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. 19]E, [20]N
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).