66 PEOFESSOE HUXLEY ON THE OSTEOLOGY OF THE GENUS GLYPTODON. 
base ; and the posterior edge of the thin ridge, which is all that is left of the process, 
appears to incline upwards and forwards. 
The foramina for the exit of the spinal nerves are not intervertebral in the ten 
anterior vertebras, but perforate the bony substance of each vertebra nearer its posterior 
than its anterior boundary. Of these foramina there are two, on each side, for the five 
anterior vertebrae ; one, larger, below the lateral apophysial ridge ; and one, smaller, 
above, or upon, this ridge at the posterior boundary of each vertebra. 
The larger foramen approaches the outer margin of the apophysial ridge, or seems to 
be situated higher up, in each successive vertebra from the first to the seventh. Beyond 
this point the level of the foramen descends somewhat. The eleventh vertebra ( d . 1. 13) 
appears to have possessed a simple intervertebral notch posteriorly, on the left side ; but, 
on the right, a bar of bone is preserved, separating an anterior foramen from the rest of 
the notch, which receives a process of the twelfth vertebra. The arrangement appears 
to be the same in the twelfth vertebra ( d . 1. 14) ; that is to say, the apparent notch has 
been divided by a bar of bone into an anterior nervous foramen, and a posterior articular 
fossa. 
I have briefly referred, above, to the articular surfaces of the eleventh and twelfth 
vertebrae, which are exceedingly irregular and distorted, apparently from partial anchy- 
losis and filling up with osseous matter. A notion of their general character may best 
be obtained by the study of the posterior face of the twelfth vertebra ( d . 1. 14). On 
the upper part of the neural arch, on each side of the spine of this vertebra, irregular 
and partially obliterated posterior oblique processes, or postzygapophyses, are discern*- 
ible. The zygapophysis is separated by a depression, or groove, directed from without 
obliquely downwards and inwards, from a wedge of bone which terminates the apophy- 
sial ridge. Inferiorly and externally, this wedge presents a slightly concave articular 
facet, separated by a deep fossa from a tuberosity with a rounded surface, which passes 
down into the body of the vertebra. On the same level as this fossa, there projects from 
the front surface of the vertebra a triangular process, which fits into a corresponding 
fossa of the eleventh vertebra. The front face of the thirteenth vertebra ( d . 1. 15), again, 
presents, on each side of the neural spine, pits, the floors of which answer to the anterior 
oblique processes, or prezygapophyses; outside of these are ridges, which fit into the fossae 
between the postzygapophysis of the twelfth vertebra and the wedge-shaped process ; 
external to the ridges are fossae which receive those wedge-shaped processes ; and exter- 
nal to and below these, again, are the remains of processes which were received into the 
deep fossae mentioned above. 
Except in the region of these articular processes, neither the anterior nor the poste- 
rior ends of the thirteenth vertebra (Plate VIII. figs. 6 & 7, d l. 15) are entire. Of the 
spinous process, only the base is left ; it thins off anteriorly to a natural edge, which is 
inclined upwards and backwards, and seems to have been quite free. Posteriorly, it 
becomes rapidly thicker ; but its mode of termination cannot be ascertained. The large 
nervous foramen perforates the wall of the vertebra, on a level with the articular pro- 
