The brains of all vertebrate embryos, from fish to humans, develop in the same initial steps. First, brains differentiate into three bulbs, making up the three primary structures that scaffold all vertebrate brains: a forebrain, midbrain, and hindbrain. Second, the forebrain unfolds into two subsystems. One of these goes on to become the cortex and the basal ganglia, and the other goes on to become the thalamus and the hypothalamus.
