MUSCLES (continued 2)

Insertion.—The long, slender, ossified tendon extends along the posteromedial aspect of the tibiotarsus and becomes flexible just before attaching to the proximomedial part of the tibial cartilage. The tibial cartilage is a large, mostly cartilaginous pad fitting closely over the posterior surface of the intratarsal joint; the distomedial corner is ossified. This cartilage is perforated by the tendons of several flexor muscles; the distal end of the cartilage attaches to the posteroproximal corner of the tarsometatarsus.

Innervation.—A branch of the medial division of the tibial nerve penetrates the lateral surface.

Individual Variation.—In one leg, a small bundle of fibers separates from the proximal end of the muscle, forming a short accessory head which attaches, separately from the remainder, to the articular capsule posteroproximal to the main origin; a blood vessel passes between the main and accessory heads.

T. cupido

Individual Variation.—In one leg, a small bundle of fibers arises from the medial collateral ligament. In another leg, the nerve to M. gastrocnemius pars interna passes through a gap in the origin of M. plantaris rather than distal to its origin.

P. p. jamesi

Individual Variation.—The nerve branch supplying M. gastrocnemius pars interna gives a minute twig to the deep surface of the free belly of M. plantaris in one instance.

M. Flexor Digitorum Longus, Figs. 14, 16, 17, 19A

T. pallidicinctus

General Description and Relations.—Relatively broad; bipinnate; on posterolateral surface of tibiotarsus; bounded posteromedially by M. flexor hallucis longus, posteriorly by M. flexor perforatus digiti II and anterolateral head of M. flexor perforatus digiti III, laterally by Mm. flexor perforans et perforatus digiti III and flexor perforans et perforatus digiti II, and anterolaterally by Mm. peroneus brevis and tibialis anticus; anterior surface of lateral part of distal half of common belly fused to M. peroneus brevis; divided into three heads—posterior (largest), lateral, and medial; posterior head on posterior surface of head of fibula; overlapping and fused to lateral end of M. popliteus; proximomedial corner deep to latter; lateral head on lateral surface of fibula; lateral and posterior heads separated by insertion of M. extensor iliofibularis; these two heads joined immediately distal to insertion of latter; medial head on posterior surface of tibiotarsus; group of blood vessels and nerves passing between medial and posterior heads; these two heads joined several mm. distal to junction of lateral and posterior heads; deep surface of insertional tendon near distal end of tarsometatarsus serving as origin for M. lumbricalis.

Origin.—Posterior head: This arises fleshily from the posterior surface of the fibula beginning almost at the proximal end and from the medial surface of the fibula beginning deep to the distal part of M. popliteus. Lateral head: This arises fleshily (sometimes partly tendinously) from the lateral surface of the fibula proximal to the fibular tubercle. Some fibers arise from the distal edge of the tendon of insertion of M. extensor iliofibularis. Medial head: This arises fleshily from the posterior surface of the tibiotarsus just medial to the distal part of the posterior head, distal to M. popliteus, and either lateral or distolateral to the origin of M. plantaris. Distal to the junction of the three heads, the muscle arises fleshily from the posterior surface of the tibiotarsus (except the distal part) and from the medial and posterior surfaces of the fibula.

Insertion.—The slender ossified tendon becomes flexible and passes through the canal in the tibial cartilage that lies anterolateral to the canal for M. flexor perforans et perforatus digiti II and anteromedial to the canal for M. flexor perforatus digiti II, then passes through the bony canal of the hypotarsus that is deep to all the other flexor tendons; the tendon ossifies again and lies adjacent (lateral) to the posterior metatarsal crest; the vinculum from the tendon of M. flexor hallucis longus fuses extensively to the superficial surface of the present tendon a short distance below the midpoint of the tarsometatarsus; the tendon is considerably broader below this point than above it. At the level of the first metatarsal, the tendon divides into three branches (unossified) that diverge, each passing through a groove on the ventral surface of the subarticular cartilages ventral to the trochleae, then pass onto the ventral surfaces of digits II, III, and IV. On digit IV the tendon gives off two dorsal fibro-elastic slips before attaching to the ventral surface of the ungual phalanx; one slip attaches to the subarticular cartilage ventral to the third interphalangeal joint, the other to the subarticular cartilage of the fourth joint and may also attach in part to the distal end of the fourth phalanx. On digit III the tendon gives off two dorsal slips before attaching to the ventral surface of the ungual phalanx; one slip attaches to the subarticular cartilage of the second interphalangeal joint, the other to the subarticular cartilage of the third joint and may also attach in part to the distal end of the third phalanx. On digit II the tendon gives off one dorsal slip before attaching to the ventral surface of the ungual phalanx; the slip attaches to the subarticular cartilage of the second interphalangeal joint and may also attach in part to the distal end of the second phalanx.

Innervation.—A branch of the medial division of the tibial nerve penetrates the medial surface of the posterior head.

Individual Variation.—In half the legs, the proximal end of the lateral head is notched for the passage of the peroneal nerve; the main part of the head lies medial to this nerve; the short fleshy slip lateral to this nerve arises by a long, slender, and extremely weak tendon from connective tissue surrounding the femorotibiotarsal joint. In one leg, a bundle of fibers separates from the lateral head and attaches to the terminal four mm. of the anterior (proximal) edge of the tendon of M. extensor iliofibularis. Each of the following variations occurs in several legs: a third dorsal slip on digit IV attaches to the distal end of the fourth phalanx in some legs and to the subarticular cartilage of the fourth joint in other legs; a third dorsal slip on digit III attaches to the distal end of the third phalanx in some legs and to the subarticular cartilage of the third joint in other legs; a second dorsal slip on digit II attaches to the distal end of the second phalanx in some legs and to the subarticular cartilage of the second joint in other legs.

T. cupido

Individual Variation.—The dorsal slips of insertion show variations similar to those noted above for T. pallidicinctus.

P. p. jamesi

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 for T. 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 it becomes 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 for T. 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. The distalmost 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 Typical T. 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. On the 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. On digit IV the tendon subdivides into branches that attach to the proximal ends of the ungual, fourth, third, and (usually) second phalanges. On digit III the 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. On digit II the 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 Typical T. pallidicinctus.—The belly is shorter. The lateral branch of the tendon on the tarsometatarsus is not ossified (true also of some legs of Tympanuchus).

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 II Figs. 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 in T. cupido and P. p. jamesi.

M. Extensor Proprius Digiti III (Not found by Hudson, et al.), Fig. 20N

T. pallidicinctus and T. 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 in T. 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 in T. cupido and P. p. jamesi.

FOOTNOTES: