One of the most striking differences between the brains of humans and other mammals involves the size of the olfactory bulb, which is the part of the brain involved with smell. In many mammals, the olfactory bulb is a major portion of the entire brain. In fact it is present in even the most primitive vertebrates, such as fish. In humans it is a tiny little orb sandwiched between our limbic system and the bottom of our frontal lobe. This contrast illustrates our reduced reliance on the sense of smell in favor of vision, hearing, and analytic thinking, all functions supported by the cortex.