A few of the fibers of pyramidal tract do not cross to the opposite side in the medulla but pass ipsilaterally down the cord in the ventral coicospinal tracts. Many, if not most, of these fibers, eventually cross to the opposite side of the cord either in the neck or in the upper thoracic region. These fibers may be concerned with control of bilateral postural movements by the supplementary motor coex.The supplementary motor area tends to produce bilateral motor responses when stimulated. The other areas would tend to produce unilateral responses.Ref: Guyton; 13th edition; Chapter 56; Coical and Brain Stem Control of Motor Function