So there's more going on even beyond the forearm.
We have to deal with the hand and the wrist.
So when we look at the hand
and we're looking on the palmar side
or what we consider an anatomic position,
the anterior surface,
we see another wide flat sheet of connective tissue
which we said those things are called aponeurosis.
So this is an aponeurosis in the palm holding together
all these digits and all of their tendons,
and we call that the palmar aponeurosis and we can see
some of the tendons for those muscles we already mentioned.
For example, here are the tendons
for flexor digitorum superficialis.
So even though the muscle that acts
on these digits was way up in the forearm,
they have to have really long tendons
to get to the digits in order to act on them.
And so, for example, here we see them
ending on the middle phalanx
but we also had flexor digitorum profundus,
a deep layer of muscles that are going to cause flexion of the digits.
And they're going to go all the way
to the distal phalanx.
And so, that creates a bit of a traffic jam
so you'll notice the neat thing
that happens is the distal end
of the flexor digitorum superficialis,
those tendons will split to let the tendon of the flexor digitorum profundus
pass through on its way to the distal phalanx.
So before they get there, they're going to have to go through
the wrist and something called the carpal tunnel,
something you probably heard of before
because it has a lot of clinical significance.
So here, in cross section,
are all of those wrist bones or carpal bones
and there's a connective tissue sheet on the anterior
or palmar surface called the flexor retinaculum.
Retinacula are things that sort of keep tendons in place
and kind of provide a fulcrum for their action to take place.
And in the tunnel created by the flexor retinaculum
and the carpal bones is the carpal tunnel
and we see some important tendons going through here.
We have the flexor digitorum profundus
and flexor digitorum superficialis tendons
as well as the flexor pollicis longus going off to the thumb.
In addition to all of these tendons, we have our median nerve
and this is how you can get carpal tunnel syndrome
is with a lot of overuse of these tendons,
they can become inflamed and swollen
and there's not a lot of room in that tunnel
and they can compress the median nerve.
And that can cause symptoms distally to that point
meaning a lot of numbness and weakness
and what we call the thenar compartment
which is our other word for the base of the thumb.
Which brings us to that compartment.
So here, we have what are called thenar muscles
and they act on the thumb
so you'll see the word pollicis, opponens pollicis.
Opponens is a bit of a weird one.
Opponens is something called opposition.
It's basically a movement where if you're trying to bring
your thumb over to your little finger or digiti minimi,
that would be called opposition.
And we also have the abductor pollicis brevis.
We also have the flexor pollicis brevis.
So these thumb muscles are called the thenar muscles.
On the opposite side of the hand where we have our little finger,
we have the hypothenar muscles.
And here, we're going to have the opponens
digiti minimi doing the same motion
we just talked about with the thumb opposition
but for the little finger.
And we also have the abductor digiti minimi
and the flexor digiti minimi brevis.
It's a real fun one to say and because we said the compression
of the median nerve in that carpal tunnel
can cause thenar weakness, you can assume that,
well, that's what innervates these thenar muscles.
And over on the hypothenar side,
that's where we have ulnar innervation.
So now, we're going to look at some other very tiny muscles
that the ulnar nerve also innervates
and these are the palmar interossei.
They tell us a little bit about where they are
because palmar is going to refer
to the anterior surface of the hand
and what these muscles are going to do is adduction
but not quite the same adduction
that we're used to in other areas.
Here, we're talking about bringing closer to the middle finger.
So we have this unusual midline that exists
only in the hand where the midline of the hand is the middle finger.
So bringing these three fingers closer
to the middle finger is considered adduction
and the mnemonic that I'm about to point out
starts with PAD, so the palmar interossei adduct.
So, P-A-D is how you remember that.
If we go to the opposite side,
we have the dorsal interossei and dorsal is another term
for posterior so we're talking about back of the hand.
And these will have the opposite movement.
These are going to be abduction,
moving away from the midline created by the middle finger
but it creates an unusual situation
where since the middle finger is the midline,
movement in either direction will be abduction.
In this sense, the middle finger can only abduct.
And to finish off the mnemonic DAB, so DAB, PAD,
so dorsals abduct and palmars adduct.