Breed of dog?

Question
Hi. Maybe you can help me.
My boyfriend and I adopted a puppy. She is 4 months old.
The shelter said she was mixed with pit bull and something else.

Maybe you can recognize some other breed in her?

She has webbed toes. She is very bony. She has a round, sort of long head. She has tons of excess skin and wrinkles.
She is only 15 lbs.

Here are some pictures. I am sorry about low quality.

http://i3.photobucket.com/albums/y82/Desirai/Picture003.jpg
http://i3.photobucket.com/albums/y82/Desirai/Picture002.jpg

Answer
Looks like it might be Lab,as they have webbed toes,as well as that shape of head,they also tend to have a lot of skin when young

I can also see sighthound,such as greyhound in her as well-because she has long and skinny legs as well a the build of a greyhound

It is possible for a dog to be mixed with three or four breeds,and often they will guess a pitbull mix because of the brindle,greyhounds also have brindle

While it is possible she has pitbull in her,I would actually guess a lab/greyhound is the most likely mix,but as I said dogs can be mixed with three or four breeds,so she could still have pitbull in her,and also could possibly be boxer in there as well