The Skeleton 57 
and neural arch, is a heavy bone shaped like a 
truncated pyramid (4); the base of the pyra- 
mid is ankylosed with the iliua:. These bones 
seem to be much thickened transverse processes, 
but since they are not completely fused with 
their respective vertebre and are said to ossify 
separately they should probably be called sacral 
ribs. The two sacral vertebree do not seem to 
be any more closely united than are any other two 
vertebree. 
The Caudal Vertebre (Fig. 16, C). These are 
characterized by the entire absence of ribs, and 
by the presence on all but the first and the last 
four or five of V-shaped chevron bones. The 
first ten or twelve of these chevron bones articulate 
chiefly with the postero-ventral ends of the centra, 
but they also articulate with the antero-ventral 
ends of the vertebra behind themselves; and as they 
are followed caudad they seem to lie directly 
below the intervertebral regions and to articulate 
equally with the vertebre before and _ behind. 
The chevron bones gradually diminish in size 
from before back. The neural processes of the 
first four or five caudals are broad, like those of the 
more anterior regions, but caudad to this point they 
‘become narrower and more pointed, though they 
retain the same height until about the last ten or 
twelve vertebre. Towards the tip of the tail the 
dorsal spines diminish in height and finally dis- 
appear. The transverse processes of the first five 
