A benign, swollen enlargement of the sheath of nerve that runs across the bottom of the foot and out to the toes. Morton neuroma typically develops in the ball of the foot in the space between the third and fourth toes. The principal symptom is a burning pain in the ball of the foot, often occurring during weight-bearing activities such as walking or using stairs. The pain may also be experienced as an aching, shooting, or tingling pain in the toes. The condition is diagnosed by physical examination or X rays.