60 PROFESSOR HUXLEY ON THE OSTEOLOG-Y OF THE GENUS GLYPTODON. 
surface looks forwards and inwards. The inner and lower edges of the opposite occi- 
pital facets of the atlas must have been separated by a distance of about 1*9 inch. 
The transverse process of the atlas is, as I have stated, broken off close to its origin ; 
but the cancellated fractured surface, 2 niches long by more than half an inch wide 
superiorly, proves that the process was flattened from before backwards, and that it 
arose from the posterior half of the outer surface of the lateral mass of the bone. The 
surface of attachment of the process is almost perpendicular to that of the axis of the 
spinal canal, or, at most, has a very slight inclination from above downwards and for- 
wards. The general plane of the process, on the other hand, as exhibited by an upper 
or an under view, is directed backwards and outwards. There are no means of judging 
how far the process may have extended outwards. 
The Odontoid and immediately-following Cervical Vertebrae. — The fragment of this 
region of the vertebral column (figured in Plate IX. fig. 5 from without, fig. 6 from 
within, fig. 7 from behind, and fig. 8 from below) is composed of the right half of the 
neural arch of the axis, or odontoid, vertebra, anchylosed together with the arches of the 
third and fourth cervical vertebrae. It formed the right half of the roof and side walls 
of the neural canal in this region. The front face of the bone, thick and prismatic, is 
obliquely bevelled off to a rounded edge, which is concave anteriorly. The outer face is 
produced above into a tuberosity, the anterior part of which is perforated by a canal 
which traverses the whole thickness of the bone and opens on its inner face, near its 
upper end (fig. 5, c , fig. 6, c 1 ). From the tuberosity a small ridge, partly broken away, 
leads forwards and inwards along the anterior face of the bone. A stouter ridge extends 
inwards near the posterior margin of the bone, from the same tuberosity. These two 
ridges were situated upon the proper upper surface of the arch, and probably joined the 
anchylosed spinous processes. 
The lower part of the outer face presents a broken surface, with the outer termina- 
tions of three canals (figs. 5 & 8, d, e,f), the inner ends of which are visible on the inner 
or under surface of the bone (fig. 6, d, e,f) as they traverse its thickness obliquely from 
within outwards and downwards. The hindermost of these canals (d) is wide below, but 
narrows into a fissure above. The second, or middle, foramen (e) is wider, oval, and looks 
more downwards. The third (f) is much smaller than either of the other two. On the 
inner face of the bone (fig. 6) the aperture of the posterior canal ( d ) is longest. The middle 
canal opens upon nearly the same level ; but the third, or anterior, canal takes a much 
shorter course through the bone, and thus its inner end is on a level below the others. 
The aperture of the middle canal is situated at about the same distance from the ante- 
rior margin of the bone as the inner end of that canal ( c , c') which, I have stated, opens 
externally upon the tuberosity. A little aperture (g) in the same line with these two 
leads into the substance of the bone, and seems to have no external outlet. Lines drawn 
through the three apertures referred to, mark off an anterior segment of the bone from 
a middle segment, which is defined, by a line drawn from the inner end of the posterior 
canal below to another small aperture ( h ) above, from a hinder segment. 
