PROFESSOR HUXLEY OX THE OSTEOLOGY OE THE GENUS GLYPTODON. 67 
cesses, and bifurcates externally, so that one of its apertures ends above, and the other 
below, a stout bar of bone (Plate VIII. fig. 6, a), nearly an inch thick, which ends poste- 
riorly in a raised curved ridge, forming the anterior boundary of a semicircular groove. 
The spinal canal in the thirteenth vertebra is, as I have said, oval in shape, the long 
diameter of the oval (T5 inch in length) being vertical, the short diameter (IT inch) 
transverse. 
As, in the anterior part of the lumbo-sacral region, this canal has a very different 
shape, it is probable that two or three vertebrae are wanting in this portion of the 
spinal column. 
The Sacrum and Coccygeal Vertebrae . — The “ sacrum,” composed of anchylosed lumbar, 
proper sacral, and coccygeal vertebrae, contains at fewest twelve, and perhaps thirteen 
vertebrae. The centra of the two hindermost lumbar vertebrae and of the two proper 
sacral vertebrae, which follow them (Plate IX. fig. 2), are thin and broad bony plates, 
flat above, and slightly concave from side to side below, exhibiting a most marked con- 
trast to the semicylindrical form of the same part in the hindermost of the thirteen 
vertebrae described above. The plane of the plate formed by the centra of the anchy- 
losed lumbar vertebrae is inclined, upwards and forwards, to pass into the general curve 
of the dorso-lumbar region. The plane of the centra of the two succeeding sacral ver- 
tebrae, on the other hand, is horizontal ; and it is obvious, from the characters of the 
rest of the sacrum, that the centra of the following vertebrae, to the end of the sacral 
region, were arranged in an almost semicircular curve, the chord of which is about 18 
inches long (Plate IX. fig. 3). The posterior face of the hindermost coccygeal vertebra 
(Plate IX. fig. 1, a) is broad, oval, and very slightly concave, like the face of an ordi- 
nary vertebral centrum ; but the centrum of the penultimate coccygeal vertebra is much 
flatter and narrower; and this flattening and narrowing become still more marked in 
the centrum of the antepenultimate vertebra and of that which precedes it, or the fourth 
from the end. From this point to the two anterior sacral vertebrae the floor of the 
sacral canal is completely broken away, but there can be little doubt that the missing 
centra were represented by a broad and flat bony plate. 
The neural arches are but imperfectly preserved, except in the lumbar region and 
the anterior part of the sacrum. They are thin, and are separated by large intervertebral 
foramina. In the lumbar vertebrae these foramina pass downwards and backwards into 
grooves which mark the sides of the central plate. Well-defined depressions upon the 
sides of the sacral crest lead upwards and backwards to the canals which pass between 
that crest and the ilia. 
The four last coccygeal intervertebral foramina are still larger, and indicate the 
passage of large nerves to the muscles moving the tail. 
The spinous processes of all the vertebrae which enter into the sacrum, up to the fourth 
from the end inclusively, are anchylosed together into a long and strong osseous crest 
(Plate IX. figs. 3 & 4), which expands above, so as to present a broad and very rugged 
superior face. This crest is 8 inches high in front, but slowly diminishes as it follows 
