http://www.tenbulls.com/newest%20bullshite/html/Sculpture.html
Here is a modern day sculpture with an intrepretation of each of the bullherding pictures based on Sung Dynasty Zen Master by the name of Kaku-an Shi-en. This site mentions that they are said to outline the gradual development of the Zen life. (Check out the buffalo picture on the top too. That is beautiful!)