-- the propatagium forms the anterior edge of the wing, and determines patterns of airflow over the wing. 

     -- the plagiopatagium provides most fo the lift.  Drag is produced when airflow over the wing tip creates vortices due to pressure differences in the upper and lower surfaces.  This structure allows the animal to safely drop large distances. 

     -- the uropatagium forms the posterior edge, between the hind legs and tail.  This section is used to modify lift and drag of the wing by moving the tail up or down.

     -- the hands form a secondary surface on the wing tip.  The palms are held perpendicular to the plane of the gliding membrane.  Digits point forward and towards the midline.  The hand orientation likely redirects airflow at the wing tip and may increase the lift to drag ratio, helping the squirrel glide greater distances.(Thorington et. al. 1998)