efficient packing within the body cavity; it is also important for their functional development.