Logic - Whenever Object Move To Locations, It Will Turn One By One ?

I have a variable called Map(19,19) is List Of Point and a Object(x,y).i want whenever my Object move to locations like Map(0,Y) or Map(19,Y) or (Map(X,0) or Map(X,19) it will turn one by one part of my Object to the other side for example when my object at location Map(0,Y) firstly, Object'head immediatetly appear at Map(19,Y) and then one by one part of it moves like that.Here my code: you can start watch from rbGeneral.checked, i already get a current position of my snake by declare 2 variables X and Y, but at If Clause i dont know put anything there to solve my trouble.

Private Sub tmr_tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles tmr.Tick
'Move Snake
Select Case currentDirection[code].......