Ah, I stand corrected:) Maybe a better diagram might be to merge our ideas:

Fish Brain = brain stem + pallium + other parts of brain[1]

      |
 (evolved into)
      |
      V

Human Brain = brain stem + gigantic cortex(which directly evolved from the pallium) + other parts of brain[1]

Good to know:)

[1] Am using "other parts of the brain" to cover any parts of the brain not covered by the brain stem and cortex