Bonus Anatomy Parts

A pal of mine has a small slit in his neck, maybe 1 or 2 millimeters wide. It’s always been there, he says, and occasionally embarrasses him by exuding a little gooey fluid. Someone once told him it was a gill (which would be appropriate enough, he says, since he was born under the sign of Pisces--and it might explain why his daughter has a passion for marine biology).

A gill? Can it truly be so? To find out, I called some anatomy experts--Dr. Michael Fishbein (chief of autopsy pathology at UCLA) and Ronald Bergman, emeritus professor of anatomy at the University of Iowa.

My pal, it turns out, has something called a branchial cleft cyst or sinus. And it is gill-related. No, he couldn’t breathe under water with it. But, in a fish, that same structure would end up as a gill slit.

From further reading we gather that all of us, as embryos, had these little clefts or indentations: four, in a row, on each side of our developing heads. Early in development, they usually disappear--all but one pair, which end up as our ear canals.

And guess what? Depending on where the opening is on the neck, it’s possible to figure out which one of the clefts didn’t close. I can’t wait to see my pal again and investigate.

Having gill-like slits is the tip of the iceberg when it comes to human variation, we learn. None of us is alike inside our bodies, which should come as no surprise, since people are plenty different on the outside. Why should variability, like beauty, be only skin deep?

Yet most anatomy textbooks don’t discuss this kind of variation, leading to many a shout of “Hey, come check this out!” in medical school dissecting rooms, says Bergman, who’s been compiling a compendium of these differences for decades. (Read about it in Bergman and colleagues’ online book, at https://www.vh.org/providers/textbooks/anatomicvariants/anatomyhp.html.)

Most variabilities don’t do us any harm--except, perhaps, when we’re under the surgeon’s knife and a vein or artery or muscle is in an odd place. Then being different can be serious.

For instance, says Bergman, more than 10% of us lack a little muscle in the wrist called the palmaris longus, and once in a while a surgeon trying to remove it will end up removing an important hand nerve instead.

Another tricky place is the liver, says Fishbein: The bile ducts can come out of it--or arteries branch toward it--in quite different places, sometimes leading to accidents during surgery.

Here are some of the other ways we can differ from each other:

* Some of us are born with little tails or extra nipples. It’s true.

* Some of us have something called “situs inversus”--kind of back-to-front bodies. Heart and stomach can be on the right instead of left; the appendix and liver on the left instead of right, etc. (This is one reason why it’s important doctors label an X-ray with “L” or “R” so they don’t inadvertently flip it back-to-front, says Fishbein.)

* Some of us are born with just one kidney--or a big horseshoe-shaped kidney instead of two separate ones.

* Some people have little extra lungs, spleens, livers and pancreases or extra lobes on those organs. The organs can be in surprising locations as well.

Veins, Bergman reckons, are the most variable of our inner body parts. Skeletons are mighty variable too. Knee bones can be of different sizes, in different positions or just plain absent. The first lumbar vertebra can have a small, rudimentary rib attached to it--in as many as 8.8% of people, according to one old study on 559 skeletons.

In the foot alone folks may have various extra or different-shaped bones, forked big toes, forked little toes, or even seven or eight toes. “Six fingers,” says Bergman, “are not uncommon.”

His Web site has a picture of a scary old device his book terms a “sixth-finger-nipper”--used by a 16th century surgeon to snip off the offending extra digit.

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If you have an idea for a Booster Shots topic, write or e-mail Rosie Mestel at the Los Angeles Times, 202 W. 1st St., Los Angeles, CA 90012, rosie.mestel@latimes.com.