Increasing Figure Area size

Hi you all,

I have inserted a matplotlib figure into a gtk.VBox this way:

self.Box = gtk.VBox(False, 0)
self.Figure = Figure(figsize=(8, 4), facecolor=0.92, dpi=10)
self.Box.pack_start(self.canvas, True, True)

The matoplotlib figure is inserted into the box this way...then i get a green "Frame" and a Figure area, both inside the box. However now i want to increase the matoplotlib figure area without increasing the box size...

How can i increase the figure area by decreasing the "frame" area?? is this possible??
Thanks for your answers in advance