In the interior of South America the Spanish conquerors had explored the region of the Andes from the isthmus of Panama to Chile.
P. leucilla, one of the best known, has a wide distribution from the isthmus of Panama to Guiana and the valley of the Amazon; but it is one of the most plainly coloured of the family, being black with a white head.
In order to protect the passage of the traffic across the Isthmus of Panama during these disturbed times detachments of United States marines were landed at Panama and Colon, in accordance with the terms of the concession under which the railway had been constructed.
The Isthmus of Panama was probably visited by Alonso de Ojeda in 1499.
Eventually Mexico and New Mexico came to designate the still vaster region of Spanish North America, which (till cut down by changes which have limited the modern republic of Mexico) reached as far as the Isthmus of Panama on the south and took in California and Texas on the north.
It is served by the Panama railway, which crosses the Isthmus of Panama from ocean to ocean.