is best known as the author of a commentary on the _Cassandra_ of
Lycophron (a poem of 1474 iambic verses by a post-classical tragedian,
about 285 B.C., embodying the warnings of the royal prophetess and
couched in appropriately incomprehensible expressions). It was hardly
worth all the care that Tzetzes lavished upon it. From manuscript
evidence and various claims of John Tzetzes it seems that John worked
over, improved, and enlarged the commentary of his brother. Isaac's
name, however, still remains associated with this particular
exposition.

We are now at length placed in a position to consider the condition
of the ultimate portion of the work, i.e., the last twenty books,
Sixty-one to Eighty inclusive. In general it may be said that for this
section of the history we are thrown back upon an epitome of Ioannes
Xiphilinus, who lived about fifty years earlier than the Ioannes
Zonaras recently under discussion. To this general statement there are
two important exceptions. First, even as early as Xiphilinus wrote
(eleventh century) nearly two books of this last portion had perished.
Book Seventy, containing the reign of Antoninus Pius, was entirely
gone save a few miserable chapters, and Book Seventy-one had suffered
the same fate in its beginning, so that our account of the renowned
Marcus Aurelius begins practically with the year 172 instead of 161.
The gap thus created has been partially filled by extracts of every
conceivable quality and merit, from Suidas, from John of Antioch, even
from Asinius Quadratus. This on the side of loss: on the side of gain
there are numerous little excerpts (just as in the case of the early
books) that may serve to fill crevices or cover scars, and above all
there exists a parchment manuscript, known as Vaticanus 1288, older
than Mediceus A, older than Venetus A, and containing Books
Seventy-eight and Seventy-nine probably very much as Dio wrote them,