animating path's width

i have a path like this

var r = Raphael('graph', 600,400);
var l = r.path('M  300,185 L 75,185开发者_Go百科 Q  65,200  75,215 L  300, 215 Z');

i want the path to animate to final position

var l1 = r.path('M  350,185 L 75,185 Q  65,200  75,215 L  350, 215 Z');

Its a rectangle but curved from left side. I want to animate its right side to left/right. How i can do this in raphael.js?

var r = Raphael('graph', 600,400);
var l = r.path('M  300,185 L 75,185 Q  65,200  75,215 L  300, 215 Z');
l.animate({path : 'M  350,185 L 75,185 Q  65,200  75,215 L  350, 215 Z'}, duration);

I guess.