"Morton's toe,"  the condition of having a first metatarsal which is short in relation to the second metatarsal.  It is a type of brachymetatarsia. 
See also Morton, The human foot: Its evolutionary development, physiology, and function disorders. New York: Columbia University Press, 1935. Morton believed that two major causes of foot problems were the short first metatarsal bone and hypermobility of the first metatarsal bone.