The "Ox-Herding Pictures" or "Bull-Herder Series"
illustrate the spiritual development of Zen
students, from the moment they enter the Way
until the completion of their training, when
they become masters in their own right. The set
of ten compiled by Master K'uo-an is the most
commonly used. K'uo-an added a verse and
commentary to each picture to indicate the
nature of spiritual practice in that stage.