The prosencephalon , the mesencephalon -LRB- midbrain -RRB- , and rhombencephalon -LRB- hindbrain -RRB- are the three primary portions of the brain during early development of the central nervous system .

The prosencephalon -LRB- or forebrain -RRB- , the mesencephalon -LRB- midbrain -RRB- , and rhombencephalon -LRB- hindbrain -RRB- are the three primary portions of the brain of vertebrates . They develop very early during development of the central nervous system .
