Lower jaw?

I'm making a balaclava based fursuit head but i'm not quite sure on how to foam the lower jaw. I have the top part done and i'm quite proud as it's my first foaming experience (besides for a failed attempt at a bucket head base, I didn't even try making a mouth). It's not a moving jaw, by the way, just 'toony.

Can anyone help me with how to shape a lower jaw?
Also, I have more of an idea on how to make the eyebrows/cheeks but if anyone has tips I'll take them!

(I can add pictures if needed)