What breed of dog was Toto?

In the 1939 movie "The Wizard of Oz," Dorothy's dog Toto was played by a cairn terrier. The book's author, L. Frank Baum, never specifically identified Toto's breed. Baum described Toto as a small black dog with long hair, although illustrations typically depict Toto as a cairn or Yorkshire terrier.

Cairn terriers were originally raised by Scottish farmers to help clear vermin from their lands. In Scotland, a "cairn" is the rocky den of a fox or badger. The terrier breed was able to squeeze into the burrow and hold the pest at bay until the farmer exterminated it. Cairn Terriers are alert and active, but they require obedience training and regular exercise.