Not sure what would be the question here. Isthmian Central America contains all the countries mentioned: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama.
But the southernmost portion of the North American continent, which connects with South America on the southeast it is called the Isthmus of Panama. Also known as the Isthmus of Darien, the Panama isthmus is a narrow strip of land between the Caribbean Sea and the Pacific Ocean, linking North America and South America. It contains the country of Panama and is a place of strategic value.