Abstract
1. A group of cases is presented in which the os intermetatarseum took the form of an intermetatarsal spur, from which (in members of one family) there arose a tendon-like structure whose distal attachment was to the lateral aspect of the proximal phalanx of the great toe. The suggestion is made that this may represent a lost first plantar interosseous muscle.
2. Another effect of the presence of an os intermetatarseum is the production of metatarsus primus varus by its action as a wedge which spreads apart the bases of the two metatarsal bones. A very small wedge may at times produce considerable deviation (Case 4), and resection of the os can result in satisfactory correction.
3. It is also felt that over-development of extensor hallucis brevis may at times contribute to the formation of hallux valgus.
