I understand that the term "umbilical cord" is typically used in reference to placental mammals, but the cord that attaches the snake's abdomen to the yolk is also commonly referred to as the umbilical cord. The umbilical cord is used to absorb the yolk through the umbilicus. Though, the umbilicus ("belly button") cannot be seen in older, healthy Ball Pythons because of growing the ventral scales.
I may be corrected if I am wrong, but this is what I have come to understand thus far and am just interested in some clarification.
Here are some threads/blog entries that refer to the Ball Python's umbilical cord.
(Graphic picture warning in the first link)
http://www.worldofballpythons.com/bl...w-belly-freak/
http://ball-pythons.net/forums/showt...y-Ball-Python.
http://ball-pythons.net/forums/showt...umbilical-cord