North America Central America A very narrow isthmus of southern North America extending from the Isthmus of Tehuantepec in Mexico southeastward to the Isthmus of Panama where it connects to the Colombian Pacific Lowlands in northwestern South America. LanguaL curation note: US FDA 1995 Code: QP North America Central America A very narrow isthmus of southern North America extending from the Isthmus of Tehuantepec in Mexico southeastward to the Isthmus of Panama where it connects to the Colombian Pacific Lowlands in northwestern South America. LanguaL curation note: US FDA 1995 Code: QP