Beginning and ending of joints betwwen components

Hi all,

I am creating a new script which detects joints between several components and identifies the start node and the end node. I show an example in the image below:

I am able to detect all joints with the *findmark command, but I don't know how to identify the node which 'starts' or 'ends' the joint. The start/end nodes are those which have temp nodes in the image.

Can anyone help me to do this? Any suggestion?

Thanks in advance,

Alex