A. ON THE VENTRAL SIDE.--=M. gastrocnemius.=--This is the great muscular
mass of the calf. It arises by two heads, the caput laterale or lateral
head (Fig. 90, _m_), and the caput mediale or medial head (Fig. 91,
_k_), of the gastrocnemius.
=Caput laterale= (Fig. 90, _m_, _m′_, _m″_).--The origin of the lateral
head is in four portions:
(1) From the tendon of origin of the plantaris which comes from the
middle of the lateral border of the patella. The tendon ends in a small
conical mass of fibres (_m′_) which joins the ventral part of the common
head.
(2) By a slender flat tendon, distad of the first, from the superficial
fascia of the shank (_m″_). The tendon ends in a conical mass which
joins the dorsal border of the common head.
(3) By a strong tendon and by muscle-fibres from the distal border of
the lateral sesamoid bone (Fig. 61, 3) of the femur. These fibres (_m_)
form the middle and outer part of the common head.
(4) By muscle-fibres from the middle of the outer surface of the
aponeurosis covering the plantaris (Fig. 90, _l_) along rather more than
the proximal half of the tibia. The lateral head thus formed is flat and
fusiform in section.
=Caput mediale= (Fig. 91, _k_; Fig. 92, _j_).--The medial head resembles
the lateral head closely.
_Origin_ by a strong tendon from the medial sesamoid bone of the femur
(Fig. 61, 4) and by muscle-fibres from the surface of the shaft for a
short distance proximad of this.
The two heads unite by their contiguous borders at the junction of the
first and second thirds of the tibia. The common muscle narrows rapidly
and ends in a flat tendon which joins the tendon of the soleus to form
the so-called tendon of Achilles (tendo calcaneus) (Fig. 90, _t_). This
has its
_Insertion_ into the proximal end of the calcaneus (Fig. 90, 4) near its
ventral border. This tendon together with that of the soleus (Fig. 90,
_o_) and the fascia of the shank forms a tubular sheath for the tendon
of the plantaris.
_Relations._--(1) Of the lateral head. Lateral (outer) surface with the
biceps femoris (Fig. 68, _t_) and the superficial fascia. Medial (inner)
surface with the popliteus (Fig. 92, _k_), the plantaris (Fig. 90, _l_)
(to which it is closely united), the medial head of the gastrocnemius
(Fig. 91, _k_), the soleus (Fig. 90, _o_), and the peroneus longus (Fig.
90, _q_). (2) Of the medial head. Medial (outer) surface with the
superficial fascia and the tendons of the gracilis (Fig. 91, _b_),
semimembranosus (Fig. 92, _h′_), and semitendinosus (Fig. 92, _i_).
Lateral (inner) surface at the origin with the adductor femoris (Fig.
92, _g_), then with the plantaris (Fig. 91, _l_), the popliteus (Fig.
92, _k_), flexor longus digitorum (Fig. 91, _n_), and the lateral head
of the gastrocnemius (Fig. 90, _m_).
_Action._--Extensor of the foot. (It is to be noted that what is called
=extension= in the foot is analogous to what is called =flexion= in the
hand, so that the extensors of the foot are most readily to be compared
with the flexors of the hand.)
=M. plantaris= (Fig. 90, _l_; Fig. 91, _l_).--A fusiform muscle covered
distally by the gastrocnemius, but appearing between the two heads of
the gastrocnemius at their proximal ends (Fig. 90, _l_).
_Origin_ by a strong tendon from the middle of the lateral border of the
patella and by fleshy fibres from the ventral border of the lateral
sesamoid.
The patellar tendon ends in a flattened head which passes ventrad over
the lateral epicondyle of the femur and then curves distad; it is
closely united with the lateral head of the gastrocnemius. The muscle
ends in a thick tendon which passes through a sheath formed by the
tendons of the gastrocnemius and soleus, and the fascia of the shank.
The tendon passes over the grooved proximal end of the calcaneus onto
its ventral surface. It is held in place against the groove by two
sheets of aponeurosis, which leave the tendon on either side for a
distance of more than a centimeter and are attached to the lateral
surfaces of the calcaneus at its proximal end. Lateral motion is thus
hindered, while longitudinal motion is permitted.
Between this tendon and the tendon of Achilles is a synovial bursa which
aids the gliding movement of the tendon. In the sole of the foot
opposite the distal end of the calcaneus the tendon broadens and ends in
the flexor brevis digitorum (pedis perforatus) muscle, which might also
be considered as a second part of the plantaris. In man the plantaris is
inserted into the calcaneus along with the gastrocnemius.
_Relations._--The muscle is covered throughout by the two heads of the
gastrocnemius (Fig. 90, _m_; Fig. 91, _k_), except at the proximal end
(Fig. 90, _l_), where it is in contact with the integument. Inner
surface in relation with the popliteus (Fig. 92, _k_), the soleus (Fig.
90, _o_), the flexor longus digitorum (Fig. 91, _n_), and flexor longus
hallucis (Fig. 91, _m_).
=M. soleus= (Fig. 90, _o_).--A flat fusiform muscle lying beneath the
plantaris.
_Origin_ by muscle-fibres from the lateral surface of the head of the
fibula, and by tendon-fibres from the proximal two-fifths of its ventral
border.
_Insertion._--The muscle ends in a slender tendon which joins the
lateral border of the gastrocnemius tendon to form the tendon of
Achilles (Fig. 90, _t_), which forms the sheath of the plantaris tendon.
_Relations._--Outer surface with the gastrocnemius (Fig. 90, _m_) and
plantaris (Fig. 90, _l_). Inner surface with the peroneus longus (Fig.
90, _q_), peroneus tertius (Fig. 90, _r_), and flexor hallucis (Fig. 91,
_m_).
_Action._--Assists the gastrocnemius to extend the foot.
=M. triceps suræ.=--The gastrocnemius and the soleus are sometimes
considered as forming a single muscle, with three heads, under the name
triceps suræ.
=M. popliteus= (Fig. 92, _k_).--A triangular muscle passing from the
femur obliquely toward the medial side over the ventral surface of the
proximal end of the tibia.
_Origin_ by a strong tendon from the popliteal groove on the surface of
the lateral epicondyle of the femur. In the tendon is a sesamoid bone,
the popliteal bone (Fig. 61, 5, page 89), which glides over the ventral
part of the lateral articular facet on the proximal end of the tibia. As
the muscle passes over the joint it is closely attached to the joint
capsule. From the popliteal bone, which with the tendon lies within the
capsule of the knee-joint, the muscle-fibres diverge to their
_Insertion_ into the proximal end of the ventral surface of the tibial
shaft on the medial side of the medial oblique ridge. The area of
insertion extends slightly onto the medial surface of the bone.
_Relations._--Outer surface with the gastrocnemius (Fig. 92, _j_) and
plantaris (Fig. 91, _l_), and with the tendon of the semitendinosus
(Fig. 92, _i_). Distal border with the origins of the soleus and flexor
longus digitorum. Inner surface with the capsule of the knee-joint and
the tibia.
_Action._--Rotates the thigh so as to turn the toes inward.
* * * * *
The three following deep muscles on the ventral surface of the shank are
covered by a deep fascia (the deep crural fascia) which separates them
from the overlying muscles. This fascia stretches from the dorsal border
of the tibia about the ventral side of the shank to the medial border of
the tibia. It sends a slip beneath the border of the fibula.
=M. flexor longus digitorum= (Fig. 91, _m_ and _n_).--Owing to the
reduction of the first digit in the cat the tendon of the flexor longus
hallucis (_m_) has become united to that of the flexor longus digitorum
(_n_), so that the two might be considered separate heads of a single
muscle. The head corresponding to the flexor longus hallucis (_m_) is
much larger than that corresponding to the flexor longus digitorum
(_n_). The two heads will be described separately.
(1) =M. flexor longus hallucis= (Fig. 91, _m_).--This lies against the
ventral surface of the tibia and fibula beneath the popliteus (Fig. 92,
_k_) and soleus (Fig. 90, _o_).
_Origin_ by fleshy fibres, (1) from the sheet of deep crural fascia
which dips between it and the tibialis posterior (Fig. 91, _o_) and the
flexor longus digitorum (_n_). (2) From the ventral surface of the tibia
distad of the lateral oblique line to within one to three centimeters of
the distal end of the shaft. (3) From the medial surface of the shaft
and head of the fibula and from the whole interosseous ligament. On the
fibular side the origin may extend onto the tendon of the popliteus and
the fascia of the peroneus longus. The fibres form a flat fusiform mass
ending one centimeter from the heel in a strong flat tendon (_m′_) which
passes over the groove on the distal surface of the astragalus and over
the groove on the sustentaculum tali. The two grooves are converted into
a continuous canal by strong transverse ligaments, and the canal is
lined by an extension of the synovial bursa of the ankle-joint. Emerging
from the canal the tendon broadens and receives on its medial side the
insertion of the tendon of the flexor longus digitorum (_n_). The tendon
gives origin on its outer surface to the lumbricales and to the common
plantar ligament. The tendon continues to broaden until it reaches the
middle of the length of the metacarpals; here it divides into four
tendons which pass to the terminal phalanges of the digits.
_Insertion._--The relations of the four tendons and their insertions are
identical with those of the flexor profundus digitorum of the hand.
_Relations._--Outer surface with the soleus (Fig. 90, _o_) and plantaris
(Fig. 91, _l_). Lateral border with the soleus, the peroneus tertius
(Fig. 90, _r_), and peroneus brevis (Fig. 90, _s_). Medial border with
the tibialis posterior (Fig. 91, _o_) and flexor longus digitorum (Fig.
91, _n_).
_Action._--Flexor of the phalanges.
(2) =M. flexor longus digitorum= (Fig. 91, _n_).
_Origin_ by muscle- and tendon-fibres from the ventral surface of the
tibia over its proximal half between the oblique ridges; by fleshy
fibres from an aponeurosis between it and the tibialis posterior (Fig.
91, _o_), and by tendon from the medial surface of the head of the
fibula. At the junction of the middle and distal thirds of the bone the
muscle ends in a slender tendon which passes through the ventral groove
on the medial surface of the tibia and, curving onto the sole of the
foot, becomes attached to the medial border of the common tendon
described under the last.
_Relations._--Outer surface with the medial head of the gastrocnemius
(Fig. 91, _k_) and with the superficial fascia. Inner surface with the
tibialis posterior (Fig. 91, _o_). Medial border at the proximal end
with the popliteus (Fig. 92, _k_), lateral border with the tibialis
posterior (Fig. 91, _o_), and flexor longus hallucis (Fig. 91, _m_).
_Action._--Flexor of the phalanges.
=M. tibialis posterior= (Fig. 91, _o_).--A slender flat fusiform muscle
beneath the flexor longus digitorum and between it and the flexor longus
hallucis.
_Origin_ by fleshy fibres from nearly the whole medial surface of the
head of the fibula, from the inner surface of the aponeurosis between it
and the flexor longus digitorum (_n_), and by a few fleshy fibres from
the ventral surface of the tibia between the oblique ridges. Some fibres
may also arise from the outer surface of the aponeurosis covering the
flexor longus hallucis (_m_). The muscle ends at about the middle of the
tibia in a slender flat tendon which passes parallel to the tendon of
the flexor longus digitorum (_n_) through the dorsal groove on the
medial surface of the distal end of the tibia. This groove is converted
into a canal by a transverse ligament. Beyond the canal the tendon turns
onto the plantar surface of the foot and passes through a groove on the
ventral surface of the scaphoid bone. It then divides.
_Insertion_ into the outer tuberosity on the surface of the scaphoid,
and onto the proximal end of the ventral surface of the medial
cuneiform.
_Relations._--Outer and medial surface with the flexor longus digitorum
(_n_). Lateral surface with the flexor longus hallucis (_m_).
_Action._--Extensor of the foot.
B. MUSCLES ON THE DORSAL AND LATERAL SURFACES OF THE LOWER LEG.--=M.
peroneus longus= (Fig. 90, _q_).--A slender, fusiform muscle lying
superficially on the lateral side of the leg, dorsad of the soleus.
_Origin_ by tendon-fibres from the lateral surface of the head of the
fibula and from the proximal half of the lateral surface of its shaft.
At the junction of the middle and distal thirds of the lower leg the
muscle ends in a slender tendon which passes through the groove on the
lateral surface of the lateral malleolus. This groove is converted into
a canal by a transverse ligament. The tendon passes through the groove
on the peroneal tubercle of the calcaneus, then turns onto the sole of
the foot and passes through the peroneal groove on the cuboid bone. It
then turns mediad and passes through the groove between the ventral
processes of the lateral cuneiform and the metatarsal until it reaches
the first metatarsal. The entire groove is converted into a canal by the
overlying ligaments.
_Insertion_ into (1) the base of the fifth metatarsal, and (2) the outer
side of the base of the first metatarsal, and (3) by slender branches
into the bases of the other metatarsals.
_Relations._--Outer (lateral) surface with the superficial fascia and
the tendon of the biceps femoris. Inner surface with the peroneus
tertius (_r_) and peroneus brevis (_s_), and with the extensor longus
digitorum (_p_). At the proximal end the dorsal border touches the
tibialis anterior (_n_).
_Action._--Flexor of the foot.
=M. peroneus tertius= (Fig. 90, _r_).--A slender fusiform muscle beneath
the peroneus longus (_q_).
_Origin_ by fleshy fibres from about the second quarter of the lateral
surface of the fibula. The muscle ends in a slender tendon (_r′_), which
passes with that of the peroneus brevis (_s_) through the groove on the
ventral border of the lateral malleolus. The groove is converted into a
canal by a transverse ligament. Emerging from it, the tendon turns and
passes along the outer margin of the foot. In passing the sesamoid at
the base of the first phalanx of the fifth digit it is united to it by a
band which passes from the sesamoid to the tendon.
The _insertion_ is finally into the lateral border of the extensor
tendon of the fifth digit as it passes from the first to the second
phalanx.
_Relations._--Outer surface with the peroneus longus (_q_), the soleus
(_o_), and the superficial fascia. Ventral border with the soleus (_o_)
and flexor longus hallucis (Fig. 91, _m_). Inner surface with the
peroneus brevis (Fig. 90, _s_).
_Action._--Extensor and abductor of the fifth digit and flexor of the
foot.
=M. peroneus brevis= (Fig. 90, _s_) lies beneath the other peronei.
_Origin_ by fleshy fibres from the distal half of the surface of the
fibula, which it embraces. At the lateral malleolus the muscle ends in a
thick tendon which passes through the canal on the ventral surface of
the malleolus. In the canal it is enlarged and surrounded by a synovial
bursa. It then turns onto the foot and passes over the dorsal surface of
the calcaneus on its lateral side and has its
_Insertion_ into the tubercle on the lateral side of the base of the
fifth metatarsal.
_Relations._--Outer surface with the peronei longus (_q_) and tertius
(_r_). Inner surface with the bone.
_Action._--Extensor of the foot.
=M. extensor digitorum longus= (Fig. 90, _p_).--A fusiform muscle which
lies beneath the tibialis anterior (_n_), against the interosseous
membrane, and between the tibialis anterior and the peronei.
_Origin_ by a thin flat tendon from the lateral surface of the lateral
epicondyle of the femur just dorsad of the origin of the popliteus. The
tendon becomes narrower and thicker and passes through the capsule of
the knee-joint and over a slight groove on the tibia just dorsad of the
head of the fibula. The belly of the muscle extends the entire length of
the tibia, passing beneath the transverse ligament (5) along with the
tendon of the tibialis anterior (_n_). At the ankle it runs through a
fibrous loop which is attached to the dorsal surface of the calcaneus
(the annular ligament of the calcaneus); it then turns and passes onto
the dorsum of the foot. The muscle ends in four slender tendons, the two
middle of which begin at the transverse ligament, while the others begin
at the fibrous loop. The tendons diverge to the four digits. Each tendon
is connected with the fibrous sheath surrounding the base of the first
phalanx, and each has a synovial bursa beneath it at this point. Near
the distal end of the first phalanx the tendon is united on the lateral
side to the conjoined tendon of the extensor brevis digitorum and an
interosseus muscle, and on the medial side to the tendon of the
interosseus. The lateral side of the most lateral tendon is not thus
united, but is joined on the outer side by the tendon of the peroneus
tertius.
_Insertion._--The tendon thus formed on the dorsum of each phalanx by
the junction of the two or three tendons above mentioned is firmly
attached to the base of the second phalanx at its proximal end in the
middle of its dorsal surface. In crossing the joint between the first
and second phalanges the tendon forms a fibrous pad which protects the
dorsum of the joint and glides over it. It then continues to be inserted
into the base of the terminal phalanx.
_Relations._--Outer surface with the tibialis anterior (_n_) and the
superficial fascia. Inner surface with a part of the tibialis
anterior, with the bones, the interosseous membrane, and the peroneus
brevis (_s_).
_Action._--Extensor of the phalanges.
=M. tibialis anterior= (Fig. 90, _n_).--This is the superficial muscle
covering the lateral side of the tibia.
_Origin_ by fleshy fibres from the proximal one-sixth of the lateral
surface of the shaft of the tibia, from the proximal third of the medial
border of the shaft and head of the fibula, and from the intervening
interosseous ligament. The triangular body of the muscle covers the
lateral surface of the tibia and the outer surface of the extensor
longus digitorum (_p_). Near the malleolus it ends in a strong tendon
which passes beneath the transverse ligament along with the tendon of
the extensor longus (_p_). The tendon crosses the dorsal surface of the
foot obliquely toward its medial side.
_Insertion_ into the outer surface of the first metatarsal.
_Relations._--Outer surface with the superficial fascia and the tendon
of the biceps femoris. Inner surface with the extensor longus (_p_), the
tibia, and the interosseous membrane.
_Action._--Flexor of the foot.