This excellent page on the Washington State Department of Natural Resources has a beautiful PDF map of the landforms created by the Cordilleran Ice Sheet. It also has an interactive slide show that illustrates the retreat of the ice sheet.
And since the latter current escapes from the arm by the opening made in one of the veins, there must of necessity be certain passages below the ligature, that is, towards the extremities of the arm through which it can come thither from the arteries.