574 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
zygapophysis of any preceding vertebra is thus received in the recess between 
pre-zygapophysis and its overarching process. Iam uncertain of the homology 
of this process thus surmounting the true diapophysis; but it may be sup- 
posed to include both anapophysial and metapophysial elements. Owen says 
(Anat. Vert. ii, 865) that in Rodentia “the met- and un-apophyses commence 
by a common tubercle at the fore part of the dorsal series: the anapophysis 
begins to be distinct at the back part of the series, and the metapophyses to 
project from above the anterior zygapophysis; both processes are usually 
well developed in the posterior dorsal and lumbar vertebree ; the diapophysis 
subsides in the posterior corsals, and is lengthened in the lumbars by a coal- 
esced riblet (pleurapophysis) ”. Whatever the theoretical homologies may 
be in this case, the actual formation is as above given ; the structure changes 
suddenly on the 11th dorsal, from which point backward on the 12th and 
13th dorsals, and several succeeding Jumbars, both anapophyses and meta- 
pophyses may be recognized, separate from each other and distinct from the 
probably di-pleur-apophyses of the lumbars, which, with the anapophyses, 
constitute the so-called transverse processes of the lumbar series. On the 
11th dorsal, the last vestige of a true diapophysis has disappeared, and with 
it has gone the above-described plate of bone, which surmounted it in the 
antecedent dorsals. The side of the bone becomes smooth and erect ; along, 
pointed anapophysis projects from the hinder border of the bone, lying 
parallel with the axis of the spinal column. A small, though undoubted 
metapophysis is given off from the pre-zygapophysis, and such metapophysis 
and pre-zygapophysis are together locked in between the anapophysis and 
post-zygapophysis of the antecedent vertebra. Coincidently with this modi- 
fication, the planes of the articular faces of the zygapophyses change from 
nearly horizontal to nearly vertical; rendering the sum of the differences 
between the 10th and 11th dorsals greater than that subsisting between the 
last dorsal and the first lumbar, even taking into consideration the different 
formation of the transverse processes of the lumbar series. Such formation 
continues through the remainder of the dorsal series. 
In the dumbar series, we directly meet, on the 1st lumbar, with a dee 
ently constituted “ transverse” process. The ribs having ended with the last 
dorsal, the lumbars develop at once a lateral plate-like “ transverse ” process, 
which may be theoretically regarded as a di-pleur-apophysis. This plate 
increases in size with successive lumbars, projects with each one more and 
