Subject: Why isn't the cresent of the moon perpendicular to the sun?

I understand what causes the different phases of the moon, however I 
sometimes motice that the angle of the cresent isn't always 
perpendicular to the direction the suns rays appear to come from. I 
would expect to be able to draw a line between the two 'points' of a 
cresent and then have a line perpendicular to that point directly at 
the sun, but this does not appear to be the case.
Is this due to my latitude? or perhaps to the incline of the moons 
orbit around the earth?
I can't seem to make sence of it, but it is definately true.
Your help is very much appreciated in this matter.

Re: Why isn't the cresent of the moon perpendicular to the sun?