I was looking at my wrist and I just want to make sure I am following you. The wrist cephallic would be more on the "top"/ "side" part of your wrist than the bottom correct? I ask because the vein (i think it is an artery) that comes from the the bottom (underside) of my wrist and then goes up the back side of thumb, I can detect a pulse in, and it is also the stereotypical place to feel for a pulse on someones wrist so I assume this is not the "vein" you are describing but rather an artery.
The vein I think you are describing is more towards the top/side of my wrist, and if i follow it toward my thumb, it seems to actually go to the "V" between my thumb and index, then possibly forks but definitely veers right along my thumb. If I'm looking at my LEFT hand as i type it is on the right hand side of my wrist, just a little bit above the actual side point of my wrist (where there is a little "point"), and I cannot detect a pulse in it, which is a good sign I know. It is very superficial and i can feel it under my skin.
As a side note, how worried does one have to be about hitting an artery in the backs of one's hands? There seem to be many bulging veins back there that I could easily hit, but I just like to be cautious. Additionally, what do you think about shooting into the tops of ones feet? Kind of the same question as the hands, but with feet. I hear that you should avoid feet, if your arms and hands are accessible and not collapsed, true?