746 
PROFESSOR OWEN ON THE MEGATHERIUM. 
arch on each side. The axis has a transverse perforation on each side the neural arch 
anterior to the transverse process, which is imperforate. The transverse processes of 
the three succeeding cervicals are imperforate, the vertebral artery entering the neural 
canal behind and perforating obliquely the base of the neurapophysis anteriorly, as in 
the Camelidae. In the sixth cervical, the canal for the vertebral artery runs through 
the base of the transverse process. These processes are much extended antero- 
posteriorly in all the cervicals and overlap each other. The diapophysial and pleur- 
apophysial portions are very distinct in the fifth and sixth cervicals. The spines of the 
third and sixth cervicals inclusive are triangular and pointed ; that of the seventh is 
longer than the rest and truncate above ; it is much exceeded in antero-posterior dia- 
meter by the spine of the first dorsal, but not in height. A metapophysial tubercle 
is developed from the outer side of the anterior zygapophysis in all the five posterior 
cervicals. It is placed more outwardly in the first and second dorsals, and gets upon 
the top of the diapophyses in the succeeding dorsals. In the eleventh dorsal the 
metapophysis (Plate XLIX. fig. 20, m) begins to resume its former position, and 
developes an articular surface (Plate L. fig. 2\, front, m a) from its under part, 
which joins the upper articulating surface (Ib. hack, am) of the anapophysis {a) of 
the preceding vertebra. In the thirteenth dorsal, the metapophysis (/w) is half-way 
between the diapophysis and anterior zygapophysis, and repeats the same articulation 
with the anapophysis. In the last two dorsal vertebrae, the base of the metapophysis 
developes a second articular surface (Plate L. fig. ‘12, front, m %) from its inner side, 
which joins a new or accessory articular surface (ib. hack, z') on the outside of the pos- 
terior zygapophysis of the antecedent vertebra. This tenon-and-mortise articulation 
of the metapophysis with the zygapophysis on the inner side and with the anapo- 
physis on the outer side, is repeated throughout the whole lumbar series. The an- 
apophysis (a) begins to be developed from the anterior dorsal vertebra, and even 
there presents an articular surface (Plate L. fig. 21, hack, a p) at its under part to 
join a corresponding surface {\h. front, pa) on a parapophysis {p) developed from 
the fore and outer part of the neural arch of the succeeding vertebra. In the tenth 
dorsal a second articular surface (ib. hack, am) is established in the upper part of 
the anapophyses for the inferior metapophysial one {m a) of the succeeding vertebra ; 
here, therefore, the anapophysis begins to be mortised between the parapophysial and 
metapophysial articular surfaces, which surfaces continue to the antepenultimate 
lumbar vertebra, from which, forwards, to the eleventh dorsal, there are sixteen 
joints between each pair of vertebrse, as in the Armadillo. But this complication 
goes further in the Great Ant-eater, for, in the penultimate lumbar vertebra, a third 
articular surface (Plate L. fig. 23, hack, a d) is developed from the under and outer 
part of the anapophysis {a), which joins an articular surface (fig. 23, front, d a) on 
the upper and fore-part of the diapophysis of the last lumbar; and this vertebra is 
united in a similarly complex manner with the first sacral vertebra, which would 
make eighteen synovial joints, in addition to those at the ends of the centrum, but 
