Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse Part 8

GENERAL DESCRIPTION AND RELATIONS.--Most posterior muscle on medial surface of thigh; long and strap-shaped; bounded anteriorly by M.

adductor profundus; posteroproximal corner of latter medial to anteroproximal part of M. flexor cruris medialis; bounded laterally by Mm. caudofemoralis (proximally) and flexor cruris lateralis (distally); anteroproximal corner adjacent to posteroventral corner of M. flexor ischiofemoralis and lateral to extreme posteroproximal corner of M.

adductor superficialis; distal end tendinous, extending into proximal part of shank; bounded medially by M. gastrocnemius pars interna and laterally by Mm. gastrocnemius pars media and plantaris.

ORIGIN.--The muscle arises by a wide flat tendon from a narrow line on the lateral surface of the ischium dorsal to the ventral ischiatic tubercle.

INSERTION.--The wide flat tendon attaches to a narrow line on the medial surface of the proximal part of the tibiotarsus a short distance anterior to the proximal part of M. plantaris and deep to M.

gastrocnemius pars interna; the proximal end attaches immediately anterior to the distal end of the medial collateral ligament. Part of the common tendon of Mm. flexor cruris lateralis and femorocruralis fuses with the lateral surface of the tendon of M. flexor cruris medialis, inserting in common with it.

INNERVATION.--A branch of the middle tibial division of the sciatic nerve pa.s.ses deep to both heads of M. caudofemoralis and enters the anterior part of M. flexor cruris medialis.

INDIVIDUAL VARIATION.--In several legs, the anterior edge of the proximal part fits into a deep longitudinal groove in the posterior edge of the proximal part of M. adductor superficialis; the two muscles fuse slightly at this point.

_T. cupido_

INDIVIDUAL VARIATION.--In two legs, the extreme posterior end of the origin is from the pubis. In two others, the proximal end is separated by a slight gap from M. adductor superficialis. The nerve arises from the posterior (rather than middle) tibial division in one leg.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The origin is wider; the posterior third to half of the origin is fleshy. The entire origin is from a strongly curved line, the middle part of which attaches to the ventral edge of the ischium posterior to the ventral ischiatic tubercle.

The insertion is wider. The insertional tendon attaches posterior (rather than anterior) to the distal end of the medial collateral ligament; the proximal end of the insertion attaches to the articular capsule (fig. 20E). The insertional tendon is shorter; as a result, the common tendon of Mm. flexor cruris lateralis and femorocruralis fuses with the distal end of the fleshy belly (instead of the tendon) of M.

flexor cruris medialis.

INDIVIDUAL VARIATION.--In two thirds of the legs, the proximal part of the insertion is fleshy rather than tendinous. In one leg, the middle part of the insertional tendon splits into two sheets, one attaching anterior to and one attaching posterior to the distal end of the medial collateral ligament. The nerve may arise from the posterior tibial division (two legs), from the middle tibial division (one leg), or as an independent division of the tibial nerve (three legs). In one leg, the nerve perforates the lateral part of M. flexor ischiofemoralis.

=_M. Caudofemoralis_= (M. piriformis), Figs. 12, 13, 14, 15, 16, 20J

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Posterior to proximal part of shaft of femur and deep to M. extensor iliofibularis; posterior part deep to M. flexor cruris lateralis; bounded medially by Mm. flexor ischiofemoralis (dorsally), flexor cruris medialis (posteriorly), and adductor superficialis (anteroventrally); anterior end distal to anterior end of M. flexor ischiofemoralis; two distinct heads--pars iliofemoralis and pars caudifemoralis; _pars iliofemoralis_ dorsal to pars caudifemoralis; posteroventral corner of former overlapped by latter; pars iliofemoralis wider and much shorter than pars caudifemoralis; extreme posterior end of pars iliofemoralis fused to overlying posteroproximal aponeurosis of M. extensor iliotibialis lateralis; small part of ventral edge sometimes fused with underlying tendinous posteroproximal corner of M. flexor cruris medialis; entirely fleshy except for small triangular tendinous area along dorsal margin at point where branch of middle tibial division of sciatic nerve pa.s.ses deep to muscle; _pars caudifemoralis_ long, thin, narrow, and strap-shaped; overlapping posteroventral corner of ischium; posterior end of fleshy belly narrowed and forming long slender tendon pa.s.sing into caudal musculature; anterior end forming short narrow tendon fused to deep surface of ventral edge of pars iliofemoralis relatively near insertion; tendon continuous to insertion; fleshy anterodorsal corner of pars caudifemoralis slightly overlapped by ventral edge of pars iliofemoralis; some form of connection usually present between anterior part of M. caudofemoralis pars caudifemoralis and dorsal end of raphe between Mm. flexor cruris lateralis and femorocruralis, most often consisting of narrow weak tendon.

ORIGIN.--_Pars iliofemoralis_: This arises fleshily from the ventromedial surface of the posterior part of the lateral iliac process, from the entire lateral ischiatic ridge, and from the lateral surface of the ischium anterior to this ridge nearly as far forward as the posterior edge of origin of M. flexor ischiofemoralis; the posteroventral corner reaches the ventral edge of the ischium and usually attaches to the ischiopubic membrane posterior to M. flexor cruris medialis. _Pars caudifemoralis_: This arises by a narrow tendon from the ventral surface of a broad, thick, tendinous sheet ventral to the pygostyle, which, in turn, attaches to the ventral surface of the pygostyle.

INSERTION.--The common belly formed by the union of the two heads narrows (width variable) and attaches to the posterolateral surface of the femur distal to the level of insertion of M. iliacus and in contact with the posterior edge of origin of M. vastus lateralis pars lateralis; the dorsal part is fleshy and the ventral part is tendinous.

INNERVATION.--A branch of the middle tibial division of the sciatic nerve gives several twigs to the deep surface of pars iliofemoralis; another twig enters the substance of pars iliofemoralis and emerges from the ventral edge of the latter, then enters the dorsal edge of pars caudifemoralis. The latter twig was not found in all legs, but was probably destroyed during dissection.

INDIVIDUAL VARIATION.--The tendinous area in the dorsal margin of pars iliofemoralis is lacking in one leg and extremely small in some others.

In both legs of one specimen, the connection between M. caudofemoralis pars caudifemoralis and the raphe between Mm. flexor cruris lateralis and femorocruralis consists of a small (11 2 mm.) but well developed and entirely fleshy muscle slip (fig. 16). In one leg, the ventral third of this connection is fleshy, the remainder tendinous; in another, this connection is completely lacking.

_T. cupido_

INDIVIDUAL VARIATION.--The tendinous area in the dorsal margin of pars iliofemoralis is lacking in one leg. The connection between pars caudifemoralis and the raphe between Mm. flexor cruris lateralis and femorocruralis is lacking in several legs. A conspicuous variation occurring in three legs is the presence of a tendinous area in the belly of pars caudifemoralis, dividing the latter into proximal and distal parts (fig. 20J). In one leg, the posteroventral corner of pars iliofemoralis arises from the pubis. The origin of pars caudifemoralis in three legs is directly from the anteroventral surface of the pygostyle. In one instance, the insertional tendon of pars caudifemoralis is long and extremely slender and extends for some distance in a groove on the medial surface of pars iliofemoralis before fusing with the latter.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--There is no connection at all between pars caudifemoralis and the raphe between Mm. flexor cruris lateralis and femorocruralis. The posteroventral corner of pars iliofemoralis is some distance dorsal to the ventral edge of the ischium and, therefore, does not attach to the ischiopubic membrane.

INDIVIDUAL VARIATION.--The insertion (narrow) is entirely tendinous in one leg.

=_M. Flexor Ischiofemoralis_= (M. ischiofemoralis), Figs. 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick; on lateral surface of anterior part of ischium; posterior end in lateral iliac fossa; deep to Mm. extensor iliofibularis and caudofemoralis pars iliofemoralis; overlapping ventral extrapelvic part of M. obturator and anteroproximal part of M. adductor superficialis (slightly fused to proximal edge of latter); posteroventral corner contacting anteroproximal corner of M.

flexor cruris medialis; extreme anterodorsal corner usually overlapped by tendon of M. piriformis.

ORIGIN.--The muscle arises fleshily from a large area on the lateral surface of the ischium extending ventrally to the origin of M. adductor superficialis, anteriorly to the level of the posterior end of the obturator foramen, dorsally to the ventral border of the ilio-ischiatic fenestra and to the depth of the lateral iliac fossa, and posteriorly approximately to the level of the ventral ischiatic tubercle.

INSERTION.--The short flat tendon attaches to the lateral surface of the femur immediately posterior to the insertion of M. piriformis.

INNERVATION.--The posterior tibial division of the sciatic nerve penetrates the dorsal surface.

INDIVIDUAL VARIATION.--The ventral part of the insertion may be fleshy.

_T. cupido_

INDIVIDUAL VARIATION.--None of significance.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In all the legs except one, an additional twig arises from the branch to M. flexor cruris medialis and penetrates the lateral surface of M. flexor ischiofemoralis. The ventral part of the insertion is fleshy in one leg.

=_M. Adductor Superficialis_= (M. adductor longus et brevis, pars externa), Figs. 14, 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Posterior to femur, lateral to M.

adductor profundus, and medial to Mm. flexor ischiofemoralis, caudofemoralis, and femorocruralis; proximal end (fleshy) fused to proximal tendinous end of M. adductor profundus.

ORIGIN.--The origin is fleshy and tendinous from the proximal end of the lateral surface of M. adductor profundus and from a narrow line on the ischium adjacent (dorsal) to the origin of the latter; the posterior part of the origin sometimes extends farther dorsally on the lateral surface of the ischium; the origin does not extend so far anteriorly nor so far posteriorly as the origin of M. adductor profundus; the anterior edge is at the posterior border of the obturator foramen.

INSERTION.--The attachment is fleshy and thick (distal end thin) to the posterior surface of the middle part of the femur between the posterior and posterolateral intermuscular lines; the attachment is adjacent (lateral) to the insertion of M. adductor profundus and adjacent (medial) to the origins of Mm. vastus lateralis (proximally) and femorocruralis (distally); the proximal edge is approximately at the level of the distal edge of the insertion of M. caudofemoralis.

INNERVATION.--A branch of the obturator nerve emerges from the obturator foramen dorsal to the tendon of insertion of M. obturator pars postica, turns ventrally (crossing latter), and pa.s.ses deep to the anteroproximal corner of M. adductor superficialis, extending posterodistally between the adductor muscles and giving twigs to the medial surface of M.

adductor superficialis and to the lateral surface of M. adductor profundus.

INDIVIDUAL VARIATION.--The anterior edges of the two adductor muscles are so firmly fused together in some cases that the boundaries cannot be identified at this point. In several legs, there is a deep longitudinal groove in the posterior edge of the proximal part of the muscle into which the anterior edge of M. flexor cruris medialis fits.

_T. cupido_

INDIVIDUAL VARIATION.--In some cases, the anterior edges of the two adductor muscles are firmly fused together.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL T. PALLIDICINCTUS.--The origin is narrower.