deep to M. gastrocnemius pars externa; bounded medially by medial head
of M. flexor perforatus digiti III, anterolaterally by posterior head of
M. flexor perforans et perforatus digiti II, and anteriorly by M. flexor
digitorum longus; divided into three heads--medial (largest), lateral,
and anterolateral (smallest); tendon of insertion of M. extensor
iliofibularis passing between medial and lateral heads; proximal and
anteroproximal parts of _lateral head_ an extremely thin, flat tendon;
anterodistal part of tendon fused to lateral surface of fleshy part of
underlying lateral head of M. flexor perforatus digiti II; proximal part
of tendon fused indistinguishably to tendinous part of underlying
lateral head of M. flexor perforatus digiti II; fleshy part of
_anterolateral head_ anterodistal to lateral head; proximal part of
former a long slender tendon anterior to lateral head; anterior surface
of anterolateral head (both fleshy and tendinous parts) fused to tendon
of anterolateral head of M. flexor perforatus digiti III; deep surface
fused to underlying anterolateral head (fleshy) of M. flexor perforatus
digiti II; common tendon of anterolateral heads of M. flexor perforatus
digiti IV and M. flexor perforatus digiti III passing medial to tendon
of insertion of M. extensor iliofibularis, to peroneal nerve, and to
fibular arm of guide loop for M. extensor iliofibularis; tendon of M.
ambiens inserting on anterolateral surface of this common tendon;
_medial head_ entirely fleshy; medial surface fused to medial head of M.
flexor perforatus digiti III; deep surface fused to medial edge of
underlying medial head of M. flexor perforatus digiti II; medial and
lateral heads joined, forming bipinnate belly (pinnate structure most
evident on deep surface); anterolateral head joined to distolateral part
of belly.
ORIGIN.--The _medial head_ attaches fleshily to the proximal part of the
popliteal area proximal (adjacent) to the origin of M. flexor hallucis
longus and distolateral to the distal end of the origin of M.
femorocruralis; the attachment extends laterally onto the posterolateral
surface of the femur proximal (adjacent) to the common attachment of M.
gastrocnemius pars externa and the distal arm of the guide loop for M.
extensor iliofibularis; the medial edge of the origin is fused with part
of the tendinous origin of the medial head of M. flexor perforatus
digiti III.
The broad flat common tendon of the _lateral head_ and the lateral head
of M. flexor perforatus digiti II fuses to the superficial surface of
the fibular arm of the guide loop for M. extensor iliofibularis and
contributes to the femorofibular fascia; consequently the ultimate
origin would be the external femoral condyle and the head of the fibula.
The slender common tendon of the _anterolateral head_ and the
anterolateral heads of Mm. flexor perforatus digiti II and flexor
perforatus digiti III passes deep to the insertional tendon of M.
extensor iliofibularis and to the fibular arm of the guide loop for the
latter muscle (to which it partly fuses); the tendon attaches to a
narrow line on the head of the fibula adjacent to the attachment of the
fibular arm of the guide loop and to the deep part of the femorofibular
fascia.
INSERTION.--The slender ossified tendon becomes flexible before it
passes posterior to the tibial cartilage deep to the tendon of M.
gastrocnemius, lateral to the tendon of M. flexor perforans et
perforatus digiti III, and superficial to the lateral half of the tendon
of M. flexor perforatus digiti III; a thin sheet of connective tissue
covers the tendon and attaches by its edges to the underlying tendon of
M. flexor perforatus digiti III (thus the latter tendon forms a sheath
for the tendon of M. flexor perforatus digiti IV; this sheath is
separate from a similar sheath surrounding the tendon of M. flexor
perforans et perforatus digiti III); the tendon is again ossified where
it passes along the posterolateral surface of the tarsometatarsus
posterolateral to the tendon of M. flexor perforans et perforatus digiti
III; near the distal end of the tarsometatarsus the tendon becomes
flexible and expands greatly in width and thickness, and sends a small
slip dorsally, medial to the underlying tendons, that attaches to the
subarticular cartilage ventral to the trochlea for digit IV; sometimes
this slip is continuous with the retinaculum ventral to the tendon at
the level of the proximal end of the digit. Several more or less
distinct sheets of tough connective tissue lie ventral to all of the
flexor tendons at the level of the trochleae and the proximal end of the
digits, holding them in place. The tendon narrows as it passes onto the
ventral surface of digit IV and soon divides into three branches; the
tendon of M. flexor digitorum longus emerges between the medial and
middle branches. The lateral branch attaches to the subarticular
cartilage ventral to the first interphalangeal joint and is also bound
by connective tissue to the ventrolateral surface of the first phalanx.
A dorsal slip arises at the point of divergence of the lateral and
middle branches and attaches to the subarticular cartilage of the first
interphalangeal joint. The middle branch attaches to the subarticular
cartilage of the second joint. The medial branch, after sending dorsal
slips to each of the first two subarticular cartilages, attaches to the
subarticular cartilage of the third interphalangeal joint.
INNERVATION.--The posterior division of the tibial nerve sends a branch
into the posterior edge of the medial head, then passes between the
latter and the medial head of M. flexor perforatus digiti III; as it
extends distally it gives off twigs to the medial surface of the medial
head, to the deep surface of the lateral head, and to the deep surface
of the anterolateral head.
INDIVIDUAL VARIATION.--In one leg, an additional branch arises from the
tibial nerve at the level of origin of the posterior division and enters
the posterior surface of the medial head; a twig from this branch
anastomoses with the first twig of the posterior division to the same
head; a branch of the medial division joins the posterior division
distal to the origin of the twigs to the medial head but proximal to the
origin of the twigs to the other heads.
_T. cupido_
INDIVIDUAL VARIATION.--None of significance.
_P. p. jamesi_
INDIVIDUAL VARIATION.--In four legs, a tiny vinculum connects with the
tendon of M. flexor digitorum longus (which see).
=_M. Flexor Perforatus Digiti III_=, Figs. 13, 14, 15, 16, 17
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Divided into two widely separated
heads--medial and anterolateral--with completely separate bellies but
with common insertional tendon; small _anterolateral head_ on lateral
aspect of thigh deep to M. flexor perforans et perforatus digiti II and
posterior to M. flexor digitorum longus; fleshy part of head
distolateral to belly of M. flexor perforatus digiti IV; fleshy part
fused to lateral edge of belly of M. flexor perforatus digiti II;
proximal part of head a slender ossified tendon fused to anterior edge
of both fleshy and tendinous parts of anterolateral head of M. flexor
perforatus digiti IV and to lateral edge of anterolateral head of M.
flexor perforatus digiti II; this tendon passing deep to tendon of
insertion of M. extensor iliofibularis and to peroneal nerve; large
_medial head_ on posteromedial surface of thigh anterior to medial edge
of M. gastrocnemius pars externa, lateral to M. gastrocnemius pars
media, and medial to M. flexor perforatus digiti IV; fused to medial
surface of medial head of latter and to medial edges of Mm. flexor
perforatus digiti II and flexor hallucis longus; proximal end of head
tendinous.
ORIGIN.--The _medial head_ attaches tendinously to the medial part of
the popliteal area in common with the medial head of M. flexor
perforatus digiti II and with the medial edges of Mm. flexor perforatus
digiti IV (medial head) and flexor hallucis longus; and is also fused to
the articular capsule. The _anterolateral head_ arises in common with
the anterolateral heads of Mm. flexor perforatus digiti II and flexor
perforatus digiti IV (see account of latter).
INSERTION.--The short unossified tendon of the anterolateral head and
the longer ossified tendon of the medial head join (after the latter
becomes flexible) a short distance above the tibial cartilage, forming a
broad flat common tendon that passes posterior to the tibial cartilage
(in a shallow groove of the latter); the main part of the tendon is deep
to the tendons of Mm. flexor perforatus digiti IV and flexor perforans
et perforatus digiti III, but forms separate thin sheaths around these
two tendons at the level of the tibial cartilage. A thin sheet of
connective tissue covers these three tendons and attaches by its edges
to the tibial cartilage, forming a sheath for them. These three tendons
pass through the superficial groove in the hypotarsus deep to the tendon
of M. gastrocnemius; the tendon of M. flexor perforatus digiti III is
ossified for most of the length of the tarsometatarsus; a short distance
below the hypotarsus, the anterior branch of the tendon of M. peroneus
longus attaches broadly to the lateral edge of the tendon of M. flexor
perforatus digiti III. In the proximal part of the tarsometatarsus the
tendon is deep to the tendon of M. flexor perforans et perforatus digiti
III, but farther distally becomes medial and then superficial to the
latter and lateral to the tendon of M. flexor perforans et perforatus
digiti II; near the distal end of the tarsometatarsus a narrow but
strong vinculum extends from the lateral edge of the tendon somewhat
distally to the lateral edge of the tendon of M. flexor perforans et
perforatus digiti III. At the distal end of the tarsometatarsus the
tendon expands before entering the ventral surface of digit III where it
soon divides into two branches, between which emerge the tendons of Mm.
flexor perforans et perforatus digiti III and flexor digitorum longus;
the lateral branch attaches to the subarticular cartilage ventral to the
first interphalangeal joint and to the lateral surface of the distal end
of the first phalanx; the medial branch has similar attachments on the
medial side of the digit.
INNERVATION.--The posterior division of the tibial nerve passes between
the medial heads of M. flexor perforatus digiti III and M. flexor
perforatus digiti IV and sends a twig to the lateral surface of the
former, then passes deep to the common belly of M. flexor perforatus
digiti IV and sends a twig to the posterior surface of the anterolateral
head of M. flexor perforatus digiti III.
INDIVIDUAL VARIATION.--None of significance.
_T. cupido_
INDIVIDUAL VARIATION.--In one leg, an extra branch (immediately distal
to the branch to M. gastrocnemius pars media) of the medial division of
the tibial nerve penetrates the medial surface of the proximal end of
the medial head.
_P. p. jamesi_
INDIVIDUAL VARIATION.--None of significance.
=_M. Flexor Perforatus Digiti II_=, Figs. 15, 17
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Bipinnate; on posterior aspect of
shank deep to M. flexor perforatus digiti IV and between two heads of M.
flexor perforatus digiti III; bounded anteriorly by Mm. flexor digitorum
longus and flexor hallucis longus; proximal part divided into three
small heads--medial, lateral, and anterolateral; medial and proximal
parts of _medial head_ tendinous and extremely thin except for ossified
medial edge; proximal part of _lateral head_ tendinous and lateral to
insertional tendon of M. extensor iliofibularis; both tendinous and
fleshy parts fused to overlying tendon of M. flexor perforatus digiti
IV; narrow _anterolateral head_ fused to overlying anterolateral head of
latter muscle and (anterolateral edge) to ossified tendon of
anterolateral head of M. flexor perforatus digiti III; lateral edge of
common belly fused to latter head; medial edge of muscle fused to medial
heads of Mm. flexor perforatus digiti IV and flexor perforatus digiti
III and to M. flexor hallucis longus.
ORIGIN.--The _medial head_ attaches by a slender ossified tendon to the
medial part of the popliteal area in common with the medial head of M.
flexor perforatus digiti III and with the medial edges of Mm. flexor
perforatus digiti IV (medial head) and flexor hallucis longus; this
head is also fused to the articular capsule. The above-mentioned
ossified part of the tendon is situated at the junction of M. flexor
perforatus digiti II and M. flexor perforatus digiti III (medial head)
and could be considered to be a part of the latter rather than the
former. The flat tendon of the _lateral head_ arises in common with the
lateral head of M. flexor perforatus digiti IV (which see). The
_anterolateral head_ arises in common with the anterolateral heads of
Mm. flexor perforatus digiti IV and flexor perforatus digiti III (see
former).
INSERTION.--The short, slender, ossified tendon becomes flexible and
passes through the canal in the tibial cartilage that lies medial to the
canal for M. flexor hallucis longus and lateral to the canals for Mm.
flexor digitorum longus and flexor perforans et perforatus digiti II.
The tendon passes with the tendon of M. flexor perforans et perforatus
digiti II (lateral to latter) through the canal in the hypotarsus that
is deep to the groove for M. flexor perforatus digiti III and
superficial to the canal for M. flexor digitorum longus; the former
canal has a bony floor and sides but a fibrous roof; a fibrous partition
subdivides the proximal half of this canal, forming a separate channel
for each tendon. The tendon is ossified for most of the length of the
tarsometatarsus and is situated lateral (adjacent) to the posterior
metatarsal crest; immediately below the hypotarsus, the tendon becomes
situated deep to the tendon of M. flexor perforans et perforatus digiti
II and farther distally becomes situated medial and finally superficial
to the latter; at the distal end of the tarsometatarsus the tendon
expands greatly and its edges (thick) pass dorsally around the
underlying flexor tendons and become continuous with the subarticular
cartilage ventral to the trochlea for digit II. The tendon extends onto
the ventral surface of digit II and attaches by its edges to the
ventromedial and ventrolateral surfaces of the proximal part of the
first phalanx (the lateral edge extending farthest distally); the
tendons of Mm. flexor perforans et perforatus digiti II and flexor
digitorum longus emerge from the distal end of the tendon of M. flexor
perforatus digiti II.
INNERVATION.--The posterior division of the tibial nerve passes between
the medial heads of Mm. flexor perforatus digiti III and flexor
perforatus digiti IV and gives a twig to the superficial surface of each
of the three heads of M. flexor perforatus digiti II and sometimes gives
another twig to the superficial surface of the distal part of the common
belly.
INDIVIDUAL VARIATION.--In one leg, a vinculum connects the tendon with
that of M. flexor perforans et perforatus digiti II (which see).
_T. cupido_
INDIVIDUAL VARIATION.--The canal in the hypotarsus through which the
tendon passes has a bony (instead of fibrous) roof in one leg.
_P. p. jamesi_
INDIVIDUAL VARIATION.--The variation given above for _T. cupido_ is
found in both legs of one specimen.
=_M. Flexor Hallucis Longus_=, Figs. 15, 19A
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on posterior
aspect of shank deep to M. flexor perforatus digiti II and to proximal
end of medial head of M. flexor perforatus digiti IV; bounded
anterolaterally by M. flexor digitorum longus and anteromedially by M.
plantaris; tendinous anteromedial surface of proximal end fused to
common tendon of origin of medial heads of Mm. flexor perforatus digiti
III and flexor perforatus digiti II; belly ending approximately halfway
down shank.
ORIGIN.--The origin is fleshy and tendinous (anteromedial surface) from
the popliteal area immediately distal to the origin of the medial head
of M. flexor perforatus digiti IV, extending laterally to the area
immediately proximal to the external femoral condyle (medial to the
origin of M. gastrocnemius pars externa); the muscle also arises from
the proximal end of the posterior part of the articular capsule.
INSERTION.--The slender ossified tendon becomes flexible and passes
through the canal in the tibial cartilage that lies lateral to the canal
for M. flexor perforatus digiti II, then passes through a slight groove
in the lateral surface of the hypotarsus and becomes ossified again;
midway of the tarsometatarsus, the tendon becomes superficial to the
tendon of M. flexor digitorum longus and is connected with the latter by
an extensive vinculum, which extends from the deep surface and lateral
edge of the tendon of M. flexor hallucis longus distally to the
superficial surface of the tendon of M. flexor digitorum longus; the
tendon continues, unossified and considerably reduced in size, distally
medial to the tendon of M. flexor digitorum longus, and passes through
the flexor groove of the first metatarsal anterolateral (adjacent) to
the tendon of M. flexor hallucis brevis, then passes deep to the
terminal expansion of the latter onto the ventral surface of the hallux;
the tendon emerges from under the end of the tendon of M. flexor
hallucis brevis and attaches to the ventral surface of the ungual
phalanx; a weak dorsal slip attaching to the ventral surface of the
distal end of the first phalanx is usually present.
INNERVATION.--A branch of the medial division of the tibial nerve passes
along the medial edge of the muscle, giving several twigs into it.
INDIVIDUAL VARIATION.--None of significance in any of the three species
studied.
=_M. Plantaris_=, Figs. 15, 19A
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on
posteromedial surface of tibiotarsus; bounded medially by M.
gastrocnemius pars interna and tendon of M. flexor cruris medialis,
posteriorly by M. gastrocnemius pars media and medial head of M. flexor
perforatus digiti III, posterolaterally by M. flexor hallucis longus;
medial to M. flexor digitorum longus; anterolateral surface of proximal
end often slightly overlapping and fused to posterior surface of medial
end of M. popliteus; belly terminating above middle of shank.
ORIGIN.--The origin is fleshy and tendinous (distal edge only) from an
elongate area on the posteromedial surface of the proximal end of the
tibiotarsus adjacent to the insertion of M. popliteus.
INSERTION.--The long, slender, ossified tendon extends along the
posteromedial aspect of the tibiotarsus and becomes flexible just before
attaching to the proximomedial part of the tibial cartilage. The tibial
cartilage is a large, mostly cartilaginous pad fitting closely over the
posterior surface of the intratarsal joint; the distomedial corner is
ossified. This cartilage is perforated by the tendons of several flexor
muscles; the distal end of the cartilage attaches to the posteroproximal
corner of the tarsometatarsus.
INNERVATION.--A branch of the medial division of the tibial nerve
penetrates the lateral surface.
INDIVIDUAL VARIATION.--In one leg, a small bundle of fibers separates
from the proximal end of the muscle, forming a short accessory head
which attaches, separately from the remainder, to the articular capsule
posteroproximal to the main origin; a blood vessel passes between the
main and accessory heads.
_T. cupido_
INDIVIDUAL VARIATION.--In one leg, a small bundle of fibers arises from
the medial collateral ligament. In another leg, the nerve to M.
gastrocnemius pars interna passes through a gap in the origin of M.
plantaris rather than distal to its origin.
_P. p. jamesi_
INDIVIDUAL VARIATION.--The nerve branch supplying M. gastrocnemius pars
interna gives a minute twig to the deep surface of the free belly of M.
plantaris in one instance.
=_M. Flexor Digitorum Longus_=, Figs. 14, 16, 17, 19A
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Relatively broad; bipinnate; on
posterolateral surface of tibiotarsus; bounded posteromedially by M.
flexor hallucis longus, posteriorly by M. flexor perforatus digiti II
and anterolateral head of M. flexor perforatus digiti III, laterally by
Mm. flexor perforans et perforatus digiti III and flexor perforans et
perforatus digiti II, and anterolaterally by Mm. peroneus brevis and
tibialis anticus; anterior surface of lateral part of distal half of
common belly fused to M. peroneus brevis; divided into three
heads--posterior (largest), lateral, and medial; _posterior head_ on
posterior surface of head of fibula; overlapping and fused to lateral
end of M. popliteus; proximomedial corner deep to latter; _lateral head_
on lateral surface of fibula; lateral and posterior heads separated by
insertion of M. extensor iliofibularis; these two heads joined
immediately distal to insertion of latter; _medial head_ on posterior
surface of tibiotarsus; group of blood vessels and nerves passing
between medial and posterior heads; these two heads joined several mm.
distal to junction of lateral and posterior heads; deep surface of
insertional tendon near distal end of tarsometatarsus serving as origin
for M. lumbricalis.
ORIGIN.--_Posterior head_: This arises fleshily from the posterior
surface of the fibula beginning almost at the proximal end and from the
medial surface of the fibula beginning deep to the distal part of M.
popliteus. _Lateral head_: This arises fleshily (sometimes partly
tendinously) from the lateral surface of the fibula proximal to the
fibular tubercle. Some fibers arise from the distal edge of the tendon
of insertion of M. extensor iliofibularis. _Medial head_: This arises
fleshily from the posterior surface of the tibiotarsus just medial to
the distal part of the posterior head, distal to M. popliteus, and
either lateral or distolateral to the origin of M. plantaris. Distal to
the junction of the three heads, the muscle arises fleshily from the
posterior surface of the tibiotarsus (except the distal part) and from
the medial and posterior surfaces of the fibula.
INSERTION.--The slender ossified tendon becomes flexible and passes
through the canal in the tibial cartilage that lies anterolateral to the
canal for M. flexor perforans et perforatus digiti II and anteromedial
to the canal for M. flexor perforatus digiti II, then passes through the
bony canal of the hypotarsus that is deep to all the other flexor
tendons; the tendon ossifies again and lies adjacent (lateral) to the
posterior metatarsal crest; the vinculum from the tendon of M. flexor
hallucis longus fuses extensively to the superficial surface of the
present tendon a short distance below the midpoint of the
tarsometatarsus; the tendon is considerably broader below this point
than above it. At the level of the first metatarsal, the tendon divides
into three branches (unossified) that diverge, each passing through a
groove on the ventral surface of the subarticular cartilages ventral to
the trochleae, then pass onto the ventral surfaces of digits II, III,
and IV. On _digit IV_ the tendon gives off two dorsal fibro-elastic
slips before attaching to the ventral surface of the ungual phalanx; one
slip attaches to the subarticular cartilage ventral to the third
interphalangeal joint, the other to the subarticular cartilage of the
fourth joint and may also attach in part to the distal end of the fourth
phalanx. On _digit III_ the tendon gives off two dorsal slips before
attaching to the ventral surface of the ungual phalanx; one slip
attaches to the subarticular cartilage of the second interphalangeal
joint, the other to the subarticular cartilage of the third joint and
may also attach in part to the distal end of the third phalanx. On
_digit II_ the tendon gives off one dorsal slip before attaching to the
ventral surface of the ungual phalanx; the slip attaches to the
subarticular cartilage of the second interphalangeal joint and may also
attach in part to the distal end of the second phalanx.
INNERVATION.--A branch of the medial division of the tibial nerve
penetrates the medial surface of the posterior head.
INDIVIDUAL VARIATION.--In half the legs, the proximal end of the lateral
head is notched for the passage of the peroneal nerve; the main part of
the head lies medial to this nerve; the short fleshy slip lateral to
this nerve arises by a long, slender, and extremely weak tendon from
connective tissue surrounding the femorotibiotarsal joint. In one leg, a
bundle of fibers separates from the lateral head and attaches to the
terminal four mm. of the anterior (proximal) edge of the tendon of M.
extensor iliofibularis. Each of the following variations occurs in
several legs: a third dorsal slip on digit IV attaches to the distal end
of the fourth phalanx in some legs and to the subarticular cartilage of
the fourth joint in other legs; a third dorsal slip on digit III
attaches to the distal end of the third phalanx in some legs and to the
subarticular cartilage of the third joint in other legs; a second dorsal
slip on digit II attaches to the distal end of the second phalanx in
some legs and to the subarticular cartilage of the second joint in other
legs.
_T. cupido_
INDIVIDUAL VARIATION.--The dorsal slips of insertion show variations
similar to those noted above for _T. pallidicinctus_.
_P. p. jamesi_