Thank you, Mr. Goldman, for sharing this mnemonic for understanding the lengths of the parts of the hand. This has helped me more than anything I can think of to understand how the hand works and how to draw it. Knowing that the length of the fingers is half the length of the hand - and that the knuckles of the middle finger are half that, and half that again - has taught me more about the hand than anything I can think of.
Also, and not explicitly said in your breakdown - but something anyone can confirm, by placing one hand over the other at a 90 degree angle, or placing the middle finger over the back of the opposite palm - your diagram taught me that the WIDTH of the hand is half the LENGTH of the hand. This has been equally useful in setting proportions so, again, Mr. Goldman ... thank you.
-the Centaur