Answer:
I am heavy forward but backward I'm not.
What is black when it's clean and white when it's dirty?
I am the noise Santa's reindeers make
I jump when I walk and sit when I stand. What am I?
I fly to any foreign parts assisted by my spreading wings. My body holds an hundred hearts Nay I will tell you stranger things when I am not in haste I ride and then I mend my pace anon.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.