tunnel. So now let’s move on to the short
how they’re arranged alongside the extrinsic
tendons. So here we can see some deep dissections
of the hand. We can see that we’ve cut away
some of the tendons and we’ve opened up
the carpal tunnel. And here, we have removed some
of those tendons as well to look deep and
see some dorsal and palmar interossei muscles.
So if we have a look, we can see the all eight
tendons, see them here, flexor digitorum
profundus. And we can see the cut tendons here,
flexor digitorum superficialis, enters to the
central compartment of the hand by passing
through the carpal tunnel. And if we remember,
FDS, flexor digitorum superficialis, pass
to the middle phalanx of digits 2 to
5, whereas, FDP, flexor digitorum profundus,
pass to the distal phalanx of digits
2 to 5. So there’s an important arrangement
here that we need to observe. As the tendons
of flexor digitorum superficialis
pass to the middle phalanx, the tendons actually
split, and we can see that here. Here, we
can see the tendon of FDS passing towards
the middle phalanx and its tendons splitting.
You see it here. We can also see it happening
here. See the tendons splitting into two as
they go and attach to the middle phalanx.
We can see it again here once these tendons
are actually being reflected somewhat. See
the tendon of flexor digitorum superficialis
here. And we can see it actually splits,
one going down onto this lateral side and
one just going down this medial side. It’s
a little bit covered by this, the tendon of
flexor digitorum profundus. The tendon
of flexor digitorum profundus,
as we can see, passes deep through this split.
So as the tendon of flexor digitorum superficialis
split, so the deeper tendon of flexor digitorum
profundus passed through this split as it
passed the distal phalanx. And this is a really
important arrangement. We can see it again
here. Flexor digitorum profundus is passing
deep to flexor digitorum superficialis.
And then as it splits, the tendon here is splitting,
FDP passes deep to it. And this enables the
tendon of FDP to pass to the distal phalanx.
We also have some vincula tendinum. We have
two of these, and these are very small little
slips of tissue. And they actually attach
the tendons of FDP and FDS to each other and
also to the phalanx. We can see these small
little tendinous slips. We can see them passing
down here. And here, we have a longum and
a brevia. We have a long one and we have a
short one. And these are important in connecting
those two tendons to the tendinous sheaths,
and also in permitting some microcirculation.
So these carry some micro blood vessels to
the tendons for their blood supply.
So they’re really important in connecting the tendons
to each other and also to the phalanges and
also permitting some micro circulation so the
tendons can receive their oxygen and nutrients.
So if we now move on to the short muscles
of the hand, we can see that we have a whole
series of what’s known as lumbricals. We
have lumbricals going from fingers 2 and 3.
These are known as lumbricals 1 and 2. And
lumbricals going from fingers 4 and 5, and
these are known as 3 and 4. So we can see
these lumbricals here. We’ve got a lumbrical
here, we’ve got a lumbrical here, we’ve
got a lumbrical here, and we have a lumbrical
here. And these lumbricals are coming from
the lateral two tendons of flexor digitorum
brevis. And they’re coming from the medial
two tendons of flexor digitorum profundus.
So now let’s turn to a series of short muscles
known as your lumbricals. And we can see the lumbricals
here. We have four of them. And the lumbricals
are either unipennate or bipennate in arrangement.
They either have one kind of head or they
have two heads originating from different
places. And we can see we have a unipennate
lumbrical here. And this lumbrical is important.
It’s coming from the tendon of flexor digitorum
profundus. So, all of the lumbricals come
from the tendons of flexor digitorum profundus.
And as they run over towards the extensor
expansion, they are running over the metacarpal
phalangeal joints and then over the
interphalangeal joints. So these muscles are
capable of working across
two different joints. We have a lumbrical
here. We have another lumbrical here, our
two lateral unipennate lumbricals. And then
we have two bipennate lumbricals. We can see
we have one here and we have one here. So
we have four lumbricals together. Notice how
they all originate from the tendon of flexor
digitorum profundus, and they don’t work
on the thumb. They don’t work on the first
digits. They’re only associated with digits
2, 3, 4, and 5. So if we have a look,
we can see lumbricals
1 and 2. These are originating from the lateral
two tendons of FDP, and these are our unipennate
one as I indicated. And then we have lumbricals
3 and 4 and they’re originating from the
medial two tendons of FDP, and these are bipennate.
They insert onto the lateral surface of the
extensor expansions as I mentioned of the
digits 2 and 5. So they don’t work on the
thumb, just digits 2 to 5. The lumbricals
1 and 2, the lateral two lumbricals are innervated
via the median nerve, whereas the lumbricals
3 and 4 associated with the medial tendons
of FDP are innervated via the ulnar nerve.
So we can see the lumbricals have a different
innervation, a different nerve supply. The
function of these lumbricals is important
because they can both flex and extend different
joints, so they can flex the metacarpophalangeal
joint, the joint between the phalanges and
the metacarpals. So they can flex that joint,
the phalanges here and the metacarpals. They
can flex that joint. And they’re also capable
of extending the interphalangeal joints. So they’re
capable of flexing that joint but also extending
the interphalangeal joint. And that is because
of their position. They run anterior to the
metacarpophalangeal joint so they can
And by passing to the extensor expansion,
they’re running posterior to the interphalangeal
joint. So a contraction of these muscles allows
flexion of that joint, the metacarpophalangeal,
and extension of the interphalangeal joint.
This position here is important if you’re
holding a pencil if you’re about to write.
So these muscles are important for the digits
to assume complex positions. Now let’s
carry on looking at a series of
short muscles, and these are known as your
interossei muscles. We have two different
types of interossei muscles. We have dorsal
interossei positioned on the dorsal aspect
of the hand. And we have palmar interossei
muscles positioned on the palmar surface.
Here, we can see the dorsal interosseous muscles.
We have four of them. We can see one, two,
three, four. And we can see these have
two heads. They’re running from the adjacent
surfaces of all of the metacarpals. So we
can see the dorsal interosseous here is running
from the medial surface of the first metacarpal
and the lateral surface of the metacarpal
here of the second metacarpal. And we have
similar arrangements. And these are passing towards
the extensor expansion, those extensor hoods
over the digits.
And then we have the palmar interossei. These
are just running from one of the metacarpal
surfaces, and we can see they’re coming
from digits 2. They’re coming from digit
4, and coming from digit 5. Digit 3 does not
have an attachment of these interossei muscles.
The interossei muscles do not attach. So we
can see that these muscles are going to be
associated with abducting and adducting the
fingers. We can see the dorsal interossei
are coming from the dorsal sides of all the
metacarpals, these are bipennate muscles.
And the palmar interossei, as I said, comes from
the palmar sides of metacarpals 2, 4, and 5.
They insert onto the base of the proximal
phalanges and also the extensor expansions.
The nerve supply for these interossei is via
the ulnar nerve, the deep branch. And the
dorsal interossei are associated with abducting
digits 2 to 4, abducting digits 2 to 4. Palmar
interossei are associated with adducting digits
2, 4, and 5, this time towards the axial line.
I’ve put that here; towards the axial line
and away from the axial line. What does that
mean? Well, if you imagine the axial line
is running down in line with the middle finger,
so an axial line is running down here. This
is the line at which these fingers are going
to be abducted or adducted. And we can see
that with contraction of these muscles, we
can put the muscles in cartoon form here.
With this axial line, we can see that the
dorsal interossei are going to pull the fingers
away from this axial line.
So this dorsal interossei can pull that away.
This dorsal interossei can pull this middle
finger away. It can also, because we have
the dorsal interossei on the other side, abduct
it the other way. For the fingers, we don’t
talk about abduction and adduction as moving
them towards the midline of the body. We talk
about moving away from this axial line.
Therefore, the middle finger can both abduct this way,
and it can abduct that way, whereas the other
fingers will all abduct away from this axial
line like that. The middle finger can abduct
away either sides. If we look at the
palmar interossei, then
we look at adducting. So palmar interossei
are adducting and they’re going to draw
the fingers towards the middle finger, towards
the axial line. So we can see that this interossei
will move it across. This interossei will
move it across. This interossei will also
move it across. So we’ve got our middle
finger. We can adduct here, we can adduct
here, we can adduct here. So, all the
fingers are together. Don’t forget we have
adductor pollicis so we can move the
thumb across. It doesn’t need an
interosseous muscle. So here, we can see
the origins and insertions
of these muscles. The easy way to remember
the function is for the dorsal interossei
to use the D from dorsal and the AB, so you
can DAB, dorsal interossei abduct. And you
can have PAD, using the P from palmar interossei.
PAD as the palmar interosseis adduct.
So in this lecture, we’ve looked at the
dorsal aspects of the hand. We’ve looked
at the extrinsic extensor tendons and tendinous
sheath. We’ve looked at extensor expansions
and the anatomical snuff box, its boundaries
and contents. We then looked at the palmar
aspects. We looked at the carpal tunnel and
the ulnar canal, the boundaries and contents.
We then looked at compartments, central hypothenar,
thenar, adductor, and interosseous, and we
looked at the muscles within each of the compartments.
And then we looked at the extrinsic flexor tendons.