Definition: "Organ that is the center of the nervous system. It is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing, balance, taste, and smell. It appears when the neural tube segregates in forebrain, midbrain, and hindbrain at NF stage 22. The general pattern of the brain has been mainly established at NF stage 28. Yolky material is consumed and the fibre tracts and later the commissures develop. In general all of its parts are well developed at NF stage 53 and later development consists mainly of growth and some further cytological differentiation. In the period of metamorphosis only topographical changes take place."
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