Dan: I don't know who has been giving you anatomy lessons on Wild Boar, but all a boar has is the same thing any mammal has, and that is a shoulder blade covering his ribs along side his shoulders. I have killed 2 wild boar, one with a .50 round ball, and the other with a 170 grain .30 cal. bullet out of a .30-30. The jacketed soft point did mushroom when it hit that 3/8 inch thick shoulder blade, and it did turn, but only after it had broken a rib on the other side, and gone through both lungs, and some of the major arteries above the heart! I don't know what that guide let his slug gun shooters use for slugs, but any foster style slug will penetrate the shoulderblade and reach the internal organs out of a 12. ga.
My best friend killed a wild boar with a .62 cal. ( 20 ga. ) rifle with a frontal shot, that sent a PRB all the way the length of the boar, where it lodged under the skin after completely penetrating the large " ham " leg muscle on the other side. He took out one lung, the top of the heart, the liver, kidneys, intestines, etc. before penetrating the ham. I think he was using 90 grains of FFg powder behind that PRB.
If you take head shots, you kill the pig with much smaller rounds to the brain. just don't aim at the centerline of the skull, and you will be okay.( a centerline hit will knock them out, and down, but just may not kill them. There is a lot of skull between the center of the eyes, and the brain.)