... but it also flares into the palm, or this palmar aponeurosis — which I'm going
to zoom in for you — that you can see in the palmar surface of the hand here.
Some of you are losing muscles!
And I'm not talking about because you're sitting on your Gluteus Maximus all day long,
watching amazing anatomy videos on YouTube.
I'm talking about that you were never even born with them!
There are a handful of muscles in the human body that are variable from person to person
because these are thought to be evolving out of humans.
We need to talk about why that is,
and we're gonna even talk about a little test you can do to see if you've got one in your forearm.
And don't worry — if you don't have this muscle,
you can just tell your friends that do that you're a little bit more evolved than them.
So let's do this!
As I already mentioned, there are a handful of muscles in the human
body that are variable from person to person.
And we're going to focus on this one in the forearm because you can actually figure out if
you have this just sitting here watching this video with a little test that we'll show you.
The other ones, you're gonna have to do some sort of imaging study to find out
if you have those, and that's just not really feasible for most of us.
But to understand how this works with this forearm, let's take a look at the
upper limb dissection to get some context around the muscles of the upper limb.
So here is a dissection of the upper limb.
Just FYI you guys — people get a little bit uncomfortable with fingertips and the
skin of the fingertips, so we've just covered that
for your viewing pleasure — or your viewing comfort, I guess I should say.
But let me move the upper limb so you can orient yourselves.
It's essentially just like my upper limb is sitting like so.
Now this is the brachium, or the upper arm,
which there are 4 total muscles here in the brachium, or the upper arm.
Now if I move down here and grab the forearm — which the fancy-pants name for forearm in
anatomy is the antebrachium — there are 20 muscles here.
So 4-20.
Some of you remember 420 for certain extracurricular activities.
I remember 420 because of its reference to anatomical awesomeness.
So regardless of how you want to remember the reference of 420,
let's just go a little bit further.
So again, 4 muscles here, 20 muscles here.
But there are 11 more inside the hand.
And if we take a step back and kind of think of that logic — the muscles of the brachium,
or the upper arm, are going to mobilize the elbow.
And what does the elbow do?
We're like flexion, extension, and we're kind of done with also some supination, and that's it.
But when we get to the forearm muscles and the hand muscles,
we're doing all sorts of things like, you know, abduction and adduction.
Waving, things like this... wiggling those fingers... doing "the Spock"...
you know, opposition — things of that nature.
Lots of specialized work here.
So again, it would make sense to have more muscles
for more, you know, fine motor movements that we're going to do with the wrist and the hand.
Now 20 muscles here, right?
Some of you only have 19....
And finally, we can talk about this mystery variable muscle here.
So let's take a look here at the cadaver again, and here is
this mystery muscle, called the Palmaris Longus.
Now you can see why I got the name Longus, because it's a fairly long tendon here.
There is a Palmaris Brevis, FYI.
But it also flares into the palm, or this Palmar Aponeurosis — which I'm going to
zoom in for you — that you can see in the palmar surface of the hand here.
Now again, this muscle coming all the way back to the elbow is not a very big
muscle here — just a small little muscle belly, so not a very powerful muscle.
But what does it do?
This Palmaris Longus muscle can weakly help flex the wrist.
I say weakly, because there are other muscles that are much more powerful
and stronger with flexing the wrist.
Now because it goes to the palm of the hand and that Palmar Aponeurosis, when you do certain
gripping motions it can put tension on the skin and the connective tissues of the palm to kind
of help create that cup in the palm of your hand that you're seeing here with gripping.
So this always comes back to this question of,
"why do some people have this muscle and others not have the muscle?"
And those who don't have these variable muscles that we've mentioned, don't really miss them.
And what I mean by that is that they're not necessary
for day to day functions or physical activities.
For this muscle in particular — remember we had 11 other muscles in the hand
and all these other forearm muscles that could perform similar functions.
So if you don't have this muscle, you can still do all the hand and wrist
movements that you would need to do even without the small little Palmaris Longus.
And of course, this knocks on the door of evolution.
And to give this brief overview — or this idea of how this works — is animals,
over the "bazillions" of years of development and evolution and things of that nature,
they were exposed to certain environmental factors and participated in certain activities,
and a combination of all these variables activated and turned on certain genes.
And as those genes were more active and more frequently turned on and expressed,
those genes were more likely to be passed on to offspring in generations.
And as things got more specialized,
some muscles took over other functions and rendered other muscles less useful.
And that's the idea of this muscle
kind of evolving out of humans, as well as the other muscles.
And just one quick little thing I need to mention before I show you the test to see if you have this
muscle — Justin and I have been posting on TikTok, Instagram and YouTube for a little while now,
and we've noticed there are some trigger words or trigger topics
that get people really fired up in the comments section.
Evolution tends to be one of those, you know?
So whether you believe in evolution, or have some religious convictions,
or a combination of the two — go ahead and discuss, but just be nice to each other.
It's not that hard!
It's — you know, the Institute of Human Anatomy comment section is a safe space, okay?
And I'll even start — I believe in evolution — obviously, because I'm teaching about this.
I think the evidence is pretty strong.
However, I grew up in a strongly religious family, and i don't necessarily think they
have to go against each other — they can coexist, in my opinion.
Let me know what you think below.
So finally, we get to test if you've got this muscle or not.
To do this, I must de-glove.
Okay!
So what you're going to do, is you're going to slightly flex your wrist.
You don't want to crank this thing all the way up.
You just want to slightly give it some flexion,
and that's not going to give you everything you need.
What you need to do, is slightly flex the wrist,
and then pinch your pinky and your thumb together pretty tightly.
And you can see that difference of that tendon that starts to bulge out of my skin there.
Now don't get confused by the secondary tendon that's next door to it,
as you can see there's two tendons here, but it's the one that's bulging out more.
The one that's closer to the thumb
is actually this other muscle right here called the Flexor Carpi Radialis.
If you want to get more information on that, Justin just did a
Carpal Tunnel video on it, so fun there.
But again, take a look at how that works.
But I need to show you — my other side.
So if you take a look here, I do not have it on my left wrist or left forearm — it's missing there.
I just have that other tendon, that Flexor Carpi Radialis tendon,
but I'm missing the Palmaris Longus.
And a lot of you will see that you'll have it on one side versus the other...
you may have it on both sides... or you may not have it at all!
And again, like I mentioned at the beginning of the video,
if somebody tries to make fun of you for not having a Palmaris Longus,
your rebuttal is that you are a little bit more highly evolved than them.
My left side's a little confused compared to my right side — it wanted to evolve
faster than my right side, I guess... who knows?
And one cool thing, from a clinical perspective.
For those who have this tendon you could use it
for a graft if you had some injury to a certain ligament.
For example, pitchers will sometimes injure — pitchers like baseball pitchers — will sometimes
injure this ligament called the Ulnar Collateral Ligament.
And to help repair this ligament, you could take this tendon from the Palmaris Longus
and use it as a graft to repair this damaged ligament.
So this wimpy little muscle can be used for, you know, showing people cool tricks.
But at the end of the day — eh...
As always, thanks for watching and going on this tour of the
upper limb and the Palmaris Longus with us.
Please like, subscribe, ring the bell so you know when we drop new videos.
We love the comments everybody — please blow that section up.
We have our affiliates down below — we love and appreciate all of your support.
And have fun testing your Palmaris Longus with your friends and family.
I don't know what that was... like spirit fingers... it has
nothing to do with Palmaris Longus... okay bye!