The following excerpt is from the introduction to Jataka Tales
The Jatakas, or Birth-stories, form one of the sacred books of the Buddhists and relate to the adventures of the Buddha in his former existences, the best character in any story being identified with the Master.
These legends were continually introduced into the religious discourses of the Buddhist teachers to illustrate the doctrines of their faith or to magnify the glory and sanctity of the Buddha, somewhat as medieval preachers in Europe used to enliven their sermons by introducing fables and popular tales to rouse the flagging interest of their hearers. . . .
. . . While some of the stories are Buddhistic and depend for their point on some custom or idea peculiar to Buddhism, many are age-old fables, the flotsam and jetsam of folklore, which have appeared under various guises throughout the centuries, as when they were used by Boccaccio or Poggio, merely as merry tales, or by Chaucer, who unwittingly puts a Jataka story into the mouth of his pardoners when he tells the tale of "the Ryotoures three."
. . . The Jataka Tales contain deep truths, and are calculated to impress lessons of great moral beauty. . . . .these tales "are, as everyone must admit, nobly conceived, lofty in meaning, and many a helpful sermon might be preached from them as texts."