脑(brain)
动物身体前端神经组织集中的结构。脑用以整合感觉讯息并指导运动反应，从而在维持生命所必需的本能活动中起重要作用。在高等脊椎动物，脑也是学习的中心。高等脊椎动物的脑包括後脑、中脑和前脑。後脑由延髓和桥脑组成，连接脊髓和脑的高级部分，也包含将讯息从大脑皮质传到小脑的神经细胞。在其他脊椎动物是主要感觉统合中心的中脑，在哺乳动物则主司联系後脑和前脑的作用。小脑通过大的神经束与延髓、桥脑、中脑联系。前脑包括两个大脑半球及连接两侧大脑半球、有很厚的神经纤维束组成的胼胝体；每侧大脑半球被中央沟和大脑侧裂分为四部分︰额叶、顶叶、颞叶及枕叶。占人脑大部分的大脑，与更复杂的功能有关。大脑半球的运动和感觉神经纤维在延髓交叉，分别控制的另一侧的身体。
English version：
brain
Concentration of nerve tissue in the front or upper end of an animal's body that handles sensory information, controls motion, is vital to instinctive acts, and in higher vertebrates is the center of learning. Vertebrate brains consist of the hindbrain (rhombencephalon), midbrain (mesencephalon), and forebrain (prosencephalon). The hindbrain comprises the medulla oblongata and the pons, which connects the spinal cord with higher brain levels and transfers information from the cerebral cortex to the cerebellum. The midbrain, a major sensory integration center in other vertebrates, serves primarily to link the hindbrain and forebrain in mammals. Large nerve bundles connect the cerebellum to the medulla, pons, and midbrain. In the forebrain, the two cerebral hemispheres are connected by a thick bundle of nerve fibers (corpus callosum) and are divided by two deep grooves into four lobes (frontal, parietal, temporal, and occipital). The cerebrum, the largest part of the human brain, is involved with its more complex functions. Motor and sensory nerve fibers from each hemisphere cross over in the medulla to control the opposite side of the body.