So I've just rotated the model around, so we're now looking at a plantar view, so we're
looking at the inferior surface of the foot. So I'll just remove away the plantar aponeurosis,
and we'll take a look at some of the muscles in the plantar group of muscles. So in the
plantar group you've got four different layers. So you've got this first layer, which is the
most superficial layer, and three other layers, which I'll come on to talk about. So these
muscles form a lot of the soft tissue bulk which you can feel in the foot. So I'll start
with this central muscle. So there's three muscles in this first group. So you've got
the flexor digitorum brevis muscle, you've got the abductor hallucis, and the abductor
digiti minimi. So right in the middle here, we've got the flexor digitorum brevis muscle.
So this originates on the calcaneus, on the medial process of the calcaneus, and it forms
four tendons which insert onto the middle phalanx of the lateral four digits. So it
inserts on the sides of the middle phalanges of the lateral four digits. So just like in
the hand, you've got the flexor digitorum superficialis and the flexor digitorum profundus
muscle. So in the hand, the flexor digitorum superficialis splits and it inserts on the
middle phalanges, and it allows the deeper tendon - the flexor digitorum profundus to
pass through - so it's exactly the same in the foot. So the flexor digitorum brevis muscle,
which is this muscle here, is analogous to the flexor digitorum superficialis, so it,
because it's the superficial muscle, and then it splits and inserts on the sides of the
medial, the middle phalanx to allow the deeper tendon - so the flexor digitorum longus muscle
- to pass through. So the flexor digitorum longus is analogous to the flexor digitorum
profundus, because it's the deep tendon. So what this muscle does is that it flexes the
lateral four digits at the proximal interphalangeal joint. So this muscle is innervated by the
medial plantar nerve. So just lateral, sorry medial to this muscle, we've got this muscle.
This is the abductor hallucis, so you can feel this in your foot, it makes up a lot
of the bulk that you can feel in the medial side of your foot. So this originates on the
medial process of the calcaneal tuberosity and it inserts at the base, it inserts medially
on, at the base of the proximal phalanx of the great toe. So this muscle can flex the
great toe at the MTP joint, and it also obviously abducts at the MTP joint - as the name suggests.
So the third muscle of the first layer is this muscle here, the abduct digiti minimi,
so this muscle sits laterally and it abducts the little toe at the MTP joint, so this has
got an origin on the lateral side of the calcaneal tuberosity, and it also stretches across to
the medial process, so it originates on the medial and the lateral process, of the calcaneal
tuberosity, so it's got quite a large origin. And then it runs forward and it inserts at
the base of the proximal phalanx laterally, so it abducts the little toe at the MTP joint,
so it brings the little toe away from the midline. So the abduct digiti minimi muscle
is innervated by the lateral plantar nerve, and the abductor hallucis is innervated by
the medial plantar nerve. So those are the three muscles of the first layer. So a just
quick note about abduction and adduction in the foot. So in the foot abduction and adduction
are defined in relation to a longitudinal axis that runs through the second digit, so
abduction is movement, any movement away from this axis, and adduction is any movement towards
this axis. This is the same as in the hand, so abduction and adduction are defined relative
to a midline that runs through the middle digit, so abduction is movement away from
this line, and adduction is movement towards this line. So it's just to clear up any confusion
that might arise because when we talk about abduction and adduction in the rest of the
body we talk about it in relation to a central midline that runs through the centre of the
body, so abduction is movement away from this central midline and adduction is movement
towards this. So in the foot and hand, the foot and hand have their own midlines. So
next we've got the second layer of muscle, so I'll just remove this superficial layer,
and we'll take a look at those. So immediately deep to the first layer, you've got the flexor
digitorum longus tendon. So this is the tendon which passes through the flexor digitorum
brevis and it inserts distally on the lateral four phalanges. So the muscles of the second
layer are related to this tendon, because they lie at the same level as this tendon.
So we've only got two muscles in this layer, it's quite an easy layer. So in layer two
we've got two muscles, in layer three we've got three muscles. So in this second layer
we've got the quadratus plantae, and we've got the lumbricals. So the quadratus plantae
muscle is this muscle here, which lies posteriorly. So it's got these two heads as you can see,
it's got a medial and a lateral head. So the lateral head originates on the lateral process
of the calcaneus...calcaneal tuberosity, and the medial head originates medially on the
calcaneus. So this, these two heads form this tendon which inserts onto the lateral side
of the flexor digitorum longus tendon. So you can see it attaching to the tendon here.
So because of its attachment on this tendon, it actually just helps this tendon to flex
the lateral toes, so toes two to five. So this muscle is actually innervated by the
lateral plantar nerve. So that's the quadratus plantae muscle. So next we've got the lumbrical
muscles, so we've got four lumbricals. So just like in the hand, the lumbrical muscles
originate from the sides of this tendon, so this is the flexor digitorum longus, and in
the hand, they originate from the sides of the flexor digitorum profundus muscle. So
just like I mentioned before, the profundus muscle is analogous to the flexor digitorum
longus muscle. So we've got these four lumbricals. So the first lumbrical originates from the
medial side of this tendon to the second toe, so the, so this only has one origin, whereas
the other three originate from the adjacent sides. So these are bipennate muscles, so
they have two, two sort of, they have two sets of fibres which converge onto this central
tendon - so they originate on the adjacent sides of the flexor digitorum longus tendons,
and they then insert onto the extensor hood of these lateral four digits. So because of
their insertion onto the extensor expansions, they actually can flex the MTP joints, while
extending the interphalangeal joints. So the lumbrical muscles are innervated by the medial
and lateral plantar nerves, so the first lumbrical is innervated by the medial plantar nerve
and the other three lumbricals are innervated by the lateral plantar nerve. So that kind
of makes sense. So those are the two muscles you have in the second layer. So remember
second layer - two muscles; third layer - three muscles, so I'll come on to talk about the
next layer now. So I'll just remove away the second layer and we'll take a look at the
third layer. So the three muscles you have in the third layer are associated with the
little toe and the big toe. So with the little toe you've got the flexor digiti minimi brevis,
and related to the big toe, you've got the adductor hallucis, and you've got the flexor
hallucis brevis. So first we'll just take a look at this medial muscle, so the flexor
hallucis brevis muscle. So you can see it here lying underneath this tendon. So this
tendon runs inferiorly to this muscle, and it's the tendon of the flexor hallucis longus
muscle. So the flexor hallucis brevis muscle is quite interesting because it's got two
origins and two sort of heads where it inserts. So you can see one origin on this bone, so
this is the lateral, one of the lateral tarsal bones, so it's the cuboid bone. And this tendon
here is the tendon of the tibialis posterior muscle. So the medial side of the flexor hallucis
brevis muscle actually originates on the tendon of the tibialis posterior muscle, and laterally
you've got this origin on the cuboid bone. So then anteriorly where the, or distally
where this muscle inserts, it actually has two heads, so this is shown a little bit short
of where it actually inserts, because this is still the end of the metatarsal, so the
head of the metatarsal, and this muscle actually inserts medially and laterally on the base
of the proximal phalanx of the great toe. So it's shown with its two heads here, so
splitting medially and laterally, but it actually inserts a bit further up on the base of the
proximal phalanx of the great toe. So this muscle is innervated by the medial plantar
nerve and its function is to flex the big toe at the MTP joint. So next we've got the
adductor hallucis muscle, so we've got this in the hand as well, so it's exactly the same
- it's got a transverse head and an oblique head. So the transverse head runs horizontally
across the foot, and it originates on the deep transverse metatarsal ligament, so you
can see this ligament here, running across the MTP joint, so it originates on the deep
transverse metatarsal ligament and the plantar ligaments of these lateral three toes, and
then it inserts on the base of the proximal phalanx. So again, for some reason it's shown
a little bit out of place here, it's shown inserting on the metatarsal, whereas it obviously
inserts at the base of the proximal phalanx, so a bit further up here. And then you've
got the oblique head, so it's called the oblique head because the fibres are angled obliquely,
so this muscle originates on the bases of metatarsals two to four, so these, metatarsals
two three and four, and it also has an origin on this tendon here. So if you remember from
my other tutorials this tendon is the tendon of the peroneus longus, or the fibularis longus,
so it enters the foot laterally and crosses over underneath the cuboid bone to insert
medially on the foot. So the oblique head of the adductor hallucis muscle originates
on the tendon, this tendon and also on the bases of metatarsals two to four, and it inserts
at the base of the proximal phalanx of the great toe. So as the name suggests, this muscle
adducts the great toe at the MTP joint and both these muscles are innervated by the lateral
plantar nerve. So finally we've got this muscle here, this little muscle the flexor digiti
minimi brevis. So this just actually means the flexor of the...the small flexor of the
smallest toe. So as you can see it originates on the base of the fifth metatarsal, and it
inserts laterally on the base of the proximal phalanx of the little toe. So it flexes the
little toe, and this is innervated by the lateral plantar nerve. So this muscle also
originates, like the oblique head of the adductor hallucis, this muscle actually also has an
origin on the tibialis, sorry the fibularis longus tendon, so this tendon is shown slightly
proximal to where it should be. So you've got this groove here on the cuboid bone, so
this tendon actually runs more like this, in this plane. So this flexor digiti minimi
brevis muscle also originates on the peroneus, or fibularis longus tendon. So those are the
three muscles of the third layer of the plantar group. So hopefully you're seeing some similarities
to the muscles of the hands now, so remember my analogy to the flexor digitorum superficialis
and profundus with the flexor digitorum brevis and flexor digitorum longus. And some of the
muscles I've talked about just now are similar to the muscles of the thenar and hypothenar
eminence in the hand, but you don't have an opponens muscle, so you've got the flexors
and the abductors of the great toe, but there's no opponens muscle in the foot. And you've
also got adductor of the great toe, which is similar to the muscles of the hand, and
you've got lumbricals which are similar because they originate on the tendon of the flexor
digitorum longus muscle, which is analogous to the flexor digitorum profundus muscle.
So by looking at these kinds of similarities, it makes learning about these muscles a little
bit easier. So I'll just remove these muscles of the third layer and we can look at the
fourth and final layer, and this is an easy layer because it just includes the interosseus
muscle, so you've got the plantar and dorsal interosseus muscles. So just like in the hand,
the function of the interossei muscles can be remembered with the mnemonic "PAD" and
"DAB". So Plantar ADduct - A D duct, and Dorsal abduct. So I've just isolated the interossei
muscles, and you've got plantar and dorsal interossei muscles, so the plantar interossei
muscles lie inferior to the dorsal interossei muscles, so you've got three plantar interossei
muscles, so there's an additional one shown here which doesn't exist. So you've got three
interossei muscles, which originate on one side of metatarsals three to five, so this
is three four and five, and they originate medially on the sides of these metatarsals.
So these plantar interossei muscles are unipennate, so they only originate on one side of the
metatarsals. And then they insert at the base of the proximal phalanges of digits three
to five and also on the extensor expansions of these digits. So you can see because of
their insertion medially, they will adduct these three, these three digits so they'll
bring it closer towards the midline of the foot. So the plantar interossei muscles are
innervated by the lateral plantar nerve. So I'll just get rid of the plantar interossei
muscles and we can see the final set of muscles - the dorsal interossei muscles. So there
are four dorsal interossei muscles and these are a little bit different because they are
bipennate muscles, so they originate on both sides of the metatarsals. So you can see here
you've got dorsal interosseus muscle two three and four attaching laterally on the bases
of proximal phalanges two to, two to four. So this will cause the, these bones to be
abducted at the MTP joint. And then you've got this fourth one - so you don't have four
plantar interossei muscles, so this first dorsal interosseus muscle inserts medially.
So the second toe can be abducted either side. So the dorsal interosseus muscles abduct the
digits two to four and they're innervated by the lateral plantar nerve, but you've also
got the first two dorsal interosseus muscles receiving innervation from the deep fibular
nerve. So those are the, those are the muscles, the intrinsic muscles of the foot, there's
quite a lot to learn there, but the anatomy is quite similar in some respects to the anatomy
of the hand, and a lot of anatomy is logically named and if you think about it logically
it becomes easier to remember. So I hope that has made things a bit easier for you to learn.