An terior cerebral artery A1 segment hypoplasia is an uncom-. mon fetal variant of the circle of Willis. The frequency of this. congenital variation is 1â13% as derived from angiograms. and autopsy reports. Impaired collateral blood flow through. the circle of Willis is a recognized risk factor for ischemic. stroke. The A1 segment of the anterior cerebral artery is a. principal supplier of anterior collateral blood flow.
George Washington, 1799. Printer Friendly Version >>>. George Washington finished his second term as the first President of the United States in 1797. Weary of the political infighting surrounding the presidency, he longed for the peace of retirement to his beloved Mount Vernon.
Biography of George Washington. George Washington â first American president, commander of the Continental Army, president of the Constitutional Convention, and gentleman planter. These were the roles in which Washington exemplified character and leadership. Learn more about the remarkable life of George Washington in our biography below.