What is the origin of the idiom "shank's mare" and when to use it?

The idiom "Shanks' mare" or "Shanks' pony" is derived from a colloquial expression that originated in the 19th century. It refers to a person's legs or the act of traveling on foot. The term "Shanks" refers to the lower part of the leg, specifically the shankbone or shinbone, while "mare" or "pony" signifies the act of walking or traveling by foot. The phrase "Shank's mare" is an old-fashioned idiom that refers to traveling on foot or using one's legs as the primary mode of transportation. It suggests that when other means of transportation are not available, relying on one's own legs is the only option.