First dorsal interosseous muscle of the foot and its innervation.

During dissection of the foot region, it is frequently found that some nerve branches run close to the tibial surface of the second metatarsal bone. To investigate the nerve branches, detailed dissection of the first dorsal interosseous muscle was performed in 10 Japanese adult feet with special reference to its innervation. In all specimens the muscle was clearly separated into lateral and medial parts. The branches ran between these parts and innervated the parts. The small dorsal region of the medial part of the muscle was also innervated by a branch of the deep peroneal nerve. Based on its innervation, the muscle appears to be composed of two elements from the flexores breves profundi and an element from the dorsal primordium. A possible schematic model of the origins of this muscle is proposed.