The Medulla Oblongata is the primitive area of the brain responsible for regulating life-sustaining bodily functions (breathing, heart rate, etc.), and is the center of basic instincts. Sometimes referred to as the "reptilian" brain, the medulla oblongata is analogous to the brains of the most primitive animals. The modern human brain evolved from this simple organ into the complex system it is today.
The medulla oblongata is located directly between the brain stem and the rest of the brain.