Add your arrowhead. Go to view tab and check the gridlines box. Move your arrowhead so the point is right on a grid line, if it will be okay at that spot in your slide. This will make it easier to get your line centered in the arrowhead. Otherwise you can try moving and aligning your arrowhead and your line. Now insert a line. Using custom animations you can have the line appear behind your arrowhead after it moves and then insert a second line to follow your arrowhead, etc. Another alternative, if you want to have the line physically follow your arrowhead as if it coming out of the arrowhead, use custom animation "emphasis" and assign it to "grow & shrink". Check horizontal and play with the "custom" size and placement of your line until the line seems to follow your arrowhead. Be sure your arrowhead is on top of the line. It will seem to be coming out of the arrowhead.