Siamese triplets are either triplets that are born in the region of Siam or triplets that are born joined together. Triplets that are both born in Siam and are joined together are referred to as "Super Siamese Triplets". This article deals mainly with the Siamese triplets that are joined.
There are many possible configurations of Siamese twins. In fact, the number of possible configurations for a Siamese -tuplet is an unsolved problem in mathematics. If someone were to solve this problem they would instantly become world famous. What will be revealed here is an incomplete solution based empirically on biological evidence and not on theoretical mathematics.
edit Three Headed Giant
Most accounts depict the "Three Headed Giant" as sharing one torso and one pair of legs. The THG form appeaers homicidal but is actually harmless due to the arguments that always develop between the brothers or sisters in the triplet.
Inevitably two of the heads gang up on the third, but since the giant cannot act unless all three heads cooperate the murderous impulses of the giant go unrealized.
The Lovecraftian form takes it's name from its nightmarish, eldritch appearance. It shares a torso, two pairs of arms and one leg. It moves around on it's belly, dragging its leg behind it. It's three mouths hoover up any matter left lying on the ground.
Unfortunately these creatures often perish after choking on beer cans, garbage bags, sidewalks, or hubcaps which they accidentally suck up along with their preferred food, Cthullu droppings.
The only recorded sighting of these specimens took place in some dump called Dunwich.
A Star triplet is joined at the head. It can run at speeds of up to 100 mph by performing a kind of rapid cartwheel using its six legs. Star triplets are very intelligent since their brain is three times the normal size.
Sadly, not many stay as Siamese triplets as they are always separated when they stop cartwheeling. The operation to separate these triplets is very difficult as it involves tripartite brain surgery. Most surgeons prefer a chemical-induced separation: a small hole is created at the junction of the three brains, a dynamite stick inserted, and the triplets blown apart. The triplets of course do not survive but the operation is quick and easy.
edit Famous siamese triplets
Oscar Wilde was actually a siamese triplet. He belonged to a very common configuration where the triplets all share one pair of arms, one pair of legs, one torso and one head.