I really like this one, I'm a sucker for realistic biology.
The shading is good, simple but effective, the fur outlight might be a bit sketchy in places, but, being a sketch, it will do that :D
It looks like you've had a good look at some reference material, some of the lines I might suggest are too dark around the teeth, but, again as a sketch that's acceptable I feel. Maybe there could be more gradients in the shading to give more depth in the nostril and behind the teeth, but that depends on the quality of the scanner getting that across and also what hardness of pencils you had to hand ;)