This link from about.com has a cross section diagram of a hog's vitals. http://hunting.about.com/od/deerbigg...toshoothog.htm
Center mass is actually aft of the liver.
Note how low the heart is, below and just behind the shoulder. Hogs also have a lot of hard cartilage around the shoulder.
Good odds a bullet will have to go through upper leg bone, and possibly rib bone and / or shoulder cartilage, depending on angle.
I've seen hogs run a good distance after a "center mass" hit from a 12ga slug.
Vitals on deer are arrayed somewhat differently. http://wildgameprocessing.tripod.com/deeranatomy.html