matshow and origin

I am new to matplotlib and I am really impressed.
I have a problem though.

I am not able to get a lower origin in matshow, imshow gives the origin at bottom when I say origin=‘lower’

for example

#!/usr/bin/env python
from matplotlib.pylab import *

matshow(rand(64,64),fignum=100,cmap=cm.gray,origin=“lower”)
show()

will still give me origin on the top, but I want a lower one.

what do i need to do?

Thanks,
Abhi