Buzz
by James Hunt
You might think you're familiar with human anatomy: the average adult has 206 bones, around 650 muscles, and roughly 18 feet of intestines. But what if we told you that’s not exactly the whole story?
It turns out there's quite a bit of variation in the body parts that most people have. You’ve likely heard of some redundant body parts, like wisdom teeth, which aren’t essential to the human body. (The appendix was once thought to be useless, but the evidence continues to build that it actually serves an immunological purpose.) But did you know there are several muscles in the same boat? Many of these muscles serve no real function, and some people—perhaps even you—don’t have them at all.
When these muscles fade away, it's simply the result of genetics: A mutation causes individuals to be born without them, and since these muscles aren't in use, you might not even notice their absence. This is why vestigial muscles tend to vanish in smaller populations. Here’s a look at what you could be missing out on.
1. OCCIPITALIS MINOR
Wikimedia Commons // Public Domain
This narrow, band-like muscle located just beneath the back of your skull allows slight movement of your scalp. Given that this particular movement isn’t particularly useful for survival today, it’s no surprise that it has disappeared in some populations. All indigenous Melanesians are born without it, along with about half of the Japanese population and a third of Europeans. Long ago, our mammalian ancestors would have used this muscle to move their ears, helping them hear predators more effectively. However, today, it serves no significant purpose, which is why it often goes unnoticed when absent.
2. PALMARIS LONGUS
Hwilms via Wikimedia Commons // Public Domain
This delicate tendon attaches to the underside of the wrist and is absent in approximately 16 percent of people, according to a recent study. It’s so weak that it doesn’t significantly impact grip strength, and if removed or severed, it won’t cause any changes in mobility. This feature makes it an excellent candidate for tendon grafts, as it can be used in other parts of the body without causing issues.
To check if you have it, extend your arm with the palm facing upward and close your hand, pressing your thumb between your middle and fourth fingers. If the tendon is present, it should protrude slightly from your wrist, much like in the photo above (though possibly less pronounced).
3. PYRAMIDALIS
Wikimedia Commons // Public Domain
Twenty percent of individuals lack the pyramidalis muscle, which is typically triangular and found in the abdomen, although most people have two. The role of the pyramidalis—tensing the linea alba—doesn’t have much of an effect; the linea alba is mainly a connective collagen structure that binds the abdominal muscles together. Unfortunately, it’s difficult to determine if you have this muscle (since it doesn’t do much), but if you undergo surgery or an MRI, you might want to ask about its presence.
4. STERNALIS
Wikimedia Commons // Public Domain
Most people don't have the sternalis muscle. It was fully documented only after a set of mammograms in the early 1990s revealed six women (out of 32,000) with an unusual structure in their chests. After surgery on one and imaging on the others, it was confirmed to be the sternalis muscle.
It’s so rare that not much is known about it. It runs vertically along the edge of the sternum, just above the pectoral muscles, but its function remains a mystery. Approximately 8 percent of humans are thought to have it, but there's no simple way to know if you're one of them. One theory suggests it could be a remnant of the panniculus carnosus—a muscle found in animals that helps control skin movement. In some animals, this allows them to ‘twitch’ their body to fend off pests or roll into a ball like the echidna.
5. PLANTARIS
Wikimedia Commons // Public Domain
Located in the leg, the plantaris muscle is around 2–4 inches long and sits at the top of the leg. It provides a slight assist in knee flexion, but not enough to make its absence problematic. If you have it, the tendon is the longest one in the human body.
Up to 10 percent of people might be missing it entirely. While its absence doesn’t cause major issues, there is a downside: The tendon is quite valuable in surgical procedures because of its length, making it a great candidate for replacing other tendons in the body. If you’re part of that 10 percent and need a tendon replacement due to injury, the donor tendon will have to come from another part of the body.
