ANATOMY
The nervous system of a fish consists of two parts: the cerebrospinal
system (as the fish is a vertebrate!) and the autonomic system.
The cerebrospinal system is divided into two divisions: the central
division, consisting of the brain and spinal cord, and the peripheral
division, consisting of both the cranial and spinal nerves and the
specialized sensing organs, such as the eyes and ears. The autonomic
nervous system consists of ganglia, fibers, and of both the
sympathetic and parasympathetic parts.
The structure of the most important organ of the nervous system, the
brain itself, may differ between different species of fish. However,
all brains contain the same definitive parts and cavities. The fish
brain consists of a forebrain, a 'tween brain, a midbrain, a
cerebellum, and a medulla oblongata. Also containing many brain
cavities such as the paired lateral ventricles, the third ventricle,
the metacoel and the fourth ventricle, the fishes brain is considered
only an enlargement of the anterior end on the spinal cord, residing
in the cranium of the skull for protection. The brain itself is
covered in a layer of blood vessels for circulation, and is whitish
and soft. Because fish are vertebrates, the posses a vertebral column
that runs the length of the fish, housing the spinal cord within the
neural canal.
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