The mitotic spindle is a structure of the eukaryotic cytoskeleton involved in mitosis and meiosis. It consists of a bundle of microtubules joined at the ends but spread out in the middle, vaguely resembling a spindle in shape, and a wire eggbeater in structure. The spindle is aligned perpendicularly to the plane along which the cell is to divide. In animal cells, the spindle is formed by the centrioles as they move apart.
Some of the spindle's microtubules attach to the centromeres of the chromosomes. They then split at the point of attachment, each half remaining attached to a sister chromatid, and pull the chromatids apart. (After being pulled apart, the chromatids are now called chromosomes.) The remaining microtubules keep the spindle rigid.