PROFESSOR HUXLEY ON THE OSTEOLOGY OF THE GENUS GLYPTODON. 63 
second dorsal vertebra. These, however, are not carried upon distinct processes. The 
great spinous process seems completely to fill up the interval which properly exists 
between the postzygapophyses. The posterior face of this process is slightly excavated 
in the middle of its lower half. Its sides are also a little concave, so that the top 
swells out into a sort of knob with overhanging margins. 
The posterior part of the floor of the trivertebral bone is broken away ; but the hinder 
face of each lateral mass exhibits a transversely elongated articular surface ( b , b), concave 
from above downwards, so as to resemble a segment of a hollow cylinder, the axis of 
which is directed from within outwards and very slightly backwards. 
The inferior face of the trivertebral bone presents the arched surface, flatter behind 
than in front, of the continuously ossified central portions or bodies of the vertebrae, 
and, external to these, two pairs of apertures which perforate this face of the bone at 
its outer margin. The anterior of these apertures is very much larger than the poste- 
rior, and corresponds with the inner end of the middle transverse process, opening just 
behind the inner end of the first rib. Strictly speaking, the foramen seen upon the 
front face of the bone (Plate VII. fig. 5, d) forms one of this series of foramina (all of 
which are the terminations of short passages leading into the spinal canal) ; so that, as 
upon the upper, so on the under surface of the trivertebral bone, there are three pairs 
of foramina in communication with the spinal canal, and of these the middle pair are, 
in each series, the largest. 
The homologies of the three vertebrae which compose the trivertebral bone are deter- 
mined by the implantation of the head of the first rib into the great fossa between the 
lateral processes of the first and second. The vertebra which yields the anterior wall of 
the fossa is clearly the last cervical, and that which furnishes the posterior wall is the 
first dorsal. Plence the trivertebral bone is composed of the last, or seventh, cervical and 
the first and second dorsal vertebrae. 
The remaining Dorso-lumbar Vertebrae . — Of these vertebrae thirteen are preserved. 
The anterior twelve have plainly been immoveably united together into a continuous 
arched tunnel or tubular bridge of bone, partly by anchylosis and partly by the manner 
in which their apposed surfaces interlock (Plate VIII. figs. 1-7). 
The four anterior vertebrae (figs. 1, d. 1. 3, 4, 5, 6) are so completely anchylosed together 
that almost all traces of their original distinctness are lost. Persistent sutures, of a cha- 
racter intermediate between a “ harmonia ” and a serrated suture, separate the fourth 
vertebra (d. 1. 6) from the fifth, and the latter from the sixth ; but the sixth and the 
seventh ( d . 1. 9) are completely fused into one bone. Between the eighth and ninth 
vertebrae a suture is interposed, and also between the ninth and the tenth, at least on 
the left side. The tenth and the eleventh [d. 1. 13) are completely anchylosed above, 
while the suture seems to have persisted below *. 
* It is convenient to speak of the first, second, (fee. of the thirteen vertebrae which succeed the trivertebral 
bone ; but it must be recollected that the first of these is the third of the dorso-lumbar series, the second the 
fourth dorso-lumbar, and so on, the number of any one of these vertebrae in the dorso-lumbar series being 
MDCCCLXV. L 
