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 headon posterior surface of head of fibula; overlapping and fused to lateral end of M. popliteus; proximomedial corner deep to latter;lateral headon 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 headon 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 distaledge 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. Ondigit IVthe 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. Ondigit IIIthe 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. Ondigit IIthe 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 forT. pallidicinctus.
P. p. jamesi
Individual Variation.—In one leg, the proximal end of the lateral head is notched for the passage of the peroneal nerve. The dorsal slips of insertion show variations similiar to those given above forT. pallidicinctus. In four legs, a tiny vinculum extends from the lateral edge of the branch of the tendon on digit IV to the lateral edge of the underlying medial branch of the tendon of M. flexor perforatus digiti IV at the level of the second phalanx.
M. Popliteus,Fig. 19B
T. pallidicinctus
General Description and Relations.—Extremely short but relatively broad and thick; on posterior surface of proximal end of tibiotarsus; extending distomedially from proximal part of fibula; deep to M. flexor hallucis longus; lateral end overlapped by, and fused to, posterior head of M. flexor digitorum longus; medial end often slightly overlapped by, and fused to, M. plantaris; medial end (insertion) much wider than lateral end (origin).
Origin.—The origin is fleshy and tendinous (superficial surface) from the medial surface of the fibula near the proximal end.
Insertion.—The attachment is fleshy to the posterior surface of the proximal end of the tibiotarsus adjacent (lateral) to the origin of M. plantaris.
Innervation.—A branch of the medial division of the tibial nerve penetrates the posterior surface.
Individual Variation.—None of significance in any of the three species studied.
M. Peroneus Longus,Figs. 12,13
T. pallidicinctus
General Description and Relations.—Large; on anterolateral surface of shank; bounded medially by M. gastrocnemius pars interna and posterolaterally by Mm. flexor perforans et perforatus digiti III and flexor perforans et perforatus digiti II; proximal three fourths of posteromedial part (covered by M. gastrocnemius pars interna) aponeurotic and tightly fused to medial surfaces of underlying Mm. tibialis anticus and extensor digitorum longus; proximal part of fleshy belly somewhat fused to anterior surface of underlying M. tibialis anticus; posterolateral surface strongly fused to aponeurotic medial head of M. flexor perforans et perforatus digiti II and slightly fused to anterolateral edge of M. flexor perforans et perforatus digiti III.
Origin.—The muscle arises by fleshy and tendinous fibers from the edges of the inner and outer cnemial crests; the extreme proximal end arises either fleshily or aponeurotically from the rotular crest between the cnemial crests; the posteromedial edge (aponeurotic except distal one fourth fleshy) arises from the anteromedial intermuscular line.
Insertion.—The narrow ossified tendon on the superficial surface of the distal part of the fleshy belly extends several mm. beyond the belly where itbecomes flexible and divides into two branches. The short, broad posterior branch attaches broadly to the proximolateral corner of the tibial cartilage. The narrow anterior branch passes along the lateral surface of the tibiotarsus, through a strong retinaculum immediately proximal to the external condyle, and crosses the lateral surface of the joint, where it is covered by connective tissue nearly as tough as, and continuous with, the retinaculum; the tendon attaches broadly to the lateral edge of the ossified tendon of M. flexor perforatus digiti III a short distance below the hypotarsus.
Innervation.—The peroneal nerve sends twigs to the deep surface.
Individual Variation.—In both legs of two specimens, the extreme proximal end extends proximal to the rotular crest and attaches fleshily to the superficial surface of the distal end of the patellar tendon.
T. cupido
Individual Variation.—None of significance.
P. p. jamesi
Individual Variation.—One leg shows the variation described above forT. pallidicinctus.
M. Tibialis Anticus,Figs. 14,15,16,19E,20N
T. pallidicinctus
General Description and Relations.—Thick; on anterior aspect of thigh deep to M. peroneus longus; bounded posteriorly by M. extensor digitorum longus and posterolaterally by Mm. flexor digitorum longus and peroneus brevis; divided into two heads—tibial and femoral; small femoral head adjacent to posterolateral surface of much larger tibial head; two heads joined near midpoint of fleshy part of muscle, forming bipinnate belly (pinnate structure most evident on deep surface); proximal part of femoral head situated between outer cnemial crest and head of fibula; proximal part of anterior surface of tibial head somewhat fused to overlying M. peroneus longus; medial surface fused to aponeurosis of latter.
Origin.—Tibial head: This arises by fleshy and tendinous fibers from the edge of the inner cnemial crest, from the rotular crest between the inner and outer cnemial crests, and from the anterior surface, distal edge, and posterior surface of the outer cnemial crest; the attachment may or may not extend onto the superficial surface of the distal part of the patellar tendon; the attachment is adjacent to the origin of the underlying M. extensor digitorum longus.Femoral head: This arises by a slender tendon from the notch in the distal end of the external condyle of the femur.
Insertion.—The slender ossified tendon extends along the anterior surface of the distal end of the tibiotarsus and passes through a large, strong, oblique retinaculum (superficial to the supratendinal bridge); the lateral end of the retinaculum attaches to the lateral end of the supratendinal bridge; the medial end attaches immediately proximal to the medial end of the bridge. The tendon widens and becomes flexible as it passes across the anterior surface of the intratarsal joint, then narrows and attaches to the tubercle on the anterior surface of the proximal part of the tarsometatarsus between Mm. extensor hallucis longus and extensor brevis digiti IV. Thedistalmost bundle of tendinous fibers does not attach to the tubercle, but extends distally along the anterior surface of the tarsometatarsus and attaches to the latter a few mm. distal to the tubercle, forming an accessory insertion. A part of the peroneal nerve passes between the main and accessory insertions.
Innervation.—A variable number of branches of the peroneal nerve penetrate the lateral surface of the femoral head; a variable number of branches of the same division pass deep to the femoral head and enter the posterior edge of the tibial head.
Individual Variation.—- In one leg, the accessory insertion is absent.
T. cupido
Individual Variation.—None of significance.
P. p. jamesi
Differences from TypicalT. pallidicinctus.—The origin of the tibial head does not extend onto the patellar tendon.
Individual Variation.—The accessory insertion is absent in one leg.
M. Extensor Digitorum Longus,Figs. 15,17
T. pallidicinctus
General Description and Relations.—Bipinnate; on anterior surface of tibiotarsus deep to M. tibialis anticus; bounded laterally by M. peroneus brevis; lateral edge usually slightly fused to proximal half of latter; medial surface fused to aponeurosis of M. peroneus longus.
Origin.—The muscle arises fleshily from the lateral surface of the inner cnemial crest, from the rotular crest between the cnemial crests (deep to the attachment of M. tibialis anticus), from the basal (medial) half of the anterior surface of the outer cnemial crest, and from the anterior surface of the tibiotarsus (except the distal part) between the anteromedial and anterolateral intermuscular lines; proximal to the anterolateral intermuscular line, the origin usually extends almost to the lateral edge of the tibiotarsus.
Insertion.—The ossified tendon extends along the mid-anterior surface of the distal part of the tibiotarsus deep to the tendon of M. tibialis anticus and passes under the supratendinal bridge, becoming flexible and widening slightly as it crosses the anterior surface of the intratarsal joint; the tendon narrows again and passes through a small but strong retinaculum on the anterior surface (medial to midline) of the proximal part of the tarsometatarsus; the retinaculum is immediately proximal and medial to the insertion of M. tibialis anticus. The tendon ossifies again as it passes down the anterior surface of the tarsometatarsus and bifurcates near the midpoint of the latter; the lateral branch soon bifurcates again; of these three branches, which are ossified for some distance, the lateral one passes onto the dorsal surface of digit IV, the middle one passes onto the dorsolateral surface of digit III, and the medial one subdivides (at the level of the trochleae) into three branches—one passing onto the dorsal surface of digit III and two passing onto the dorsal surface of digit II. At the level of the metatarsophalangeal joints, all of these tendons are interconnected by strong sheets of connective tissue and it is often difficult exactly to delimit the tendons at this level. Onthe digits, tough connective tissue binds the tendons to the phalanges; this is most pronounced at the interphalangeal joints. The tendons are distinct on the first phalanx of each digit, but are often poorly defined farther distally. Ondigit IVthe tendon subdivides into branches that attach to the proximal ends of the ungual, fourth, third, and (usually) second phalanges. Ondigit IIIthe lateralmost tendon bifurcates, with one branch attaching to the ungual phalanx and the other to the proximal end of the third phalanx; the medial tendon attaches to the proximal end of the second phalanx. Ondigit IIthe originally medial tendon passes underneath and then lateral to the other tendon and attaches to the ungual phalanx; the other tendon attaches to the proximal end of the second phalanx.
Innervation.—One or more branches of the peroneal nerve enter the lateral edge.
Individual Variation.—In four legs, the lateral branch of the trifurcated tendon is not ossified at all.
T. cupido
Individual Variation.—In a few cases, the muscle does not come in contact with M. peroneus brevis.
P. p. jamesi
Differences from TypicalT. pallidicinctus.—The belly is shorter. The lateral branch of the tendon on the tarsometatarsus is not ossified (true also of some legs ofTympanuchus).
Individual Variation.—In several legs, the muscle also arises from the distal part of the posterior surface of the outer cnemial crest.
M. Peroneus Brevis,Figs. 14,16,17,188,19A
T. pallidicinctus
General Description and Relations.—Small; on lateral surface of distal part of tibiotarsus; mainly anterior to fibula; bounded posteriorly and laterally by M. flexor digitorum longus (fused with latter), anteriorly by M. tibialis anticus, and anteromedially by M. extensor digitorum longus (usually slightly fused to latter).
Origin.—The muscle arises by fleshy and tendinous fibers from the medial and anterior surfaces of the fibula beginning a short distance below the distal end of the fibular crest and from the anterolateral surface of the tibiotarsus anterior to the fibula; the anteromedial edge attaches to the anterolateral intermuscular line.
Insertion.—The short, slender, ossified tendon passes along the anterolateral surface of the tibiotarsus and through a retinaculum immediately proximal and anteromedial to the retinaculum for the anterior branch of the tendon of M. peroneus longus; the tendon becomes flexible and widens as it passes across the lateral surface of the intratarsal joint deep to the tendon of M. peroneus longus, turning posteriorly and attaching to the proximolateral corner of the hypotarsus.
Innervation.—The superficial peroneal branch of the peroneal nerve gives one or two twigs to the anterior surface of the proximal part.
Individual Variation.—None of significance.
T. cupido
Individual Variation.—In a few legs, the muscle does not come in contact with M. extensor digitorum longus.
P. p. jamesi
Individual Variation.—None of significance.
M. Extensor Hallucis Longus,Figs. 19E,20N
T. pallidicinctus
General Description and Relations.—Slender and elongate; proximal part on anterior surface of tarsometatarsus medial to anterior metatarsal groove; near midlength of tarsometatarsus, muscle twisted onto medial surface of latter; divisible into two heads—proximal and distal; belly of proximal head (largest) ending at level of twisting onto medial surface of bone; short distal head beginning at this point deep to tendon of proximal head and soon joining latter tendon.
Origin.—Proximal head: This arises fleshily from the anterior surface of approximately the proximal half of the tarsometatarsus medial to the anterior metatarsal groove; the proximal end is partly medial to and partly deep to the retinaculum for M. extensor digitorum longus; some fibers arise from the extreme distal edge of the main insertion of M. tibialis anticus; the distal end of the belly is unattached.Distal head: This arises fleshily from the medial surface of the tarsometatarsus proximal to the first metatarsal and deep to the tendon of the proximal head.
Insertion.—The slender tendon of the proximal head, which begins along the medial edge of the distal part of the belly, soon fuses with the superficial surface of the distal head (ossified here); the common tendon (unossified) passes onto the dorsal (proximal) surface of the first metatarsal, where it passes through a retinaculum, then passes along the dorsal surface of the hallux (bound by strong connective tissue to the metatarsophalangeal joint), attaching to the dorsal surface of the ungual phalanx.
Innervation.—The branch of the deep peroneal nerve that passes medial to the main insertion of M. tibialis anticus gives one or two twigs into the proximal part of the proximal head. No supply to the distal head was found, but see below.
Individual Variation.—In one leg, the proximal end of the distal head is fused to the distal end of the belly of the proximal head, whereas in three legs, a distinct gap separates the fleshy parts of the two heads. The following variations, each found in one leg, pertain to the relationship of the origin of the proximal head to the retinaculum for M. extensor digitorum longus: the origin does not extend proximally medial to the retinaculum; the origin does not extend proximally deep to this retinaculum; a part of the proximal end extends proximally lateral to this retinaculum (in this instance there is an unusually wide gap between the retinaculum and the insertion of M. tibialis anticus). In one leg, the distalmost fibers of the distal head do not join the common tendon but insert independently on the articular capsule of the metatarsophalangeal joint (deep to the common tendon).
T. cupido
Individual Variation.—The relationship between the two heads varies as follows: the proximal end of the distal head may be fused to the distal end of the belly of the proximal head; the proximal end of the distal head may begin anterior (adjacent) to the distal end of the belly of the proximal head; there may be a distinct gap between the fleshy parts of the two heads. In two legs, there is no origin from the insertion of M. tibialis anticus. In one leg, a small accessory bundle of fleshy fibers arises from the proximal end of the first metatarsal (widely separated from the origin of the distal head), passes through the retinaculum deep to the common tendon and attaches to the dorsal surface of the articular capsule of the metatarsophalangeal joint; thus this bundle is completely separate from the remainder of the muscle. In two legs, the same nerve branch that gives twigs into the proximal head also gives off (much farther distally) a twig that enters the distal head.
P. p. jamesi
Individual Variation.—The proximal end of the distal head may begin anterior (adjacent) to the distal end of the belly of the proximal head. In four legs, the origin of the proximal head does not extend proximally medial to the retinaculum for M. extensor digitorum longus; in one of these legs, a part of the proximal end extends proximally lateral to this retinaculum. The distalmost fibers of the distal head do not join the common tendon but insert independently on the dorsal surface of the articular capsule of the metatarsophalangeal joint in four legs; in another leg, the entire distal head has the latter insertion (consequently the two heads are completely separate).
M. Abductor Digiti IIFigs. 19E,20N
T. pallidicinctus
General Description and Relations.—Short; on medial surface of distal part of tarsometatarsus; proximal end adjacent (anterior) to distal head of M. extensor hallucis longus.
Origin.—The origin is fleshy from the medial surface of the distal part of the tarsometatarsus anterior (adjacent) to the first metatarsal and from the anteromedial surface of the basal half of the first metatarsal.
Insertion.—The flat tendon passes over the medial surface of the trochlea for digit II and attaches to the medial surface of the proximal end of the first phalanx of digit II; the tendon is fused with the articular capsule.
Innervation.—The compound nerve formed by the fusion of a branch of the superficial peroneal nerve with a branch of the deep peroneal nerve gives a twig to the anterolateral edge of the muscle.
Individual Variation.—In some cases, the twig arises from the deep peroneal branch alone (which is not joined by the superficial peroneal nerve).
T. cupido
Individual Variation.—In one leg, some of the fleshy fibers arising from the first metatarsal insert independently on the medial surface of the trochlea for digit II (deep to the main part of the muscle).
P. p. jamesi
Individual Variation.—None of significance.
M. Extensor Brevis Digiti III(M. extensor proprius digiti III),Figs. 19E,20N
T. pallidicinctus
General Description and Relations.—Short and relatively broad (narrow proximally); on mid-anterior surface of distal part of tarsometatarsus; tendon of insertion fused with articular capsule.
Origin.—The origin is fleshy from the mid-anterior surface of the distal part of the tarsometatarsus ending a short distance proximal to the trochlea for digit III.
Insertion.—The flat tendon passes over the trochlea for digit III and attaches to the dorsal surface of the proximal end of the first phalanx of digit III.
Innervation.—The compound nerve formed by the fusion of a branch of the superficial peroneal nerve with a branch of the deep peroneal nerve gives a twig to the proximal end of the muscle.
Individual Variation.—In some cases, the twig arises from the deep peroneal branch alone (which is not joined by the superficial peroneal nerve). The individual variation is insignificant inT. cupidoandP. p. jamesi.
M. Extensor Proprius Digiti III(Not found by Hudson,et al.),Fig. 20N
T. pallidicinctusandT. cupido
Absent in both species.
P. p. jamesi
This atypical muscle was found in only two legs (P.p. 1L and 4L). The following description applies to P.p. 4L (Fig. 20N).
General Description and Relations.—Small but well developed; fleshy part 1½ × 13 mm.; proximal end narrower; on mid-anterior surface of tarsometatarsus between Mm. extensor brevis digiti IV and extensor hallucis longus and mostly proximal to M. extensor brevis digiti III; tendinous distal part superficial to latter; fleshy belly ending immediately distal to proximal end of latter.
Origin.—The origin is fleshy from a narrow elongate area on the mid-anterior surface of the tarsometatarsus between Mm. extensor brevis digiti IV and extensor hallucis longus, beginning at the distal end (bony) of the elongate accessory insertion of M. tibialis anticus. The distal part of the belly is free.
Insertion.—The attachment is by a thin, wide (relative to belly) tendon to the superficial surface of M. extensor brevis digiti III.
Innervation.—Not found.
Individual Variation.—In P.p. 1L, the muscle is less well developed. The fleshy belly is 1 × 5 mm. It arises from the lateral edge of M. extensor hallucis longus. The extremely slender insertional tendon attaches as above.
M. Extensor Brevis Digiti IV,Figs. 19E,20N
T. pallidicinctus
General Description and Relations.—Slender and tapering; on lateral part of anterior surface of tarsometatarsus; length of belly variable; middle of medial edge in contact with M. extensor hallucis longus.
Origin.—The origin is fleshy from the lateral part of the anterior surface of the tarsometatarsus, including the anterior metatarsal groove.
Insertion.—The long slender tendon enters the anterior aperture of the distal foramen, passes through the intertrochlear canal, emerges from the terminal foramen, and attaches to the medial surface of the proximal end of the first phalanx of digit IV.
Innervation.—The superficial peroneal branch of the peroneal nerve sends a twig into the proximal part of the muscle.
Individual Variation.—None of significance in any of the three species studied.
M. Lumbricalis,Fig. 19F
T. pallidicinctus
General Description and Relations.—Small, thin, and strap-shaped; on mid-posterior surface of distal end of tarsometatarsus deep to tendon of M. flexor digitorum longus; belly partly fleshy and partly elastic connective tissue.
Origin.—The muscle arises from the deep (anterior) surface of the tendon of M. flexor digitorum longus a short distance proximal to the trifurcation of the latter.
Insertion.—The muscle attaches to the proximal end of the subarticular cartilage ventral to the trochlea for digit III.
Innervation.—A long but extremely small twig arises from the paraperoneal branch of the tibial nerve a short distance distal to the hypotarsus and extends distally along the mid-posterior surface of the tarsometatarsus (parallel to a larger nonmuscular branch) and enters the deep surface distal to the middle. It was possible to follow this twig in only two legs; it was presumably destroyed in the course of dissection in the others.
Individual Variation.—In some cases, the "muscle" appears grossly to be entirely connective tissue, although a distinct entity.
T. cupido
Individual Variation.—In some cases, the "muscle" appears grossly to be entirely connective tissue. The innervation was found in only one leg, in which the twig arises more distally than inT. pallidicinctus.
P. p. jamesi
The innervation was not found.
M. Abductor Digiti IV,Fig. 19F
T. pallidicinctus
General Description and Relations.—Slender and elongate; on posterior surface of tarsometatarsus lateral to midline; in contact with M. flexor hallucis brevis in midline.
Origin.—The origin is fleshy from the posterior surface of the tarsometatarsus lateral to the midline beginning near the proximal end (lateral to the hypotarsus) and ending at the level of the first metatarsal.
Insertion.—The slender tendon, which begins along the lateral edge of the distal part of the belly, passes through a retinaculum on the posterolateral surface of the tarsometatarsus immediately above the outer trochlea and attaches to the lateral surface of the proximal end of the first phalanx of digit IV.
Innervation.—The paraperoneal branch of the tibial nerve gives one or two twigs to the proximal part of the muscle.
Individual Variation.—None of significance in any of the three species studied.
M. Flexor Hallucis Brevis,Fig. 19F
T. pallidicinctus
General Description and Relations.—Slender and elongate; on posterior surface of tarsometatarsus medial to midline; belly (except proximal end) adjacent (lateral) to posterior metatarsal crest; proximal end passing under latter (immediately distal to hypotarsus) and lying anteromedial to hypotarsus.
Origin.—The origin is fleshy from the medial metatarsal depression and from the posterior surface of the tarsometatarsus between the midline and the posterior metatarsal crest beginning immediately below the hypotarsus and ending a short distance above the first metatarsal (sometimes more proximally).
Insertion.—The slender tendon, which begins along the medial edge of the distal part of the belly, passes through the groove on the posterodistal surface of the first metatarsal and onto the proximal end of the ventral surface of the hallux; the tendon widens considerably and attaches by its edges to the ventral surface of the proximal end of the first phalanx, forming a short "tunnel" through which the tendon of M. flexor hallucis longus passes.
Innervation.—The paraperoneal branch of the tibial nerve sends one or two twigs into the proximal part of the muscle (but distal to the hypotarsus).
Individual Variation.—In two legs, the muscle arises in part from the distal end of the lateral calcaneal ridge. The individual variation is insignificant inT. cupidoandP. p. jamesi.
FOOTNOTES:
Analysis of Individual Variation
Considerable individual variation occurs in both the muscles and the nerves of the leg of the three species studied. The amount of variation reported by a worker depends in large part on the degree of variation that he considers significant.
Individual variation in the muscles and in the nerves will be discussed separately; that of the muscles (excluding innervation) will be considered first.
Muscles
Considering the number, rather than degree, of variations, the most variable muscles are: Mm. flexor digitorum longus, obturator, caudofemoralis, and extensor hallucis longus. The first-mentioned muscle exhibits 14 different variations in the specimens studied. Mm. vastus lateralis, flexor perforans et perforatus digiti II, and piriformis also showed a considerable number of variations. The following muscles did not exhibit any variations considered significant in this study: Mm. vastus medialis, femoritibialis internus, flexor perforatus digiti III, extensor brevis digiti III, and abductor digiti IV.
Muscles showing a greatdegreeof individual variation included the following: M. extensor proprius digiti III was present in two legs ofPedioecetesbut absent in the other legs studied. A fleshy muscle slip connected M. caudofemoralis pars caudifemoralis with the tendinous raphe between Mm. flexor cruris lateralis and femorocruralis in two legs, whereas in others this connection was tendinous or even absent altogether. M. caudofemoralis pars caudifemoralis had a tendinous area within the belly in only three legs. A vinculum connected the insertional tendons of Mm. flexor perforans et perforatus digiti II and flexor perforatus digiti II in only one leg. The fleshy belly of M. iliotrochantericus medius was completely split into two parts in one leg. M. flexor cruris lateralis had an accessory slip arising from the caudal musculature in one leg.
Certain individual variations reported in the accounts of the muscles formed a graduated series, as far as degree is concerned, from the typical to the extreme condition. Therefore it was difficult or impossible in some cases to state whether or not certain specimens exhibited such a variation. Elimination of the doubtful instances of variation leaves a total of 50 different variations (excluding variations between species) which can be attributed to a definite number of specimens. The remainder of the discussion of individual variation in the muscles concerns these 50 variations. See table 3.
The typical condition of any structure is considered to be the condition of that structure in the majority of the legs studied. Some conditions considered as typical in the present study might not be so considered if a larger number of specimens had been studied. If exactly half of the legs of one species shows a particular conditionof a structure, the condition typical for this species is considered (for purposes of the following discussion) to be that found in the majority of the legs of the other species.
In all instances except two (of 50) the typical condition of the muscles inT. pallidicinctuswas also the typical condition inT. cupido. The majority of the legs inT. cupidohad an additional dorsal slip on the tendon of M. flexor digitorum longus in digits II and III. In all instances except seven the typical condition inT. pallidicinctuswas also the typical condition inPedioecetes. In these seven instances a variation in the former was the typical condition in the latter. These were: an additional dorsal slip on the tendon of M. flexor digitorum longus in each of three digits, a vinculum between the latter and M. flexor perforatus digiti IV, a partly fleshy insertion of M. flexor cruris medialis, an unossified lateral branch of the insertional tendon of M. extensor digitorum longus, and an independent insertion of the distalmost fibers of the distal head of M. extensor hallucis longus. For all characters except the number of the dorsal slips on the tendon of M. flexor digitorum longus in digits II and III, the typical condition inT. pallidicinctuswas also the typical condition for all species considered together. To facilitate comparison, in the following discussion all of the above-mentioned characters are considered in all species as variants from the typical condition.
Certain legs showed a greater number of variations from the typical condition than did others. The majority of legs showed from four to seven variations in the muscles of the leg. The extremes were P.p. 1L, which showed 11, and T.c.p. 2L, which exhibited only one variation.
Twenty-three of the 50 variations were found in only one leg (out of 23). It would be expected that if additional specimens were studied, more kinds of variations would be found. Nine variations were found in only two legs, five in three legs, five in four legs, and four in five legs. One variation was found in nine legs, one in ten legs, and two in 12 legs; the last four variations were in the number of dorsal slips of the insertional tendon of M. flexor digitorum longus in digits II, III, and IV and in the ossification of the insertional tendon of M. extensor digitorum longus.
Five of the variations were found only in specimens in which only one leg was dissected. Considering only those eight specimens in which both legs were dissected, five of the 45 variations were found in both legs of each specimen exhibiting the variation;28 variations were found in only one leg of each specimen exhibiting the variation; 12 variations were found in both legs of some specimens but in only one leg of other specimens. Of the six muscle features showing the greatest degree of individual variation (described previously), only two (both pertaining to M. caudofemoralis) were found in both legs of the specimens exhibiting the variation.
For one leg (the one showing the most variations) of each specimen of which both legs were studied, the number of variations that this leg had in common with every other leg (of all species) was determined. Then the number of variations in common between the two legs of one individual was compared with the number of variations in common between one leg of this individual and each leg of every other individual. See table 4. One leg of six of the eight specimens showed at least as many variations in common with a leg of another individual as with the other leg of the same individual. The two exceptions were T.p. 2R and T.c.a. 1R. Thus for most specimens there was as much variation in the muscles between the right and left legs of one individual as there was between individuals.
Of the 50 muscle variations seven were found only inT. pallidicinctus(eight legs), 16 were found only inT. cupido(nine legs), and ten were found only inPedioecetes(six legs). Two were found in both species ofTympanuchus(but not inPedioecetes). Fifteen were found in bothTympanuchusandPedioecetes; of these, five were found in all three species studied, eight were shared byT. pallidicinctusandPedioecetes, and two occurred inT. cupidoandPedioecetes.
Nerves
The lumbosacral plexus, femoral nerve, sciatic nerve, and tibial nerve all showed numerous individual variations. The peroneal nerve, however, was relatively constant. Variations in the obturator nerve were considered to be insignificant. See table 5.
In all instances except one (of 40) the typical condition inT. pallidicinctuswas also the typical condition inT. cupido. In most of the legs of the latter the nerve to M. flexor cruris lateralis did not perforate M. caudofemoralis. In all instances except four the typical condition inT. pallidicinctuswas also the typical condition inPedioecetes. These exceptions were: prefixation of the lumbosacral plexus, six roots of the sciatic nerve, femoral nerve formed mainly from S2 to S4 and two twigs to M. flexor ischiofemoralis.In all instances the typical condition inT. pallidicinctuswas also the typical condition for all species considered together.
Certain legs showed a greater number of variations from the typical condition of the nerves than did others. The greatest number of variations was shown by P.p. 3L, which had 12. T.p. 1R and T.c.p. 1L both showed only one.
All six variations in the lumbosacral plexus were found on both sides of each specimen exhibiting the variation. In marked contrast to the other nerves, there was no significant variation in the lumbosacral plexus between the right and left sides of one individual. (This might not always be true, however, if a larger number of specimens were studied.) Of the variations in the lumbosacral plexus, one was found in only one specimen (of 15), one was found in three specimens, one in four specimens, two in six specimens, and one in seven specimens. Of the 34 variations found in the other nerves, 14 were found in only one leg (of 23), six occurred in two legs, four in three legs, three in four legs, three in five legs, two in six legs, one in seven legs, and one in nine legs.
Four of the variations were found only in specimens in which only one leg was dissected. Considering only those eight specimens in which both legs were dissected, and excluding the lumbosacral plexus, ten of the 30 variations were found in both legs of each specimen exhibiting the variation; 16 variations were found in only one leg of each specimen exhibiting the variation; four variations were found in both legs of some specimens but in only one leg of other specimens.
The number of variations in common between the two legs of one individual was compared with the number between individuals in the same manner as for the muscles; the lumbosacral plexus was excluded from consideration. See table 6. One leg of six of the eight specimens showed at least as many variations in common with a leg of another individual as with the other leg of the same individual. The two exceptions were T.p. 2L and T.p. 3R. Thus for most specimens there was as much variation in the nerves other than the lumbosacral plexus between the right and left legs of one individual as there was between individuals.
Of the 40 nerve variations (including the lumbosacral plexus) 11 were found only inT. pallidicinctus, seven were found only inT. cupido, and seven were found only inPedioecetes. Four were found in both species ofTympanuchus(but not inPedioecetes). Eleven were found in bothTympanuchusandPedioecetes; ofthese, four were found in all three species, three were shared byT. pallidicinctusandPedioecetesand four occurred inT. cupidoandPedioecetes.
The average number of variations per leg in both muscles and nerves was 11 inT. pallidicinctus, nine inT. cupido, and 16 inPedioecetes. The high number in the last is in part the result of these being variations from the typical condition ofT. pallidicinctus(rather than fromPedioecetes).
Analysis of Variation Between Species
No constant differences in the muscles or nerves was found betweenT. cupido pinnatusandT. cupido attwateri. Only one constant difference was found betweenT. cupidoandT. pallidicinctus: a thicker fleshy origin of M. extensor iliotibialis lateralis inT. cupido(associated with a thicker edge of the lateral iliac process).
Although no constant differences in the nerves were found betweenPedioecetesandTympanuchus(both species), 17 constant differences in the muscles were found between these two genera. Seven of these differences pertain to features of a single muscle—M. flexor cruris medialis. Compared with the condition inTympanuchus, M. flexor cruris medialis inPedioeceteshas a wider origin, a partly fleshy (instead of entirely tendinous) origin, a more pronounced curvature of the line of origin, a wider insertion, an insertion posterior (rather than anterior) to the medial collateral ligament, an insertion that attaches in part to the articular capsule, and a shorter tendon of insertion (resulting in the fusion of the common insertional tendon of Mm. flexor cruris lateralis and femorocruralis with the fleshy belly rather than with the insertional tendon). Other differences include the following. A more extensive posteroproximal aponeurosis of M. extensor iliotibialis lateralis inPedioecetes(resulting in a narrower fleshy origin); a more nearly straight line of origin of this muscle (associated with a less pronounced lateral iliac process); a thinner fleshy origin of this muscle (associated with a thinner edge of the lateral iliac process); a wider M. flexor cruris lateralis that is fleshy up to the origin from the vertebrae; a wider fleshy origin of M. iliacus; the origin of M. caudofemoralis pars iliofemoralis not reaching the ventral edge of the ischium; a narrower origin of M. adductor superficialis; a wider M. femorocruralis; and a shorter belly of M. extensor digitorum longus. Some additional differences between these two genera, which are slight in degree, are given in the accountsof the muscles. If additional specimens were studied, some of the differences listed above possibly would prove to be subject to individual variation and so could not properly be listed as constant differences between the two genera.
The picture of the differences betweenTympanuchusandPedioecetesthat the present study presents is radically different from that presented by the study of Hudson,et al.(1959). These authors reported the following differences between these two genera. (I am using my terminology.) The origin of M. piriformis is narrower inPedioecetesand is more posteriorly situated; the belly of M. extensor iliotibialis anticus is broader inPedioecetes; the belly of M. tibialis anticus is longer; the belly of M. peroneus brevis is shorter; the insertional tendon of the anterolateral head of M. flexor perforatus digiti III is shorter; the belly of M. flexor digitorum longus is shorter; only two (rather than three) of the branches of M. extensor digitorum longus on the tarsometatarsus are ossified; the posterior metatarsal crest is shorter; M. flexor perforans et perforatus digiti II has two heads inPedioecetesbut only one inTympanuchus; the roof over the hypotarsal canal enclosing the tendon of M. flexor digitorum longus is bony inPedioecetesbut fibrous inTympanuchus; M. flexor cruris lateralis is wider inPedioecetes; and the origin of M. femorocruralis is wider. I paid particular attention in my study to these 13 features given by Hudson,et al.; of these the only differences that I found to be constant were the last two. The apparent reason for this great discrepancy is the small number of legs ofTympanuchusstudied by Hudson,et al.They studied eight legs ofPedioecetesbut only two legs ofTympanuchus. This emphasizes the danger of making comparisons based on a very small number of specimens (a criticism which may prove to apply to the present study as well). The reason why Hudson,et al.did not report most of the differences found by me is not so apparent. Either the specimens studied by the former workers showed a greater variation in these characters than did my specimens or else those workers overlooked the differences. Probably both factors are involved. It remains to be determined how many specimens need to be studied in order to obtain a fairly accurate picture of variation.
Comparison with Other Studies of Innervation
I accept the following concept of muscle-nerve relationship. All muscles of the pelvic limb of birds have developed phylogeneticallyfrom either the dorsal extensor muscle mass or the ventral flexor muscle mass. The former was (at least originally) supplied by only the femoral and peroneal nerves ("dorsal" nerves), the latter by only the obturator and tibial nerves ("ventral" nerves). The best guide for determining which muscles are phylogenetically dorsal and which are ventral seems to be their embryogeny (as shown in the studies of Romer, 1927, and Wortham, 1948). In the phylogenetic changes undergone by the muscles under consideration, the innervation may have changed in some instances, although this is less likely to occur than changes in the attachment or function of the muscles. If a change in innervation has occurred, it would be more likely to be a change from one dorsal nerve to the other or from one ventral nerve to the other rather than from a dorsal nerve to a ventral one orvice versa.
Thus, in my opinion, a report of a dorsal muscle supplied by a ventral nerve, orvice versa, should be viewed with suspicion until it is verified. I suspect that many previous workers have ignored this concept of muscle-nerve relationship, or else do not accept it, since they report, without comment, dorsal muscles (as determined embryologically) innervated by ventral nerves, orvice versa. Owing to the intimate association between the proximal parts of the tibial and peroneal nerves, the true relationship may be difficult to determine. I suspect that this relationship has been misinterpreted by a number of workers. I found inTympanuchusandPedioecetesa branch of the tibial nerve that is closely associated with, and distributed with, the peroneal nerve and has been mistakenly considered a part of the peroneal nerve by some workers. In the study here reported on, I have found no definite exceptions to the expected innervation. The only possible exception is an extra branch, which could not be traced to its origin, supplying M. extensor iliofibularis in one leg. Thus my study of innervation agrees with the embryological determination of the (phylogenetic) dorsal and ventral muscles and lends strong support to the above-stated concept of muscle-nerve relationship.
I have compared my findings on the nerves with those of other workers, who have studied the nerves with a varying degree of thoroughness. The important differences in innervation between these studies and the present one are discussed below.
In neither of Gadow's works did he distinguish tibial and peroneal components in the thigh. In his later work (1891), covering a wide variety of birds, he found that M. piriformis sometimes hasa femoral innervation in addition to the constant sciatic one and that M. gluteus profundus may or may not have a sciatic supply in addition to the femoral one. A comparison of Gadow's terminology of the sciatic nerve branches in the shank and foot (in both works) with mine shows that his branch I represents my peroneal nerve plus my paraperoneal branch of the tibial nerve (Ic); his branch II represents my medial division of the tibial nerve; and his branch III represents my posterior (IIIa) and lateral (IIIb) divisions of the tibial nerve.
Gadow's study (1880) on the ratites includedStruthio,Rhea, andCasuarius. Only inCasuariusdid Gadow find a branch (IIe) of the sciatic nerve supplying Mm. lumbricalis, adductor digiti II, and abductor digiti II. The two former muscles are typically supplied (as inRhea) by the paraperoneal branch of the tibial nerve; Gadow's branch IIe presumably represents a segregated branch of this nerve. More surprising is his finding that M. abductor digiti II is innervated inCasuariusby both the deep peroneal nerve and branch IIe and inRheaby branch Ic (paraperoneal branch of tibial nerve). The deep peroneal innervation is typical. Also unexpected is his finding that the posterior division of the femoral nerve gives minute twigs into M. gastrocnemius pars interna inStruthioandCasuarius. Since the other terminal branches of this nerve in these birds are nonmuscular, since this muscle is chiefly supplied by other nerves, and since the innervation from the femoral nerve is apparently atypical for most birds, the possibility should be considered that the femoral twigs are sensory rather than motor.
Sudilovskaya (1931), studyingStruthio,Rhea, andDromaeus(Dromiceius), used the same terminology as Gadow except that he designates as branch III Gadow's branch Ic. Sudilovskaya's discussion of the main branches of the sciatic nerve is confusing. He states that inStruthio, branches I, II, and III all pass through the tendinous guide loop for M. extensor iliofibularis; this is hard to believe. As near as I can determine, he has mistakenly given the same designation (branch III) to two separate branches (Gadow's Ic and III). There is no problem, however, in determining to which of these two branches he is referring when he is describing the innervation of a particular muscle, since one supplies only muscles of the shank and the other only intrinsic foot muscles. Sudilovskaya found M. abductor digiti II to be innervated by branch III (Ic of Gadow); thus the innervation of this muscle corresponds to that found inRheaby Gadow. Although M. adductor digiti II had the expected innervation from branch III (paraperoneal branch oftibial nerve) inDromaeus, that muscle was found to be supplied by branch II inRhea. (Gadow, on the other hand, reports a typical innervation for this muscle inRhea.) Sudilovskaya found M. peroneus brevis to be supplied by the deep peroneal branch (in contrast to the superficial peroneal supply that I found inTympanuchusandPedioecetes). He found M. gastrocnemius pars interna to be supplied inStruthioby twigs of the femoral nerve in addition to its typical innervation from branch II of the sciatic nerve; this agrees with Gadow's findings in the same genus. Sudilovskaya reports that M. gastrocnemius pars externa was innervated by branches II and III inStruthioandRheaand by branches I and III inDromaeus. (Gadow found only the typical innervation—branch III.)
In the Whooping Crane, Fisher and Goodman (1955) found a peroneal, rather than a femoral, nerve supply for pars postica of M. vastus lateralis. They also report a peroneal nerve supply for M. flexor ischiofemoralis (in contrast to the usual tibial nerve supply) and for M. adductor superficialis (in addition to the usual supply from the obturator nerve). The innervation was not given for the intrinsic foot musculature.
Fisher (1946), studying vultures, reports the following: tibial branches, in addition to the main sciatic branch, supplying M. extensor iliofibularis (typically supplied by the peroneal nerve); an obturator supply, in addition to the usual tibial supply, to M. flexor cruris medialis; a tibial supply, in addition to the typical obturator supply, to M. obturator pars postica; a possible obturator supply, in addition to the typical femoral supply, to M. ambiens; a possible peroneal supply, in addition to the typical tibial supply, to M. flexor digitorum longus; and a peroneal supply to Mm. abductor digiti IV, flexor hallucis brevis, and adductor digiti II (which are typically supplied by the paraperoneal branch of the tibial nerve). Fisher's postfibular branch of the peroneal nerve, which supplies the latter three muscles, apparently represents the paraperoneal branch of the tibial nerve.
Carlsson (1884) did not find a femoral nerve supply for M. gluteus profundus. He found an obturator supply, in addition to the usual sciatic supply, to M. flexor ischiofemoralis inEudyptes chrysolophaandMergulus allebut not in the other two forms studied. He reported a peroneal supply, rather than the expected tibial (paraperoneal) supply, to Mm. abductor digiti IV and adductor digiti IV.
DeMan (1873) found a twig of the obturator nerve supplyingM. flexor ischiofemoralis, in addition to the typical innervation, inCorvus monedula, but not in the few other forms studied. He did not distinguish tibial and peroneal components in the thigh.
Wilcox (1948), studying a loon, did not find any peroneal supply to M. extensor iliotibialis lateralis or to M. gluteus profundus. He found a femoral, rather than a peroneal, supply to M. piriformis. He found an obturator, instead of a tibial, supply to M. flexor ischiofemoralis. (In some of my specimens I found a tiny blood vessel, appearing much like a nerve, emerging from the obturator foramen and entering M. flexor ischiofemoralis.) Wilcox reports an innervation of M. caudofemoralis pars caudifemoralis from the pudendal plexus, in addition to the usual sciatic one. Wilcox did not distinguish tibial and peroneal components in the thigh. In the shank and foot he misidentified the peroneal nerve as the tibial nerve and therefore gave erroneous innervations for all the muscles supplied by this nerve, except for M. adductor digiti IV, which actually should be supplied by the tibial nerve.
Howell (1938) studied only the hip and thigh musculature of the chicken. He overlooked the femoral nerve supply for M. gluteus profundus.
Romer (1927) studied only the hip and thigh muscles of the chick. He did not distinguish tibial and peroneal components in the thigh. He did not mention any sciatic supply for M. gluteus profundus.
Appleton (1928), studied (in various birds) only those muscles of the hip and thigh that are innervated by the tibial and peroneal nerves. He terms the former "ischiadicus ventralis" and the latter "ischiadicus dorsalis." His findings did not differ from mine.
Many differences in the innervation of specific muscles are reported in the literature, even in the same species (by different workers). Some of these differences may be real; others are probably misinterpretations. Consequently more work needs to be done before a complete understanding can be obtained of the innervation of the leg muscles of birds. Especially needed are studies of the tibial-peroneal nerve relationship, perhaps approached by a method other than gross dissection.
FOOTNOTES: