I am not particularly knowledgeable about wild pigs, but I do know that it is not a spot ON the hog, but IN the hog.
This article might prove useful.
http://www.texasboars.com/anatomy.html
I cannot vouch for them, but these guys seem to know what they are talking about
http://forum.gon.com/showthread.php?t=429672
Good luck on your hunt.
Lost Sheep