MUSCLES OF THE LEG AND FOOT.
General arrangement of the muscles with regard to the
skeleton.--Anterior muscles of the leg (_tibialis anticus_ and
_extensors_).--External or _peroneal_ muscles; relations of the
peroneus longus with the sole of the foot; its influence on the
form of the foot.--Posterior muscles; _gastrocnemius_ (details
of its composition and form). _Soleus_ muscle, _plantaris_,
_tendo Achillis_.--Muscles of the foot; 1st, dorsum of foot
(_extensor brevis_ muscle); 2nd, muscles of the sole of the foot.
_Muscles of the leg._--The arrangement of the skeleton of the leg
(tibia and fibula) is such that we might expect _a priori_ to find
four muscular masses, one on each of the surfaces of the skeleton,
but as the internal surface of the tibia is subcutaneous (2, Fig.
84), is not covered by any muscle, and is overlapped by the anterior
and posterior fleshy masses, it forms a long flat surface, slightly
hollowed, extending from the inner side of the knee to the internal
malleolus. The leg, therefore, presents for our study only three groups
of muscles, occupying respectively the anterior or antero-external, the
external or peroneal, and the posterior regions of the limb.
I. _Anterior muscles_ (Fig. 84).--Arranged in the space which separates
the fibula from the tibia, the muscles on the front of the leg are
three in number, called, from within outwards, the _tibialis anticus_,
the _extensor proprius hallucis_, and the _extensor longus digitorum_.
The _tibialis anticus_ (3, Fig. 84) arises from the external surface
of the tibia, and from the deep fascia over it (page 146), and
descends obliquely downwards and inwards in the form of a prismatic
or fusiform fleshy mass, of which the lower end gradually narrows, to
be replaced by a strong tendon in the lower third of the leg. This
tendon, inclining more and more to the inner side (2, Fig. 86), passes
obliquely over the anterior surface of the lower end of the tibia, in
front of the internal malleolus. It glides beneath the anterior annular
ligament of the ankle, and reaches the inner part of the dorsum of the
foot (3, Fig. 86), where it is inserted into the internal cuneiform,
and the base of the first metatarsal bone. It flexes the foot on the
leg, and inverts it, since it draws the dorsal surface of the foot
towards the anterior surface of the leg, while at the same time it
turns the foot inwards, and slightly raises its inner border. This
muscle, during contraction, shows externally all the details of its
shape--in the leg a fleshy mass which slightly overlaps the anterior
border of the tibia or shin, and in front of the ankle an oblique cord
marking clearly the direction of the tendon.
The _extensor proprius hallucis_ (5, Fig. 84) is concealed at its
origin between the tibialis anticus and the extensor longus digitorum.
Only its tendon appears superficially (2, Fig. 85) in the lower third
of the front of the leg, on the outer side of the tendon of the
tibialis anticus. It passes beneath the annular ligament of the ankle
and along the inner part of the dorsal surface of the foot (4, Fig.
86), to be inserted into the base of the terminal phalanx of the great
toe. When the great toe is forcibly turned up during extension this
tendon is clearly shown throughout its entire course. In a normal foot
this tendon occupies a straight line from the middle of the ankle-joint
to the great toe, and the inner border of the foot and great toe should
be parallel to it. In other words, the great toe should be in a line
with the inner border of the foot (Fig. 52, page 151).
[Illustration: FIG. 84.
MUSCLES OF THE ANTERIOR REGION OF THE LEG.--1, tendon of the
rectus femoris;--2, tibia;--3, the anterior tibial muscle;--4,
the long extensor of the toes;--5, the proper extensor of
the great toe;--6, the peroneus tertius;--7 and 8, the
peroneus longus and brevis;--9, the external head of the
gastrocnemius;--10, the internal head of the gastrocnemius;--11,
extensor brevis digitorum;--12, the superior annular ligament of
the dorsum of the foot.]
The _extensor longus digitorum_ (4, Fig. 84) arises from the external
tuberosity of the tibia, on the outer side of the tibialis anticus,
and from the upper three-fourths of the anterior surface of the
fibula. It descends vertically, and terminates in a tendon divided
into slips, which remain associated together (3, Fig. 85) to pass
beneath the anterior annular ligament. Immediately afterwards, these
slips spread out like a fan (4, Fig. 85) in the form of four tendons,
which pass over the dorsum of the foot to be inserted into the second
and third phalanges of the four outer toes. Each tendon behaves like
the corresponding extensor tendon in the hand. It forms a membranous
expansion on the dorsum of the first phalanx, joined by the tendons of
the extensor brevis digitorum, lumbricals, and interossei muscles, and
completes the capsule of the meta-tarso-phalangeal joint. Thereafter
each tendon splits into three parts--one central and two lateral. The
central slip is inserted into the intermediate phalanx, and the two
lateral slips, reunited, are attached to the base of the terminal
phalanx. Associated with the extensor longus digitorum is the _peroneus
tertius_, an essentially human muscle, which has a common origin with
the long extensor. Its tendon accompanies those of the last-named
muscle beneath the annular ligament, and is directed outwards on
the dorsum of the foot, to be inserted into the base of the fifth
metatarsal bone. With the tibialis anticus the long extensor of the
toes and peroneus tertius flex the foot on the leg, while at the same
time the common extensor extends the toes on the foot. In this action
it shows the prominence of its fleshy belly especially at the middle
of the leg, and the tendons on the back of the foot are raised up like
diverging cords. The peroneus tertius raises the outer border of the
foot in such movements as skating and dancing, and it is only then that
its prominence shows beneath the skin. Usually it is but little marked.
[Illustration: FIG. 85.
MUSCLES OF THE LEG (external surface).--1, 1, the anterior
tibial muscle;--2, 2, the tendon of the extensor proprius
hallucis;--3, 3, the extensor longus digitorum with its
tendons (4, 5, and 6);--7, the peroneus longus and its tendon
(8);--9, peroneus brevis and its tendon (10);--11, the external
head of the gastrocnemius;--12, 12, the soleus;--13, tendo
Achillis;--14, extensor brevis digitorum;--15, abductor minimi
digiti;--16, the rectus femoris;--17, 18, vastus externus;--19,
tendon of the biceps femoris;--20, external lateral ligament of
the knee.]
II. _External muscles_ (Fig. 85).--These are two in number, placed on
the outer side of the fibula, and called the _peroneal muscles_. They
are distinguished as the peroneus longus and peroneus brevis. They
completely cover the outer surface of the fibula, the peroneus longus
arising from the upper two-thirds, the peroneus brevis from the lower
two-thirds of the bone. The peroneus longus is behind and above, the
peroneus brevis in front and below. Their tendons descend together and
pass beneath the external annular ligament; that of the peroneus brevis
lying next the bone and grooving the back of the external malleolus.
Winding round the malleolus as on a pulley, they are directed forwards
on to the outer border of the foot. Then only the tendons separate from
each other, to be inserted into the foot at two points diametrically
opposite. One (that of the peroneus brevis) is directed horizontally
forwards, on the outer surface of the foot (10, Fig. 85), to be
inserted into the base or posterior extremity of the fifth metatarsal
bone; while the other, that of the peroneus longus, is directed
obliquely forwards and downwards so as to reach the sole of the foot,
beneath which it passes, lying in the groove of the cuboid bone; it
then runs obliquely across the sole of the foot, from the outer towards
the inner border, deeply hidden by the plantar muscles and ligaments,
and is finally inserted into the posterior extremity of the first
metatarsal bone and the under surface of the internal cuneiform bone.
These two muscles, but especially the peroneus brevis, extend and turn
the foot outwards, while at the same time they raise its external
border; so that their action is the reverse of that of the tibialis
anticus. But the peroneus longus has another important function which
explains why the muscle becomes prominent whenever a particular effort
is demanded of the foot, as, for example, when it is carried forward in
dancing, or in the act of imparting motion to an object. This muscle,
owing to the arrangement of its tendon, which passes like the string
of a bow across the hollow of the sole of the foot, acts by deepening
this hollow; it therefore raises the plantar arch, marked on the dorsal
surface by an increase of the curve of the foot.
III. _Posterior muscles_ (Figs. 82, 87).--The back of the leg is thick
and fleshy, and is formed by numerous and powerful muscles, divided
into two groups: the superficial group, which we shall describe in
detail, and the deep group, for which a few words will be sufficient.
The superficial group is formed by the _gastrocnemius_, _plantaris_,
and _soleus_ muscles.
The _gastrocnemius_ muscle (γαδτήρ, belly; κυήμη, leg) is responsible
for the surface form of the prominence of the calf. It consists of two
large, fleshy masses known as the inner and outer heads, which arise
respectively from the upper part of the inner and outer condyles of
the femur on their outer aspect. Overlapped by the insertions of the
hamstring muscles, the two heads of the gastrocnemius form the lower
boundaries of the popliteal space. They converge at its lower angle to
be inserted (separately) into a broad membranous tendon, which forms
the beginning of the _tendo Achillis_ (6, Fig. 87). At their origins,
each head possesses a tendon which covers its superficial surface. At
the insertion the tendon passes upwards for a considerable distance
on their deep surfaces. At its insertion into the tendo Achillis,
each fleshy head presents a rounded lower border; and it is to be
particularly noted that the inner head of the muscle usually descends
to a level lower than that of the outer head.
[Illustration: FIG. 86.
MUSCLES OF THE LEG (internal surface).--1, tibialis anticus;--2
and 3, its tendon;--4, tendon of the extensor proprius
hallucis;--5 and 6, internal head of the gastrocnemius;--7,
soleus;--8, tendo Achillis;--9, its attachment to the os
calcis;--10, tendon of the plantaris muscle;--11 and 12,
tendon of the tibialis posticus;--13 and 14, tendon of
the flexor longus digitorum;--15, tendon of the flexor
longus hallucis;--16, 16, abductor hallucis;--17, vastus
internus;--18, 19, 20, sartorius;--21, 22, gracilis;--23,
semi-membranosus;--24, semi-tendinosus.]
This muscle bends the knee and extends the foot on the leg. Through
the tendo Achillis it acts on the calcaneum or bone of the heel so
as to raise the heel and cause the living model, if erect, to rise
on the toes. Now the constitution of the muscle is such that its
external form is quite different when it is in repose and when it is
in contraction. Each head of the muscle, as already stated, possesses
at its origin a membranous tendon, which expands over the outer part
of the surface, but the inner part of each belly is fleshy. In a state
of repose the two halves of the muscle unite in the same rounded and
prominent shape, so that we cannot distinguish the part covered by the
aponeurotic expansion of tendon from the part formed by free muscular
fibres. But when the living model rises on the balls of the toes, or in
any other movement produced by a powerful contraction of the muscle,
we see the free fleshy part of each head swell up more strongly than
the part covered and tied down by the aponeurosis. At that moment,
therefore, the whole convex form of the calf presents a slight ovoid
surface on each side, and a long vertical prominence in the middle
line. This prominence is produced by the mesial muscular parts of the
two heads of the muscle, which approach each other during contraction,
and unite their double mass in a single median prominence. Fig. 82, by
the differences in shading, enables us to distinguish the aponeurotic
from the muscular parts, and to observe the important details of shape
into the study of which we have entered. The clear or aponeurotic
parts correspond to the two flat surfaces already mentioned, and the
shaded or fleshy parts correspond to the median prominence, with this
difference, that in the calf in contraction, this median prominence is
smoother than in Fig. 82, the two halves which compose it being merged
into a single mass, except at the angular space above the point where
they bound the popliteal space.
We will now return to what we have already said (see page 267) relative
to the posterior region of the knee, examined in the living model in
extension of the leg. If the model rises on the balls of the toes it is
no longer possible to speak of the popliteal space as _a hollow_
at the back of the knee. Under these conditions, the prominences
(already studied) of the biceps, semi-membranosus, and gastrocnemius
almost join each other, and the plantaris muscle, of which we will
speak immediately, helps to fill up the space; the region of the
popliteal space forms in reality a prominence, and the posterior
surface of the knee is marked in its central portion by a strong
muscular projection of which it is not possible to understand the cause
except by an attentive study of the muscles named.
The _soleus_ muscle, so called because its form has been compared to
that of a _sole_ (Latin--_solea_), is placed beneath the gastrocnemius,
which overlaps it, more on the inner (7, Fig. 86) than on the outer
border (12, Fig. 85) of the calf. In its action it is simple. It only
acts on the ankle-joint, as a powerful extensor of the foot. Arising
from the back of the fibula and from the tibia, its fibres are inserted
below into the deep surface of the tendo Achillis to within two inches
of the heel.
The _tendo Achillis_ is a strong band of fibrous tissue occupying
the lower part of the back of the leg. Membranous above, where it
is continued upwards on the deep surface of the bellies of the
gastrocnemius muscle, it becomes narrower and thicker below as it
approaches the heel. Broadening out slightly at its lower end, it
is inserted into the inferior half of the posterior surface of the
calcaneum, forming the prominence of the heel. In a muscular leg the
fibres of the soleus may be shown superficially, bulging beyond the
tendo Achillis at its outer and inner borders, below the outline of the
gastrocnemius, and more on the outer than on the inner side (5, Fig.
82, page 263).
The _plantaris_ is a small, insignificant muscle of which the fleshy
origin (6, Fig. 82) is from the outer condyle of the femur, under
cover of the outer head of the gastrocnemius muscle. Its small fleshy
belly is succeeded by a long, thin tendon (7, Fig. 82), which descends
obliquely between the gastrocnemius and the soleus to reach the inner
border of the tendo Achillis, along which it descends (10, Fig. 86).
Sometimes it is united with this tendon early in its course, and
sometimes it reaches the calcaneum, or it may join the internal annular
ligament at the ankle.
The deep muscles of the back of the leg are not visible on the model
except on the inner side above the ankle. Here, on the inner side
of the tendo Achillis (8, Fig. 82), is placed a series of tendons,
proceeding in the interval between the internal malleolus and the
calcaneum to the foot. The muscles are the _tibialis posticus_, the
_flexor longus digitorum_, and the _flexor longus hallucis_. The
fleshy bellies of these muscles, deeply hidden beneath the superficial
muscles, arise from the posterior surface of the tibia, from the
fibula, and from the interosseous membrane. Their tendons descend
obliquely over the back of the internal malleolus, where those of the
tibialis posticus and the common flexor of the toes alone are visible
(the tendon of the flexor proprius hallucis being almost entirely
hidden beneath the tendo Achillis). From this they are reflected over
the internal malleolus and pass into the sole of the foot, bound down
on the inner side of the ankle by the dense band of the _internal
annular ligament_. The tibialis posticus is almost immediately
inserted by radiating bands into most of the tarsal and metatarsal
bones (12, Fig. 86), and the other two tendons reach the toes, where
they are inserted in the same manner as we have already described for
the tendons of the flexor longus pollicis and the deep flexor of the
fingers in the hand.
[Illustration: FIG. 87.
THE MUSCLES OF THE CALF.--1, biceps;--2, semi-tendinosus;--3,
popliteal space;--4, gastrocnemius;--5, 5, soleus;--6, tendo
Achillis;--7, os calcis;--8, peroneus longus;--9, tibialis
posticus and flexor longus digitorum.]
_MUSCLES OF THE FOOT._--The muscles of the foot include not only the
muscles of the plantar region, corresponding to the palm of the hand,
but also the tendons on the dorsum of the foot, and a special extensor
muscle, the _extensor brevis digitorum_.
The tendons of muscles on the dorsum of the foot have already been
described (p. 270). The _extensor brevis digitorum_ muscle (11,
Fig. 84, and 14, Fig. 85) consists of a short, fleshy belly placed
obliquely on the dorsum of the foot, and extending from behind inwards
and forwards. It origin is rounded and attached to the upper surface
of the calcaneum in the _cavity or canal of the tarsus_ (page 155),
external to the astragalus. From this origin it is directed forwards
and inwards; becoming broader, it passes beneath the tendons of the
common extensor and immediately divides into four muscular slips,
each of which has a tendon attached to it. These tendons pass under
those of the common extensor, so as to form with them a figure with
lozenge-shaped spaces, and proceed to the four inner toes to be
inserted, in the case of the great toe, into the base of the first
phalanx; uniting, in the case of the second, third, and fourth toes,
with the expansions of the extensor tendons on the dorsum of the
phalanges. This muscle aids in the extension of the toes, and by
its obliquity counteracts the action of the long extensor. When it
contracts, the portion of the muscle situated on the outer side of
the tendons of the long extensor become very prominent, not being
tied down by anything, and this prominence is still clearer because
behind it is a depression, more or less evident, corresponding to the
calcaneo-astragaloid cavity of the tarsus.
We will not describe at length the muscles of the sole of the foot with
regard to form. The foot derives most of its characteristics from its
bony structure; the muscles of the sole round off by their presence
the angles of the skeleton and fill up the cavities, but do not modify
essentially the bony forms. On the other hand, these numerous muscles
are in general but poorly developed, and they are to a large extent
united into common masses, which makes it difficult, except for the
skilled anatomist, to isolate and recognise distinctly each fleshy
belly. It is therefore useless for an artist to enter into a detailed
study of these muscles, which reproduce in their general arrangement
the distribution of the muscles of the hand. We will content ourselves,
then, by saying that the sole of the foot, like the palm of the hand,
possesses three muscular masses--1st. An internal group (16, Fig.
86), belonging to the great toe, formed by the _abductor hallucis_,
which arises from the calcaneum, and by the _flexor brevis_, the
_adductor transversus_, and _adductor obliquus hallucis_, which arise
from the anterior bones of the tarsus and from the metatarsus; 2nd.
An external group (15, Fig. 86), belonging to the little toe, formed
by the _abductor_, which arises from the calcaneum, and the _flexor
brevis_, from the cuboid; 3rd. Finally, a central mass, formed by the
_flexor brevis digitorum_, the _long flexor tendons_, _lumbricals_, and
_interossei_--which in a sense repeat what we have said regarding the
muscles of the same name, more easily studied, in the hand.