Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse Part 5

E. Medial view of distal end of M. flexor cruris medialis of _P. p.

jamesi_ 4L. 1. Part of insertion is covered by medial collateral ligament.

F,G. Lateral views of posteroproximal corner of M. extensor iliotibialis lateralis (removed from specimen). 1. F. _T. pallidicinctus_ 2L. G.

_P. p. jamesi_ 3L.

H,I. Dorsolateral views of M. piriformis. 1. H. _P. p. jamesi_ 1L. I.

_T. cupido att.w.a.teri_ 1L.

J. Lateral view of M. caudofemoralis pars caudifemoralis (removed from specimen) of _T. c. pinnatus_ 4L. 1.

K. Lateral view of extrapelvic part of M. obturator of _T.

pallidicinctus_ 3L (bones not shown). 2.

L,M. Region surrounding obturator foramen of _T. pallidicinctus_ 3L, showing points of attachment of three parts of M. obturator (muscles removed). 3. L. Lateral view. M. Medial view.

N. Anterior view of left tarsometatarsus of _P. p. jamesi_ 4L, showing dorsal intrinsic muscles of foot. 1-1/2. Tendon of M. extensor digitorum longus has been removed.

=_M. Ambiens_=, Figs. 13, 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thin and elongate; on medial surface of thigh; broadest above middle of belly; belly narrowed distally, forming long slender tendon pa.s.sing lateral to distal part of M.

extensor iliotibialis anticus; bounded anterolaterally by M. vastus medialis and posterolaterally by Mm. femoritibialis internus and psoas (proximally).

ORIGIN.--The muscle arises by a short flat tendon from the pectineal process.

INSERTION.--The long slender tendon enters an elongate channel within the patellar tendon; the point of entrance is at the proximal end of the latter tendon just medial to the patella; the tendon pa.s.ses distolaterally (within the channel) below the patella and emerges from the distolateral edge of the patellar tendon and then extends distally along the anterolateral surface of the head of the fibula, superficial to the fibular arm of the guide loop for M. extensor iliofibularis, and joins the anterolateral surface 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; the point of junction is usually immediately proximal to the proximal end of the lateral head of M. flexor digitorum longus.

INNERVATION.--The branch of the middle division of the femoral nerve that supplies M. femoritibialis internus gives off a tiny twig or twigs that penetrate the lateral surface of the proximal part of M. ambiens.

INDIVIDUAL VARIATION.--None of significance in _T. pallidicinctus_ or in _P. p. jamesi_; in _T. cupido_ the origin is partly fleshy in one leg.

=_M. Vastus Lateralis_= (M. femoritibialis externus + part of M.

femoritibialis medius), Figs. 14, 16

Fisher and Goodman (1955) apply the name femoritibialis externus to the muscle unit that I here term the pars postica of M. vastus lateralis.

The reasons for this change are discussed in the section on terminology.

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick; on lateral surface of femur deep to M. extensor iliotibialis lateralis; anterior to M. extensor iliofibularis and lateral to M. vastus medialis; much of lateral surface, except proximal part, fused with overlying M. extensor iliotibialis lateralis; deep surface of anterior half fused with M.

vastus medialis; proximal part overlapping, but usually not fusing with, insertions of Mm. iliacus and caudofemoralis; partially separable into two parts--pars lateralis and pars postica, former const.i.tuting main part of muscle; latter considerably smaller and situated deep to posterodistal part of pars lateralis, except for posterodistal part extending posterior to edge of pars lateralis; proximal part of pars postica strongly fused with pars lateralis; posterodistal tendinous edge of pars lateralis fused or not fused with lateral surface of pars postica; proximal end (narrow) of pars postica tendinous and variable in length.

ORIGIN.--_Pars lateralis_: This arises fleshily from most of the lateral surface and (distally) from the anterior surface of the femur, extending anteriorly to the anterior intermuscular line, fusing with M. vastus medialis, and extending posteriorly to the posterolateral intermuscular line (proximally) and the origin of pars postica (distally); the proximal end begins at the level of the distal edge of the insertion of M. iliotrochantericus medius, contacting the insertions of Mm.

iliotrochantericus medius, piriformis, and flexor ischiofemoralis, and terminates distally at the level of the proximal ends of the femoral condyles.

_Pars postica_: This arises fleshily and tendinously (proximal end and deep surface) from the posterolateral surface of approximately the distal half of the femur, extends posteromedially to the posterolateral intermuscular line where it contacts the origin of M. femorocruralis, and extends anteriorly to the level of a line drawn diagonally across the femur from the proximal end of the origin (at the posterolateral intermuscular line) to the proximal end of the external condyle; the distal end is anterior (adjacent) to the attachment of the proximal arm of the tendinous guide loop for M. extensor iliofibularis; the origin is adjacent to, but distinct from, the origin of pars lateralis.

INSERTION.--_Pars lateralis_ is fused indistinguishably with M. vastus medialis; these two muscles form the main (middle) part of the patellar tendon, which also receives contributions from pars postica and Mm.

femoritibialis internus, extensor iliotibialis lateralis, and extensor iliotibialis anticus; the patellar tendon attaches to the entire rotular crest of the tibia; the patella is situated in the proximal part of this tendon; some deep fleshy fibers of M. vastus lateralis pars lateralis and M. vastus medialis attach to the proximal edge of the patella. _Pars postica_ forms a short narrow tendon that fuses to the lateral part of the tendon of pars lateralis, forming the lateralmost part of the patellar tendon. A broad flat vinculum extends from the lateral surface of the femorofibular fascia (defined under M. flexor perforans et perforatus digiti II) to the deep surface of the lateral part of the patellar tendon; a similar vinculum extends from the medial surface of the internal condyle to the deep surface of the medial part of the patellar tendon.

INNERVATION.--Two or more branches of the middle division of the femoral nerve penetrate the anterior surface of the fused Mm. vastus lateralis (pars lateralis) and vastus medialis; short twigs emerge from the deep surface of pars lateralis and penetrate the superficial surface of the anteroproximal part of pars postica.

INDIVIDUAL VARIATION.--The proximal ends of M. vastus medialis and M.

vastus lateralis are usually separated by a deep notch. In some legs, a small bundle of fibers forming the anteroproximal part of M. vastus lateralis attaches to the lateral surface of M. vastus medialis anterior to this notch.

_T. cupido_

INDIVIDUAL VARIATION.--One leg shows the same variation found in _T.

pallidicinctus_ (see above). In several legs, pars lateralis does not extend so far proximally as usual, but begins at the level of insertion of M. piriformis (does not contact the insertion of M.

iliotrochantericus medius) and may not overlap M. iliacus. In a few legs, no vincula are a.s.sociated with the patellar tendon.

_P. p. jamesi_

INDIVIDUAL VARIATION.--Pars lateralis often begins proximally at the level of the insertion of M. piriformis.

=_M. Vastus Medialis_= (Part of M. femoritibialis medius), Figs. 13, 14, 15

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick; on anteromedial surface of femur medial to anterior part of M. vastus lateralis pars lateralis; bounded medially by Mm. ambiens and extensor iliotibialis anticus (distally); bounded posteromedially by M. femoritibialis internus; proximal part medial to posterior ends of Mm. iliacus, iliotrochantericus medius, and gluteus profundus; lateral surface, except proximal part, fused with anterior part of M. vastus lateralis pars lateralis; part of lateral surface of M. vastus medialis covered by sheet of fascia attaching to anterior intermuscular line; M. vastus lateralis separable from this fascia, but fascia absent anteriorly and distally and these two muscles indistinguishably fused.

ORIGIN.--The proximal third is attached narrowly by its lateral edge; the distal two thirds is attached broadly by its entire deep surface.

The proximal third arises tendinously from the trochanteric ridge and the proximal end of the anterior intermuscular line and fleshily from a narrow area of the femur adjacent (medial) to the latter; the distal part arises tendinously from the anterior intermuscular line and fleshily from a broad adjacent area on the anteromedial surface of the femur, terminating distally at the level of the proximal end of the internal condyle; the posterior edge contacts the origin of M.

femoritibialis internus.

INSERTION.--Attachment is in common with M. vastus lateralis pars lateralis, which see.

INNERVATION.--Two or more branches of the middle division of the femoral nerve penetrate the anterior surface of the fused Mm. vastus medialis and vastus lateralis pars lateralis; a variable number of branches of the same division penetrate the medial surface of the proximal part of M. vastus medialis.

INDIVIDUAL VARIATION.--None of significance in any of the three species studied.

=_M. Femoritibialis Internus_=, Figs. 13, 15

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Elongate; on posteromedial surface of femur; bounded anteriorly by M. vastus medialis and posteriorly by M.

adductor profundus (overlapping anterior edge of latter); anteroproximal part lateral to M. ambiens; anterodistal corner deep to distal end of M.

extensor iliotibialis anticus; distal part of muscle split into superficial and deep layers; superficial layer thin, narrow, and tendinous except for proximal end; deep layer wider, much thicker, and fleshy except for distal end taking form of flat tendon; anterior edge of latter somewhat fused to medial edge of tendon of M. vastus medialis; deep layer widest near distal end of fleshy part; posterior edge of superficial layer fused to underlying deep layer, and anterior edge fused to (continuous with) posterior edge of tendon of M. extensor iliotibialis anticus.

ORIGIN.--The origin is mostly fleshy from the posteromedial surface of the femur between the origin of M. vastus medialis and the posterior intermuscular line, terminating immediately proximal to the internal condyle.

INSERTION.--The tendons of both superficial and deep layers attach to the medial part of the rotular crest, forming the medialmost part of the patellar tendon.

INNERVATION.--The posteriormost branch of the middle division of the femoral nerve penetrates the medial surface of the muscle near the proximal end.