They needed a dog with a deep chest, short
legs, and a sturdy tail: The deep chest gives the dog a place to rest his body while his
legs are throwing dirt out of the
hole; the short
legs allows the Scottie to throw dirt to the sides, not back between his
legs; and, the firmly rooted, sturdy and thick tail
allowed the Highlander to pull to the dog back out of the
hole by the tail with the critter firmly locked in the Scottie's huge teeth and powerful jaws.