Dorsal interossei
The fourth, or deepest layer of the plantar intrinsic muscles contains the dorsal and plantar interossei muscles. Let us begin with the dorsal. There are four dorsal interossei located in the fourth layer of plantar muscles. Each dorsal interossei arises by two heads from the sides of the shafts of adjacent metatarsal bones and inserts into the bases of the proximal phalanges and their corresponding extensor expansions. Note that the first dorsal interossei inserts into the medial aspect of the base of the proximal phalanx of the second toe whereas all three other tendons insert into the lateral aspects of toes 2-4. It may be useful to remember the acronym DAB to remind yourself of the function of the dorsal interossei - that is, dorsal interossei abduct toes 2-4. These muscles also have a secondary function of stabilizing the transverse arch of the foot.