FoundationalConceptsNeuroscience

(fluid-filled internal spaces) in the mature brain.
If we examine the external structure of brains from various
vertebrate animals, we observe general similarities. The embryonic
forebrain, midbrain, and hindbrain regions expand in the mature
brain to contain millions of cells organized into distinct anatomical
structures. The forebrain is dominated by the cerebrum, the midbrain
by the optic tectum, and the hindbrain by the medulla and the cere-
bellum. As one moves from the evolutionarily older fish, amphibians,
and reptiles to the evolutionarily more recent birds and mammals, the
size of the cerebrum increases relative to the rest of the brain (see Figs.
2.5 and 2.6).

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Forebrain Midbrain Hindbrain Spinal cord

Figure 2.4. Basic plan of the vertebrate brain.

ta Cerebrum

Cerebrum— a ee ~< - Wy lias

eS ue a

wit. bulb oa

Spinal cord L Ch } VY ae cord

Oltactory bulls — Se Medulla

Midbrain

Figure 2.5. Brains of a fish (left) and a bird (right).

In many mammalian brains, a distinctive feature may be observed
in the structure of the cerebrum: rather than being smooth, the cere-
brum often has bumps and groves. The bumps and grooves are called