entire obturator internus of Berger (1952). Pars dorsalis is apparently
equivalent to the dorsal part of Berger's obturator externus. The
ventral part of the obturator externus of Berger represents the fused
pars antica and pars ventralis.
The main parts of the obturator muscle appear to be pars postica and
pars antica. Pars dorsalis and pars ventralis are more variable; in
_Coccyzus_ these two parts are closely associated with pars antica
whereas in _Tympanuchus_ they are most closely associated with pars
postica. Apparently pars dorsalis and pars ventralis may be absent in
some birds.
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Deeply situated immediately
posterior to head of femur; part extending through obturator foramen and
lying inside pelvis; extrapelvic part deep to Mm. flexor ischiofemoralis
and piriformis; muscle partially divisible into four parts--pars antica,
pars dorsalis, pars ventralis, and pars postica (fig. 20K); _pars
postica_: mostly inside pelvis; much larger than other parts; broad
(narrow anteriorly); on medial surface of ischium; composed of several
fascicles; anterior end forming narrow, heavy tendon (with some fleshy
fibers on posterior part of deep surface) passing through obturator
foramen; anteriormost fleshy fibers of ventralmost fascicle fused with
pars ventralis; _pars ventralis_: essentially extrapelvic (see origin);
mostly ventral to tendon of pars postica; superficial to pars antica;
fused to anterior fleshy part of pars postica; anterodorsal edge usually
adjacent to, and often slightly fused with, ventral edge of pars
dorsalis (deep to tendon of pars postica); _pars dorsalis_: entirely
extrapelvic; mostly dorsal to tendon of pars postica; superficial to
dorsal part of pars antica; _pars antica_: extremely short but
relatively thick; entirely fleshy; entirely extrapelvic; between
obturator foramen and head of femur; anterior surface adjacent to
articular capsule; almost completely covered by other parts of muscle;
proximal end of posterior surface often slightly fused with adjacent
parts of pars ventralis and pars dorsalis.
ORIGIN.--_Pars postica_: This arises fleshily from the medial surface of
the entire ischium except the posterior end, from the dorsomedial and
medial surfaces of the anterior half of the pubis as far forward as the
obturator foramen, from the internal ilio-ischiatic crest, from the
medial surface of the ilium for a short distance posterior to this
crest, and from the iliac recess; the posteroventral corner usually
arises from the medial surface of the ischiopubic membrane. _Pars
ventralis_: This arises fleshily from the dorsomedial edge of the
ventral border of the obturator foramen (fig. 20M) and (narrowly) from
the anterior border of the foramen; this part may or may not arise from
the lateral surface of the anteroventral border of the foramen and is
usually adjacent along the anterior border of the foramen to pars
dorsalis; _pars ventralis_ is continuous along the ventral border of the
foramen with the intrapelvic origin of pars postica. _Pars dorsalis_:
This arises fleshily from the lateral surface of the anterodorsal border
of the foramen (fig. 20L) and may extend posteriorly along the dorsal
border of the foramen. _Pars antica_: This arises fleshily from the
depresssed area anterior to the obturator foramen (adjacent to pars
dorsalis and pars ventralis); the posteroventral corner may arise from
the lateral surface of the anteroventral border of the obturator foramen
(ventral to the anterior end of pars ventralis; fig. 20L).
INSERTION.--_Pars postica_: Several tendinous bands (intrapelvic)
converge and coalesce, forming a single strong tendon that passes
through the obturator foramen and attaches to the lateral surface of the
femoral trochanter a short distance posterior to the insertion of M.
gluteus profundus and proximal to the insertion of M. flexor
ischiofemoralis. _Pars ventralis_: The attachment is fleshy and
tendinous to the ventral edge and the deep surface of the tendon of pars
postica. _Pars dorsalis_: The attachment is fleshy and tendinous to the
dorsal edge of the tendon of pars postica. _Pars antica_: The attachment
is fleshy to the posterior surface of the proximal end of the femur
several mm. posterior to the insertion of pars postica; the lateral edge
attaches to the obturator ridge.
INNERVATION.--The muscle is supplied by the obturator nerve; several
twigs, which do not pass through the obturator foramen, penetrate the
anterior part of the medial surface of pars postica; several twigs pass
through the obturator foramen and supply pars dorsalis, pars ventralis,
and pars antica.
INDIVIDUAL VARIATION.--In some cases the origin of pars postica does not
include the dorsal end of the internal ilio-ischiatic crest nor the
ilium posterior to it. Tiny but distinct accessory slips are sometimes
present. In one leg a tendinous slip of pars antica extends beyond the
remainder of the muscle and inserts independently on the trochanter
close to the insertion of pars postica. In another leg, a fleshy and
tendinous slip of pars antica attaches to the deep surface of the
insertional tendon of pars postica. In still another leg, a fleshy and
tendinous slip of pars dorsalis inserts adjacent (anterior) to the
dorsal edge of the insertion of pars antica.
_T. cupido_
INDIVIDUAL VARIATION.--The variations are similar to those given above
for _T. pallidicinctus_ except that there is no slip of pars antica
attaching to the tendon of pars postica.
_P. p. jamesi._
INDIVIDUAL VARIATION.--There are variations similar to those given above
for _T. pallidicinctus_ except that there is no independent slip of pars
antica attaching on the trochanter close to the insertion of pars
postica. Pars dorsalis may be quite small. In several legs, pars
dorsalis is more closely associated with pars antica than with pars
postica; in one of these, pars dorsalis is indistinguishably fused with
pars antica (inserting with the latter) except for a few fibers which
insert with pars postica.
=_M. Femorocruralis_= (M. accessorius semitendinosi), Figs. 14, 15, 16,
17
Fisher (Fisher, 1946; Fisher and Goodman, 1955) considers this muscle as
an accessory head of M. flexor cruris lateralis. The reasons for this
change in terminology are given in the section on terminology.
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Short and broad; posterior to distal
part of femur; deep to Mm. extensor iliofibularis and vastus lateralis
pars postica; bounded posteriorly by M. flexor cruris lateralis,
medially by Mm. adductor superficialis and adductor profundus, and
distally by M. gastrocnemius pars media; fused to a variable degree with
the latter (in some cases these two muscles fused firmly together,
appearing as single muscle); distal and medial to proximal end of M.
flexor perforatus digiti IV.
ORIGIN.--The muscle arises fleshily (thin proximally, thick distally)
from the posterior surface of approximately the distal half of the femur
between the posterior and posterolateral intermuscular lines. The
ventral end is continuous with the origin of M. gastrocnemius pars
media, adjacent (medial) to the origin of M. vastus lateralis pars
postica, and adjacent (lateral) to the insertions of Mm. adductor
superficialis and adductor profundus.
INSERTION.--The attachment is to the tendinous raphe in common with M.
flexor cruris lateralis (which see).
INNERVATION.--One or two tiny branches come off the tibial nerve near
the distal end of the main trunk of the sciatic nerve, pass anteriorly
deep to the peroneal nerve, and penetrate the lateral surface.
INDIVIDUAL VARIATION.--In two legs, the branch of the medial division of
the tibial nerve which supplies M. gastrocnemius pars media sends a twig
to the lateral surface of the distal end of M. femorocruralis (in
addition to the usual innervation).
_T. cupido_
INDIVIDUAL VARIATION.--None of significance.
_P. p. jamesi_
DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The muscle is much wider,
extending farther proximally on the femur.
INDIVIDUAL VARIATION.--None of significance.
=_M. Gastrocnemius_=, Figs. 12, 13, 15
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Divided into three distinct, widely
separated parts--pars externa, pars interna, and pars media; _pars
externa_: large; on posterolateral surface of shank; narrow proximally
and distally; bounded anterolaterally by M. flexor perforans et
perforatus digiti II and anteromedially by medial head of M. flexor
perforatus digiti III; completely separate from pars interna and media
except for common tendon of insertion; _pars interna_: large; on
anteromedial surface of shank; narrow distally; bounded anterolaterally
by M. peroneus longus and posteromedially by pars media (proximally) and
medial head of M. flexor perforatus digiti III; broad sheet of tough
connective tissue extending between distal parts of pars externa and
pars interna; covering underlying M. flexor perforatus digiti III
(medial head), somewhat fused with anteroproximal edge of M. peroneus
longus; _pars media_: small and short; on medial surface of proximal
part of shank; deep to tendon of insertion of M. flexor cruris medialis;
bounded anteromedially by pars interna, posterolaterally by medial head
of M. flexor perforatus digiti III, and proximally by M. femorocruralis;
fused to latter, and boundary between the two difficult to locate.
ORIGIN.--_Pars externa_: The short cylindrical tendon fuses with the
anterior half of the distal arm of the tendinous guide loop for M.
extensor iliofibularis and attaches in common with the latter to the
posterolateral surface of the femur immediately proximal to the fibular
condyle; the attachment is proximal (adjacent) to the origin of M.
flexor perforans et perforatus digiti II and distal (adjacent) to the
origin of M. flexor perforatus digiti IV and is fused to the articular
capsule.
_Pars interna_: The proximal end is partly separable into two layers--a
superficial longer one and a deep shorter one. The superficial layer
attaches fleshily to the ventral part of the anterior surface of the
patella and to the medial half of the superficial surface of the
patellar tendon; this layer slightly overlaps the distal fleshy end of
M. extensor iliotibialis anticus. The deep layer (overlapped by the
superficial layer) attaches to the medial surface of the inner cnemial
crest, to the rotular crest medial to the latter, to the medial surface
of the proximal part of the tibiotarsus, and (posteroproximal corner) to
the distomedial edge of the patellar tendon and to the articular capsule
posteromedial to the rotular crest; the entire ventral edge is
tendinous, the remainder fleshy.
_Pars media_: This arises fleshily from an oblique line beginning at the
distal end of the origin of M. femorocruralis (continuous with the
latter) and extending distomedially across the proximal part of the
popliteal area to the proximal edge of the internal condyle, then
attaching to the adjacent part of the articular capsule; this part is
adjacent (distal) to the insertion of M. adductor profundus and adjacent
(proximomedial) to the medial head of M. flexor perforatus digiti IV.
INSERTION.--_Pars media_ narrows distally with a narrow tendon along the
posterior edge of the fleshy belly; approximately one third of the way
down the tibiotarsus the fleshy part terminates and the tendon joins the
posterior edge of pars interna, continuing distally in this position.
The ossified tendon on the superficial surface of the distal part of
_pars interna_, continuous posteriorly with the tendon of pars media, is
joined approximately two thirds of the way down the tibiotarsus by the
tendon of pars externa; the fleshy belly of pars interna ends just below
the junction. The ossified tendon on the superficial surface of the
distal part of _pars externa_ extends beyond the fleshy belly and
becomes flexible before joining the tendon of pars interna and media.
The common tendon (partly ossified) extends along the posterior surface
of the tibiotarsus and widens as it passes posterior to the tibial
cartilage, bound to the latter by a thin tough sheet of connective
tissue which attaches to the edges of the tibial cartilage, thus forming
a sheath for the tendon; the tendon attaches by its edges to the
posterior edges of the calcaneal ridges of the hypotarsus, then
continues distally (much reduced in thickness) along the posterior
surface of the tarsometatarsus, enclosing the flexor tendons; the
lateral edge of the tendon attaches to the posterolateral edge of the
tarsometatarsus, terminating immediately above the level of the hallux;
the medial edge attaches to the edge of the posterior metatarsal crest;
the tendon terminates as a thin sheet that attaches to the fascia on the
sole of the foot. (Hudson, _et al._, 1959 consider the posterior
metatarsal crest to be an ossified part of the tendon of M.
gastrocnemius.)
INNERVATION.--A branch of the lateral division of the tibial nerve
penetrates the proximal part of the medial surface of pars externa. One
or two branches of the medial division of the tibial nerve pass deep to
M. plantaris and penetrate the deep surface of the posterior part of
pars interna. The most proximal branch of the medial division of the
tibial nerve penetrates the lateral surface of pars media.
INDIVIDUAL VARIATION.--None of significance.
_T. cupido_
INDIVIDUAL VARIATION.--In one leg, the lateral edge of pars interna
overlaps the proximomedial edge of M. peroneus longus; some fibers
attach to the lateral surface of the inner cnemial crest.
_P. p. jamesi_
DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The proximal end of pars
interna does not reach the patella.
INDIVIDUAL VARIATION.--In one leg, an additional twig to pars media
arises from the distal branch to M. femorocruralis.
=_M. Flexor Perforans et Perforatus Digiti II_=, Figs. 12, 14
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Long, slender, and Y-shaped; on
lateral surface of shank; the two heads enclosing M. flexor perforans et
perforatus digiti III; _posterior head_ bounded posteriorly by M.
gastrocnemius pars externa; extreme proximal end deep to M. vastus
lateralis pars postica; anterior surface fused to posterior surface of
M. flexor perforans et perforatus digiti III; deep surface fused to
tendinous part of lateral head of M. flexor perforatus digiti IV;
_anterior head_ tendinous except for extreme distal end; covered by, and
fused to, posterior edge of M. peroneus longus; fused to anterior
surface of M. flexor perforans et perforatus digiti III; two heads join
above middle of shank; anteroproximal and posterodistal parts of common
belly usually tendinous.
ORIGIN.--_Anterior head_: This arises by a narrow tendon (partly
ossified) from the distal tip of the outer cnemial crest. The tendon is
so intimately fused with a connective tissue sheet fused to the deep and
posterior surfaces of M. peroneus longus and to the anterior surface of
M. flexor perforans et perforatus digiti III that M. flexor perforans et
perforatus digiti II could be considered to arise from these two
muscles. _Posterior head_: This arises mostly fleshily from the lateral
surface of a compound sheet of tough connective tissue formed by the
fusion of the tendinous posteroproximal corner of M. flexor perforans et
perforatus digiti III, the proximal parts of the tendons of origin of
the lateral heads of Mm. flexor perforatus digiti IV and flexor
perforatus digiti II, the fibular and distal arms of the guide loop for
M. extensor iliofibularis, and the lateral part of the articular
capsule; a part of the common tendon of origin of the anterolateral
heads of Mm. flexor perforatus digiti III, flexor perforatus digiti IV,
and flexor perforatus digiti II also contributes to this sheet, which
attaches to the lateral surface of the external condyle of the femur and
to the anterolateral surface of the head of the fibula; for convenience
in description, this complex connective tissue sheet will hereafter be
termed the _femorofibular fascia_. The anteroproximal corner of the
posterior head of M. flexor perforans et perforatus digiti II often
attaches to the lateral surface of the vinculum that passes from the
femorofibular fascia to the deep surface of the patellar tendon; the
extreme proximal end usually attaches fleshily to a small area on the
femur immediately proximal to the fibular condyle and adjacent (distal)
to the attachment of the distal arm of the guide loop for M. extensor
iliofibularis.
INSERTION.--The common belly terminates approximately two thirds of the
way down the shank; the slender ossified tendon begins along the
posteromedial edge of the common belly, continues distally along the
posterior surface of the shank, and becomes flexible before passing
through the canal in the tibial cartilage that lies posteromedial to the
canal for M. flexor digitorum longus. The tendon passes with the tendon
of M. flexor perforatus digiti II (medial to the latter) through a canal
in the hypotarsus (see M. flexor perforatus digiti II); just below the
hypotarsus, the tendon becomes superficial to the tendon of M. flexor
perforatus digiti II and farther distally becomes lateral and finally
deep to the latter; the tendon is ossified for most of the length of the
tarsometatarsus. At the distal end of this bone, the tendon expands
before passing onto the ventral surface of digit II between the tendons
of Mm. flexor perforatus digiti II and flexor digitorum longus; at the
level of the first phalanx, the edges of the tendon extend dorsally
around the tendon of M. flexor digitorum longus and fuse, forming a
sheath around the latter; the latter emerges from the sheath near the
distal end of the first phalanx; the tendon attaches to the proximal end
of the subarticular cartilage ventral to the first interphalangeal joint
(the strongest attachment is on the medial side).
INNERVATION.--The lateral division of the tibial nerve sends twigs into
the posteromedial edge of the posterior head.
INDIVIDUAL VARIATION.--In one leg, the fleshy part of the anterior head
is unusually long. In another leg, the anterior head is entirely
tendinous. In one leg, a bundle of fibers of the posterior head attaches
to the deep surface of the distal part of the patellar tendon. In one
leg, near the middle of the tarsometatarsus a rather long and narrow but
thick and strong vinculum arises from the tendon of M. flexor perforatus
digiti II and, farther distally, joins the tendon of M. flexor perforans
et perforatus digiti II.
_T. cupido_
INDIVIDUAL VARIATION.--In one leg, the posterior head arises in part
from the distolateral edge of the patellar tendon and in another, in
part from the superficial surface of the distolateral corner of the
patellar tendon.
_P. p. jamesi_
INDIVIDUAL VARIATION.--None of significance.
=_M. Flexor Perforans et Perforatus Digiti III_=, Figs. 12, 14
_T. pallidicinctus_
GENERAL DESCRIPTION AND RELATIONS.--Thick, bipinnate; on lateral surface
of proximal part of shank between two heads of M. flexor perforans et
perforatus digiti II; bounded anteriorly by M. peroneus longus; anterior
surface fused with tendinous anterior head of M. flexor perforans et
perforatus digiti II; anterolateral edge somewhat fused to posterior
edge of M. peroneus longus superficial to latter tendon; posterior
surface fused to posterior head of M. flexor perforans et perforatus
digiti II; distal part of belly covered by common belly of latter
muscle; posteromedial edge fused to underlying lateral head of M. flexor
perforatus digiti IV; anteromedial edge usually somewhat fused to
underlying M. flexor digitorum longus.
ORIGIN.--The origin is fleshy and tendinous from the edge of the outer
cnemial crest and fleshy from the superficial surface of the
distolateral part of the patellar tendon; the posteroproximal corner
arises tendinously from the femorofibular fascia.
INSERTION.--The belly narrows abruptly, terminating approximately at the
middle of the shank; the slender ossified tendon extends posterodistally
along the shank, becoming flexible before passing posterior to the
tibial cartilage deep to the tendon of M. gastrocnemius, medial to the
tendon of M. flexor perforatus digiti IV, and superficial to the medial
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 perforans et
perforatus digiti II); the tendon is ossified for most of the length of
the tarsometatarsus; at midlength of the latter, the tendon lies between
the tendons of Mm. flexor perforatus digiti IV and flexor perforatus
digiti III; near the distal end of the tarsometatarsus, the tendon
becomes lateral and then deep to the tendon of M. flexor perforatus
digiti III and is connected by a vinculum to the latter (which see). The
tendon enters the ventral surface of digiti III between the tendons of
Mm. flexor perforatus digiti III and flexor digitorum longus; after
sending a dorsal slip (lateral to the tendon of M. flexor digitorum
longus) to the subarticular cartilage ventral to the first
interphalangeal joint, the tendon divides into two branches, between
which emerges the tendon of M. flexor digitorum longus; the lateral
branch attaches to the subarticular cartilage of the second
interphalangeal joint and to the lateral surface of the distal end of
the second phalanx; the medial branch has similar attachments on the
medial side of the digit.
INNERVATION.--A branch of the lateral division of the tibial nerve
passes deep to the posterior head of M. flexor perforans et perforatus
digiti II and enters the posteromedial edge of M. flexor perforans et
perforatus digiti III.
INDIVIDUAL VARIATION.--In both legs of one specimen, the part arising
from the femorofibular fascia appears as a distinct but short accessory
head. There is no significant individual variation in _T. cupido_ or _P.
p. jamesi_.
=_M. Flexor Perforatus Digiti IV_=, Figs. 14, 16
_T. pallidicinctus_