Hey Arctic! =)
This is probably overkill, but you could build a networkx graph of the pixels of the skeleton using a variation of this recipe:
You will need every pixel of the skeleton to be its own label. You can get this by using the np.arange function and setting to zero every pixel not in the skeleton.
and then use networkx's diameter function to find the length of the longest path in the graph:
I hope that's a good enough outline to get you where you want to go! But post back to the list if you need more detail... Just a bit stretched for time right now.
Juan.