Quote - It would have helped if you had the displacement expanded so that we could see it.

I'll guess that the veins are light grey on a darker grey background.  You need a black background.  Try running the displacement map to a math function node (subtract) and subtract 0.5 or whatever it takes to just reach a black background.  Run this output to another math node to take the square root to restore some dynamic range.  Run that output to the root shader node's displacement input.

That's right, I posted that Screen Capture, and my displacement  is black Background with veins in white and shades of gray, that's how the displacement map must be to work this way, and the veins map must be plugged to the displacement channel not the bump