Extensor digitorum longus
The muscle belly of extensor digitorum longus lies superficial to that of extensor hallucis longus in the anterior leg. It has a similar origin to EHL, but also attaches to the lateral tibial condyle. This muscle has complex insertion points into all four of the lesser digits. Deep to the extensor retinaculum, the tendon of insertion divides into four tendinous slips - one for each of the lesser digits. Each slip then forms a membranous structure known as an extensor expansion over the dorsal aspect of each metatarsophalangeal joint. As it approaches the proximal interphalangeal joint, each extensor expansion divides into three slips. The central slip inserts into the dorsum of the base of the middle phalanx and the two collateral slips unite to form a terminal slip which inserts into the dorsal aspect of the base of the distal phalanx. Extensor digitorum longus is principally responsible for dorsiflexing the ankle and the lesser digits, however, it also assists in everting the foot. To identify the muscle belly and tendons of insertion, ask your subject to dorsiflex both the ankle and their digits while you apply global resistance to the dorsal surface of the lesser toes. The tendinous slips will become prominent along the dorsal foot and ankle and the muscle belly may be traced proximally from there.