Joined at the hip. Really.

In a development that will delight John to no end, doctors in L.A. are currently working to separate a set of conjoined twins:

The complex surgery on Regina and Renata Salinas Fierros began at about 6 a.m. at the Childrens Hospital Los Angeles. About 80 doctors and staff members will try to separate many of the girls' vital organs. The girls, whose parents are from Mexico, are considered ischiopagus tetrapus twins, which doctors at the hospital said are among the rarest and most complex to separate because they share many organ systems. The twins are fused on their front, and today doctors will attempt to separate their liver, intestine, urinary, reproductive, vascular and musculo-skeletal systems.

And in a development that will irk John to no end, I'm going to post some facts about ischiopagus tetrapus twins before he gets the chance:

* Ischiopagus tetrapus twins are extraordinarily rare -- they make up about 6 percent of conjoined-twin births, which themselves only occur at a rate of 1 in 50,000. So, Will, your wife has about a .00012 percent chance of giving birth to babies like Regina and Renata next month. (I suppose you could argue that she has a 0 percent chance, as she's not actually carrying twins, but, you know.) They're not the rarest kind; that honor goes to "craniopagus" twins, who share brains and make up just 2 percent of conjoined twins.

* Two sets of female ischiopagus tetrapus twins were born in 1977 and successfully separated at the St. Louis Children's Hospital in the following year. It's no coincidence that both sets (and the set having surgery today) are female; about 70 percent of conjoined twins are. Nobody knows why.

* What is an ischiopagus tetrapus twin, anyway? "Tetrapus" simply means the twins have the proper number of legs. If they're born with three legs, they're "tripus." As for "ischiopagus," it's a big word that simply means the twins are connected at the ischium, or the lower part of the pelvis.