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n. the enlarged and highly developed mass of nervous tissue that forms the upper end of the central nervous system (see illustration). The average adult human brain weighs about 1400 g (approximately 2% of total body weight) and is continuous below with the spinal cord. It is invested by three connective tissue membranes, the meninges, and floats in cerebrospinal fluid within the rigid casing formed by the bones of the skull. The brain is divided into the hindbrain (rhombencephalon), consisting of the medulla oblongata, pons, and cerebellum; the midbrain (mesencephalon); and the forebrain (prosencephalon), subdivided into the cerebrum and the diencephalon (including the thalamus and hypothalamus). Anatomical name: encephalon.

The brain (midsagittal section).

Subjects: Medicine and Health — Science and Mathematics.

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