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The Muscles in the Sole of the Foot. The muscles in the sole of the foot are divisible into four layers placed deep to the plantar aponeurosis.

The first layer includes the abductor hallucis, flexor digitorum brevis, and abductor digiti quinti. The second layer consists of the lumbricales and quadratus plantæ, together with the tendons of the flexor hallucis longus and flexor digitorum Iongus. The third layer comprises the flexor hallucis brevis, adductor hallucis, and

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Fig. 386.--MUSCLE-ATTACHMENTS TO LEFT Tarsus AND METATARSUS (Plantar Aspect).

flexor digiti quinti brevis. The fourth layer consists of the interossei (plantar and dorsal), placed between the metatarsal bones : and the tendons of insertion of the tibialis posterior and peronæus longus.

FIRST LAYER. M. Abductor Hallucis.— The abductor hallucis has a double origin: (1) by a short tendon from the medial side of the medial process of the tuberosity of the

neus (Fig. 386), and (2) by fleshy fibres from the ligamentum laciniatum, the plantar aponeurosis which covers it, and the intermuscular septuin between it and the flexor digitorum brevis.

The muscle lies superficially, along the medial border of the sole ; its tendon is

inserted, along with part of the flexor hallucis brevis into the medial side of the base of the first phalanx of the great toe.

Nerve-Supply.—Medial plantar nerve (L. 4. 5. S. 1.).
Actions. A flexor and abductor of the great toe.

M. Flexor Digitorum Brevis.—The flexor digitorum brevis has likewise a double origin : (1) from the anterior part of the medial process of the tuberosity of the calcaneus (Fig. 386, p. 432), and (2) from the thick central part of the plantar aponeurosis which covers it, and from the intermuscular septa on either side.

It passes forwards, and gives rise to four slender tendons, which are inserted into the second

Plantar phalanges of the four lateral

aponeurosis toes, after having been perforated by the long flexor tendons, just as in the case of the tendons of ABDUCTOR DIGITI the flexor digitorum sublimis of

QUINTI the hand (p. 389).

QUADRATUS

PLANTE
Nerve-Supply.- Medial plantar
nerve (L. 4. 5. S. 1.).
Actions.—The muscle is a flexor

FLEXOR
of the toes, acting on the metatarso-
phalangeal and first inter-phalangeal ABDUCTOR
articulations of the four lateral toes.

HALLUCIS
M. Abductor Digiti Quinti.

FLEXOR DIGITI
-The abductor digiti quinti

QUINTI BREVIS also has a double origin : (1) by

FLEXOR HALLUCIS fleshy and tendinous fibres from the anterior part of both pro

FOURTH cesses of the tuberosity of the calcaneus, partly concealed by the flexor digitorum brevis (Fig. 386, p. 432), and (2) by fleshy fibres

FIRSTfrom the lateral portion of the plantar aponeurosis and the cal- FLEXOR

HALLUCIS LONGUS caneo - metatarsal ligament, and from the intermuscular septum between it and the flexor digitorum brevis.

Its tendon lies along the fifth metatarsal bone, and is inserted into the lateral side of the posterior end of the first phalanx of the little toe. The most lateral fibres usually obtain additional insertion into the lateral side of the plantar surface of the fifth metatarsal bone.

Fig. 387.-SUPERFICIAL MUSCLES OF THE Right Foot.
Nerve-Supply.-Lateral plantar nerve (S. 1. 2.).
Actions. - Flexion and abduction of the little toe.

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SECOND LAYER. The tendons of the long flexors of the toes, the lumbricales and quadratus plantæ muscles, constituting the second layer of muscles, have already been described (p. 430). They lie deep to the abductor hallucis and the flexor digitorum brevis, and occupy the hollow of the tarsus and the space between the first and fifth metatarsal bones; their deep surfaces are in contact with the adductor of the

great toe and the interossei muscles.

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THIRD LAYER.

M. Flexor Hallucis Brevis. — The flexor hallucis brevis arises by tendinous fibres from (1) the medial part of the plantar surface of the cuboid bone (Fig.

386, p. 432), and (2) the tendon of the Long plantar ligament

tibialis posterior. Directed forwards, over FLEXOR HAL

the first metatarsal bone, the muscle LUCIS LONGUS FLEXOR DIGI

separates into two parts, between which TORUM LONGUS

is the tendon of the flexor hallucis longus. QUADRATUS PLANTE

Each portion gives rise to a tendon (origins)

which is inserted into the corresponding PERONÆUS

side of the base of the first phalanx LONGUS

of the great toe; in each tendon, under the metatarso-phalangeal articulation, a sesamoid bone is developed. The medial tendon is

united with the insertion of the FLEXOR DIGITI

abductor, the lateral tendon with QUINTI BREVIS

the insertions of the adductor

muscle of the great toe. FLEXOR HALLUCIS BREVIS

Nerve - Supply. - Medial plantar INTEROSSEOUS

nerve (L. 4. 5. S. 1.). MUSCLES

Actions.—A flexor of the metatarsoADDUCTOR HALLUCIS

phalangeal joint of the great toe. (oblique head)

M. Adductor Hallucis.- The ADDUCTOR

adductor hallucis consists of two (transverse head)

parts. The oblique head of the muscle arises (1) from the sheath of the peronæus longus, and (2) from the plantar surfaces of the bases of the second, third, and fourth metatarsal bones (Fig. 386, p. 432). It lies in the hollow of the foot, on a deeper plane than the long flexor tendons and lumbricales, and on the lateral side of the flexor hallucis brevis, and it runs obliquely medially and forwards, to be inserted on the

lateral side of the base of the first Fig. 388.- DEEP MUSCLES OF THE SOLE OF THE Foot. phalanx of the great toe between

and along with the flexor brevis and the transverse head of the adductor hallucis.

The transverse head arises from (1) the capsules of the lateral four metatarsophalangeal articulations and (2) the transverse metatarsal ligament.

It runs transversely medially under cover of the fexor tendons and lumbricales, the muscle is inserted, along with the oblique head, into the lateral side of the base of the first phalanx of the great toe.

Nerve-Supply.-Lateral plantar nerve (S. 1. 2.).
Actions.-Flexion and adduction of the great toe towards the middle line of the foot.

M. Flexor Digiti Quinti Brevis.—The flexor digiti quinti brevis arises from (1) the sheath of the peronæus longus and (2) the base of the fifth metatarsal bone (Fig. 386, p. 432).

Partially concealed by the abductor digiti quinti, the muscle passes along the fifth metatarsal bone, to be inserted, in common with that muscle, into the lateral side of the base of the first phalanx of the little toe.

Nerve-Supply.-Lateral plantar nerve (S. 1. 2.).
Actions.-Flexion of the little toe.

THE
PLANTAR
INTER-
OSSEI

FOURTH LAYER. Mm. Interossei.-The interossei muscles of the foot resemble those of the hand except in one respect. In the hand the line of action of the muscles is the middle line of the middle finger. In the foot the second toe is the digit round which the muscles are grouped, and their attachments and their actions DORSAL differ accordingly.

There are four dorsal and three plantar muscles, which occupy together the four interosseous spaces, and project into the hollow of the foot. The four

Fig. 389.-INTEROSSEOUS MUSCLES OF THE Right Foot. dorsal muscles, one in each interosseous space, arise by two heads each from the shafts of adjacent metatarsal bones.

Each gives rise to a tendon, which, after passing dorsal to the transverse metatarsal ligament, is inserted on the dorsum of the foot, into the side of the first phalanx, the metatarso-phalangeal capsule, and the dorsal expansion of the extensor tendon. The first and second muscles are inserted respectively into the medial and lateral sides of the proximal end of the first phalanx of the second toe. The third and fourth muscles are inserted into the lateral sides of the third and fourth toes.

The three plantar muscles occupy the three lateral interosseous spaces. Each arises, by a single head, from the medial side of the third, fourth, and fifth metatarsal bones respectively.

Each ends in a tendon which passes dorsal to the transverse metatarsal ligament, and is inserted, in the same manner as the dorsal muscles, into the medial sides of the third, fourth, and fifth toes.

Nerve-Supply. Lateral plantar nerve (S. 1. 2.).

Actions. The muscles are flexors of the metatarso-phalangeal joints, and extensors of the inter-phalangeal joints of the four lateral toes. The dorsal interossei abduct the toes into which they are inserted from the middle line of the second toe. The plantar interossei adduct the three lateral toes towards the second toe.

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Actions of the Muscles of the Leg and Foot. The muscles of the leg and foot act chiefly in the movements of the ankle-joint (assisted by movements of the intertarsal joints); of the metatarso-phalangeal joints (assisted by movements of the tarso-metatarsal and inter-metatarsal joints); and of the inter-phalangeal joints.

I. Tibio-Fibular Articulations.—The proximal tibio-fibular articulation is only capable of slight gliding movement, occasioned by the action of the biceps and popliteus and the muscles arising from the fibula.

II. Movements at the Ankle-Joint. -The movements at the ankle-joint are movements of flexion and extension of the foot on the leg, along with inversion and eversion (only during extension). These movements are produced at the ankle, aided by movements in the intertarsal joints, and are occasioned by the foÎlowing muscles :

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III. Movements of the Toes.-A. At the Metatarso-Phalangeal Joints (assisted by movements at the tarso-metatarsal and inter-metatarsal joints).—These movements are flexion and extension, abduction and adduction in a line corresponding to the axis of the second toe).

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B. At the inter-phalangeal joints the movements are limited to flexion and extension.

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Movements of the Lower Limb generally. The characteristic features of the lower limb are stability and strength, and its muscles and joints are both subservient to the functions of transmission of weight and of locomotion. In the standing position the centre of gravity of the trunk falls between the heads of the femora, and is located about the middle of the body of the last lumbar vertebra. It is transmitted from the sacrum through the posterior sacro-iliac ligaments to the hip bone, and through the bones of the lower limb to the arch of the foot, where the talus distributes it backwards through the calcaneus to the heel, and forwards through the tarsus and metatarsus to the balls of the toes.

Locomotion. The three chief means of progression are walking, running, and leaping. In walking, the body and its centre of gravity are inclined forwards, the trunk oscillates from side to side as it is supported alternately by each foot, the arms swing alternately with the corresponding leg, and one foot is always on the ground. The act of progression is performed by the leg, aided in two ways by gravity. The movements of the leg occur in the following way. At the beginning of a step, one leg, so to speak, “shoves off”; the heel is raised and the limb is extended. "By the action of the muscles flexing the hip and knee-joints, and extending the ankle-joint and toes, this limb is raised from the ground sufficiently to clear it, and passes forwards by the action of gravity, aided by the force given to the movement by the extensor muscles. After passing the

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