Dogs have umbilical cords, and they serve the same purpose in puppies as they do in human babies. The umbilical cord attaches the puppy to the mother dog's uterus, and the puppy receives oxygen and nourishment through it.
When the puppy delivers, the cord is attached to the afterbirth. The mother dog frequently takes care of the umbilical cord at birth by chewing through it, but if she does not, the person present at the birth needs to attend to the cord. The best way to perform this action is to use dental floss to tie the cord, and then cut it about 2 inches away from the puppy's body. Iodine is then applied to the severed cord area.