Description

Carpal Bones (Ossa carpi)
The wrist consists of 8 carpal bones arranged in two rows: a proximal row and a distal row. These short, irregular bones allow for the wrist’s flexibility and stability.

Proximal row (lateral to medial):

Scaphoid (os scaphoideum) – Articulates proximally with the radius and distally with the trapezium and trapezoid. Medially connects with the lunate. Notable for its tubercle on the palmar side, contributing to the carpal tunnel’s lateral wall.
Lunate (os lunatum) – Lies between the scaphoid and triquetrum. Articulates proximally with the radius and distally with the capitate.
Triquetrum (os triquetrum) – Medial to the lunate. Articulates with lunate, pisiform (anteriorly), and hamate.
Pisiform (os pisiforme) – A sesamoid bone embedded in the tendon of flexor carpi ulnaris. Articulates with the triquetrum. Serves as the attachment for:
Pisohamate ligament
Pisometacarpal ligament
Origin for abductor digiti minimi

Distal row (lateral to medial):

Trapezium (os trapezium) – Articulates with the 1st and 2nd metacarpals. Located beneath the thumb. Features:
Tubercle of trapezium
Groove for the tendon of flexor carpi radialis
Trapezoid (os trapezoideum) – Medial to the trapezium. Articulates with 2nd metacarpal, scaphoid, and capitate.
Capitate (os capitatum) – The largest carpal bone, articulates with 3rd metacarpal, lunate, scaphoid, trapezoid, and hamate.
Features: Head (proximal) and base (distal)
Hamate (os hamatum) – Medial-most bone in the distal row.
Articulates with 4th and 5th metacarpals, capitate, and triquetrum.
Features the hook of hamate, serving as an attachment for:
Pisohamate ligament
Flexor digiti minimi
Opponens digiti minimi

Mnemonic used:
“Scary Lions Try Pizza, Then They Chase Hamsters”
(Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate)

Metacarpal Bones (Ossa metacarpi)

There are 5 metacarpals, numbered I–V (lateral to medial), forming the palm of the hand.

Each consists of a base, shaft, and head.
The 1st metacarpal is shorter and thicker with a saddle-shaped base that articulates with the trapezium, allowing thumb opposition.
The heads articulate with the proximal phalanges, forming the metacarpophalangeal (MCP) joints, visible as knuckles during flexion.

Phalanges (Ossa digitorum)

The hand contains 14 phalanges divided into:

Proximal phalanges (phalanges proximales) – Present in all 5 digits.
Middle phalanges (phalanges mediae) – Absent in the thumb.
Distal phalanges (phalanges distales) – Present in all 5 digits.

Structural components:

Each phalanx has a base, shaft, and head (except distal phalanges).
Distal phalanges end in a tuberosity of the distal phalanx (tuberositas phalangis distalis) that anchors the flexor digitorum profundus tendon and supports the fingertip pulp.

Sesamoid Bones (Ossa sesamoidea)

Found typically at the 1st MCP joint embedded in the tendon of flexor pollicis brevis.
Function as biomechanical levers that enhance thumb flexion force.
Can also appear at the 2nd, 3rd, or 5th MCP joints, depending on population.

Radiological study mentioned:

Journal of Orthopaedics, Trauma and Rehabilitation (2017) analyzed over 300 Chinese hand X-rays.
Found sesamoid bones at the thumb MCP joint in 100% of cases.
Noted ethnic variation in occurrence at other MCP joints.
Left–right symmetry in sesamoid distribution was observed across all patients.

Clinical Relevance

Scaphoid fracture – Most common carpal fracture; risk of avascular necrosis due to poor blood supply.
Hook of hamate fracture – Common in sports with racquets or bats.
First carpometacarpal arthritis – Affects thumb base; impacts opposition.
Sesamoiditis – Inflammation of sesamoid bones, often misdiagnosed.
Fractures of phalanges/metacarpals – Common due to direct trauma or punching injuries.
Thumb opposition impairment – Due to dysfunction of saddle joint or thenar muscles.

PDF version of this lecture, quiz, and all my anatomy lectures in a structured order available on visit my website.

Sources:

Kozlowski, T. (2017). Memorix Anatomy, 2nd ed.

• Standring, S. (2020). Gray’s Anatomy, 42nd ed.
• Tubbs RS, Shoja MM, Loukas M. (2016). Bergman’s Encyclopedia of Human Anatomic Variation
• White TD, Folkens PA. (2005). The Human Bone Manual

Programs used: Complete Anatomy, Biorender, PowerPoint

Transcript

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This is your hand. Well… the bones of it.

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Beneath every movement are 27 bones that are
arranged in a precise, functional structure.

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8 of them form the Wrist,
and 19 of them form the hand.

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So what we are going to do in this video is to
go through all the bones that make up the wrist,

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and then we’re going to look at the bones of the
hand, basically the metacarpals and the phalanges.

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What’s up everyone, my name is Taim. I’m a
medical doctor, and I make animated medical

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lectures to make different topics in medicine
visually easier to understand. If you’d like a

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PDF version or a quiz of this presentation, you
can find it on my website, along with organized

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video lectures to help with your studies.
Alright, let’s get started.

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The bones of the wrist,
also known as, Carpal Bones.

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The carpal bones are really interesting; they are
small, irregularly shaped bones that give your

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wrist its ability to bend the way it does.
And they are arranged in two rows,

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a proximal row and a distal row.
Let’s do the proximal row first.

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The proximal row is basically the base of your
wrist as you see here. And just for orientation,

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here’s the radius on the lateral
side, and here’s the ulna medially.

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Now let’s take a closer look
at the four bones in this row.

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First up we have the scaphoid bone. This is
the most lateral of the proximal row bones,

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and it sits just underneath the radius.
Let’s look at it in a bit more detail.

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It has a proximal surface that articulates
directly with the radius. It has a distal surface,

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that connects with the trapezium. And it has
a medial surface, which is this shallow area

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that connects with the lunate. Another thing we
can see on this bone is that on the palmar side,

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it has a raised tubercle, called the tubercle
of the scaphoid. It contributes to forming the

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lateral wall of the carpal tunnel.
Alright, next to the scaphoid,

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we’ve got the lunate bone.
The lunate bone connects proximally

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with the radius alongside the scaphoid.
Distally it articulates with the capitate,

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the largest of the carpal bones.
There’s also a separate articular area

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distally that connects with the scaphoid.
And medially, there’s a flat surface

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towards the triquetrum.
Alright, the triquetrum is

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our next bone here on the proximal row.
If we zoom into it, you can see it has

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this surface here for the pisiform,
which sits nearly in front of it.

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There’s also a distal surface that connects with
the hamate, and another flat surface here that

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articulates with the lunate.
And finally, we’ve got the

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pisiform. This one’s so interesting.
It’s a small, pea-shaped sesamoid bone

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that sits on top of the triquetrum. It articulates
with the triquetrum through this single surface.

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And it serves as an anchor as well. The pisiform
is where the flexor carpi ulnaris tendon inserts.

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It also serves as the origin point
for the abductor digiti minimi.

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In addition to this, there are two ligaments that
attach here as well, it’s the pisohamate ligament,

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and the pisometacarpal ligament. Ligaments
and joints will be covered in the next video.

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But that was the 4 bones of the proximal row,
scaphoid, lunate, triquetrum, and pisiform.

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Now, let’s cover the distal row.
These are the four small bones that form

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the bridge between the wrist and the metacarpals.
And the first one is here called the trapezium.

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The trapezium sits just
beneath the base of the thumb.

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On its distal surface, this area here,
it articulates with the first metacarpal.

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There’s also this smaller facet that
connects with the second metacarpal.

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And on its medioproximal side, it touches
both the scaphoid and the trapezoid.

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And just like the scaphoid, it has a small bony
bump on the palmar side called the tubercle of

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the trapezium, which also contributes to
the lateral wall of the carpal tunnel.

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Another thing is, here you see the flexor
carpi radialis muscle with its tendon,

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you can actually see it runs through a shallow
groove on the trapezium called the groove for

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the tendon of flexor carpi radialis.
Next we have the trapezoid.

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It’s a small bone just medial to the trapezium.
Here is the proximal surface,

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this part connects with the scaphoid.
Then we’ve got its distal surface,

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which articulates with the second metacarpal.
On the medial side, it touches the capitate.

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And on the lateral side, it
connects back to the trapezium.

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Next we have the capitate.
This is the largest carpal bone,

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sitting in the middle of the wrist, right
behind your middle finger metacarpal.

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Let’s zoom in. This proximal surface here
connects with both the scaphoid and lunate.

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Then at the base, it connects
distally with the third metacarpal.

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On the medial side it touches the hamate, and
laterally, it connects with the trapezoid.

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You can also divide the capitate into two parts,
the head, which is the rounded proximal portion,

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and the base, which faces the hand.
And finally, we have the hamate.

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Hamate is at the ulnar side of the distal row.
This part of the bone, its medioproximal surface,

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connects with the triquetrum.
Then here, distally,

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it connects with the fourth and fifth metacarpals.
And laterally, it articulates with the capitate.

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But the most distinctive part of the
hamate is this, the hook of the hamate.

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It projects anteriorly, and it serves as
an important attachment site for things

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like the pisohamate ligament, and it’s also the
origin point for both the flexor digiti minimi

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and the opponens digiti minimi muscles.
So that was the distal row, trapezium,

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trapezoid, capitate, and hamate.
And together with the proximal row,

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that completes all eight carpal bones.
Now, to help you remember them,

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here’s a weird mnemonic:
“Scary Lions Try Pizza,

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Then They Chase Hamsters.”
Yeah, it’s weird.

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But that’s the point, the weirder it is, the more
likely you are to remember it. So now, anytime you

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think of wrist bones, you’ll probably picture
lions, pizza, and hamsters. You’re welcome.

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That was the carpal bones.
Now let’s do the bones of

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the hand. The bones of the hand consist of two
main groups, the metacarpals and the phalanges.

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To make this easier to visualize, let’s put the
bones back into the hand. As you can see here,

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the metacarpals form the middle part
of the hand, basically the palm,

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and the phalanges make up the fingers.
Let’s start with the metacarpals. There

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are five metacarpal bones, and they’re numbered
from lateral to medial, so thumb is number one,

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ending with the little finger as number five.
All five share the same general structure,

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they each have a base, a head, and a shaft. The
base is the proximal end that articulates with

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the carpal bones, and the head is the rounded
distal part that connects with the proximal

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phalanx of each finger. That’s also the part that
forms the visible knuckles when you make a fist.

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Now while they all follow this same structure,
each metacarpal has its own unique features. The

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first metacarpal, which belongs to the thumb,
is shorter and thicker than the others. Its

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base has a saddle-shaped articular surface for
the trapezium, which allows the thumb to oppose

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and rotate, which is a function that separates
human hand dexterity from most other species.

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Now let’s cover the fingers, the phalanges.
Each digit is made up of phalanges, and they’re

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categorized into three parts, proximal, middle,
and distal. The exception is the thumb, which

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only has two, a proximal and a distal phalanx.
The proximal phalanges are the first ones and all

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five digits have one. The middle phalanges are 1,
2, 3 and 4. Only the second through fifth fingers

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have these, the thumb doesn’t have middle phalanx.
The distal phalanges are present on all fingers,

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including the thumb. And so this is how they
all look like, they’re pretty straight forward.

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Now this is anatomy so let’s cover the
basic structures of them. Structurally,

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the proximal phalanges have a base at the proximal
end, a shaft in the middle, and a head distally,

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just like the metacarpals. The middle phalanx also
have a head, shaft and distal part. The distal

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phalanges have a base and shaft, however, instead
of a rounded head, they end in a flattened,

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widened area called the tuberosity of the
distal phalanx. This is the part that anchors

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the fingertip pulp and serves as the insertion
point for the flexor digitorum profundus tendon.

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So that was everything for the
bones of the hand.Just before

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we end this video. Do you know what those are?
These are called the sesamoid bones of the hand.

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These little bones are embedded within tendons,
often at points of high friction or pressure.

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And what they do is they act as something called
biomechanical levers, improving the mechanical

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advantage of the muscles that flex the thumb.
Although we always expect them at the thumb,

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sesamoid bones can also show up in other fingers,
but that varies depending on the population.

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Let me show you something interesting. This X-ray
here is from a study published in the Journal

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of Orthopaedics, Trauma and Rehabilitation
in 2017. The study looked at over 300 hand

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radiographs of Chinese patients and analyzed
where sesamoid bones were found in the hand.

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They found that sesamoid bones were present at
the thumb in 100% of cases. That’s expected. But

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notice how they’re just sometimes present on
the other joints in the hand indicating that

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the presence of these is very different between
the population. What’s even more interesting is

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that the distribution of sesamoid bones was
exactly the same in both hands in every case.

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The study found that these patterns aren’t
universal. Different ethnic populations have

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different prevalence rates. For example, compared
to European or Middle Eastern populations,

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Chinese individuals were more likely to have
sesamoid bones at the second and third MCP joints.

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So why does this matter clinically? Well,
these bones can sometimes cause problems,

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like inflammation, known as sesamoiditis,
fractures, or even mimic foreign bodies

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or fractures on X-ray. So recognizing
their typical locations can help avoid

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misdiagnoses. So next time you see a hand
X-ray, keep an eye out for these little bones,

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they might be more important than they look.
And with that, we’ve covered all the bones of

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the hand. In the next video, we will be covering
all the joints and ligaments of the hand. Click

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the next video and I’ll see you there.
If you want a handmade PDF version of this

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lecture, take a quiz to test your knowledge,
or access an organized list of all my videos,

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you can find everything on my website.
Thanks for watching! See you in the next one.