Bordered on two sides by water, an isthmus is a relatively narrow strip of land that links larger land masses, such as two islands, a mainland coast with an offshore island, or even two continents. An example of the last is the Isthmus of Panama, which extends from the southern border of Costa Rica to Colombia—linking the North and South American continents. An isthmus that acts as a corridor along which animals and plants migrate from one continent to another is sometimes called a land bridge. In From the Earth to the Moon, Jules Verne observes that an isthmus can also transport a mountain range: “On the west,” Verne writes, “arise the Rocky Mountains, that immense range which, commencing at the Straits of Magellan, follows the western coast of Southern America under the name of the Andes or the Cordilleras, until it crosses the Isthmus of Panama, and runs up the whole of North America to the very borders of the Polar Sea.” The term appears in various coastal place-names, including Isthmus Bay in Alaska; Isthmus Brook in Penobscot, Maine; and Isthmus Slough in Coos Bay, Oregon. While many landscape terms derive from analogy to our own anatomy— neck, mouth, finger, etc.—isthmus seems to be the rarer case in which a geographic term is applied to an analogous feature of the body: anatomically, an isthmus is a narrow band of tissue connecting two larger parts of some corporeal structure.

Emily Hiestand