These Are the Body Parts You Didn't Even Know You Had

We all know our "heads, shoulders, knees, and toes." But what about our plantaris, palmaris longus, and auriculars? No, those aren't made-up words from Harry Potter or Lord of the Rings. They're actual body parts.

Yes, for most of us, the body is host to a whole bunch of secrets. Some, you may have seen and simply not registered as its own thing. (Exhibit A: That weird tendon in your wrist.) But others, like a previously undiscovered corneal layer, are totally new—and elusive. So, without further ado, here's a roundup of the most little-known body parts. Whether it's due to their size, their uselessness, or their indeterminacy, these body parts have escaped knowledge writ large for far too long.

1. The Lacrimal Punctum

Colloquially known as the "eyelid hole," this is a small cavity at the bottom and top corner of your eyelids which can be found if you look closely. While everyone has one, the hole can vary in size depending upon the person. According to the Cleveland Clinic, its usage is to help drain some of your eye's excess tears, funneling it into the back of your nose (hence the runny nose when you cry). In some cases, the lacrimal puncta can malfunction and work backwards, allowing individuals to squirt liquids from their eyes.

2. Jacobson's Organ

Also known as the vomeronasal organ, this organ is a cluster of sensory cells found within the main nasal chamber of most amphibians, reptiles, and mammals. Its use is to detect moisture-borne odors such as pheromones to communicate non-verbally, particularly in matters of romance and sexuality. Due to a lack of proper receptors in humans, however, the organ is considered by most to be non-functional, a vestige of an earlier time.

The discovery of the Dua layer serves to perform simpler eye operations.

3. The Mesentery

The mesentery is a fold of tissue located within the gut which connects the stomach, intestines, pancreas, spleen, and other internal organs to the abdomen. Until recently, however, the mesentery was considered to be a collection of disparate membranes. It wasn't until research published in 2016 in The Lancet that it was deemed to be a singular, continuous organ. As a result, further research into the still largely-unknown body part should be forthcoming in the near future.

4. The Philtrum

In most mammals—such as your dog—the philtrum is a tiny slit near the nose which allows odor molecules collected on the nose to filter either into the mouth or into the aforementioned vomeronasal organ. In humans, however, the philtrum has ceased to play such a role, and now simply remains as the cute indented groove between your nose and mouth. An abnormal philtrum, meanwhile, can signal the presence of autism or fetal alcohol syndrome.

5. The Auricular Muscles

The auricular muscles are a collection of three littleknown muscles on the outside of the ear. While in other mammals these muscles can be used to tilt the ear towards sounds of interest, humans have largely ceased to be able use them. Instead, they simply turn their heads. Some people can, however, with practice, regain functioning their functioning—providing an excellent parlor trick for years to come.

6. The Palmaris Longus

The palmaris longus tendon is a slender muscle found in the middle of the wrist. While many distant mammalian relatives, such as the orangutan, still employ the muscle, it is has become vestigial both in humans and our closest primate brethren such as the chimpanzee. As a result, it's actually absent in about 15 percent of the population. To tell if you have one or not, pinch your fourth finger to your thumb and flex your wrist. If present, a vertical line will bulge beneath the skin. Fortunately, it's absence appears to have little effect on the ability to grip.

7. Dua's Layer

Discovered in 2013, Dua's layer is a previously-unknown layer of membrane on the cornea. Estimated to be about 15 micrometers thick, and lying between two wellknown corneal layers, Dua's layer is known for being surprisingly strong—as well as for emitting "a pretty loud popping sound" when it bursts, according to The Review of Optometry.