Whilst Professor Zimmer's conclusion as to the personality of the L.U. compiler has been challenged, his main thesis has remained unshaken. On the whole, it can be asserted positively that the common source of L.U. and Y.B.L. goes back to the early eleventh century; on the whole, that this common source itself utilised texts similar to those contained in the Book of Leinster. Moreover, the progress of linguistic analysis during the past quarter-century has strengthened the contention that some of the elements used by Flann (or another) in compiling his eleventh-century harmony are as old, in point of language, as any existing remains of Irish outside the Ogham inscriptions; in other words, being as old as the earliest glosses, they may date back to the eighth or even seventh century. In particular the L.U.-Y.B.L. version of the "Tain bo Cuailnge" contains a large proportion of such elements and may, in the main, be treated as an eighth-century text. It must, however, be pointed out, and for this reason I have italicised the qualifying "on the whole," "in the main," that this conclusion does not enable us to declare dogmatically (1) that all portions of the L.U.-Y.B.L. version must go back to the eighth century; (2) that all portions of the Book of Leinster version must precede the compilation of the common source of L.U. and Y.B.L. For as regards (1), not only must the definitely ascertained activity of the eleventh-century compiler be taken into account, but also the possible activity of later scribes. If we possessed the complete text of the L.U.-Y.B.L. redaction in both MSS., we could at least be sure concerning the possible variations introduced during the two centuries that elapsed between the writing of the Yellow Book (early fourteenth century) and that of L.U. (late eleventh century). But most unfortunately both MSS. are imperfect, the Yellow Book at the opening, L.U. at the close of our tale. Thus of the special episode under consideration, the "Combat at the Ford," the older redaction is only extant in the fourteenth-century MS., and it is always open to impugners of its archaic character to say that it has been introduced there from the rival Leinster version. Again, as regards (2), whilst it is practically certain that the great mass of the Leinster version was in existence before the time of the source whence both L.U. and Y.B.L. are derived, and must therefore date back to the early eleventh century, it is by no means certain that this version was not considerably altered and enlarged before it came to be written down in the Book of Leinster some time before 1154.