IAS PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 92 
into the centrum at the constriction for the ball. Below this ridge 
the side of the centrum is slightly hollowed out, this feature being 
most prominently developed in the anterior half of the series and 
tending to fade out in the direction of the sacrum. Above this ridge 
and between it and the less conspicuous ridge joining the prezyga- 
pophyses and postzygapophyses there is a slight excavation of the 
surface that widens posteriorly. 
Anteriorly the diapophyses stand out prominently from the sides 
of the centra and are about equally supported by the centra and 
neuropophyses. ‘The costal facets for the ribs on the anterior dorsals 
are subovate, with the longer diameter nearly vertical (see fig. 24). 
These facets gradually increase in size on the first five dorsals, remain 
subequal on the next three, and, beginning with the ninth or tenth, 
are progressively reduced in size and changed in outline from oval 
to semicircular (see fig. 25). A small zygosphene-zygantrum articu- 
lation is developed on all the dorsals (fig. 24). These are more fully 
functional than the rudimentary stage found in the varanid lizard 
Saniwa. 
Ficure 25.—Posterior dorsal vertebra of Polyglyphanodon sternbergi Gilmore, U.S.N.M. 
No. 15477, type, natural size: A, Lateral view; B, ventral view; C, anterior view; spine 
largely missing. 
Measured along the top the 23 dorsal vertebrae in specimen U.S.N.M. 
No. 15816 have a total length of about 350 mm. 
Sacral vertebrae.—The sacrum consists of two vertebrae, and in none 
of the specimens is there indication of coalescence. The anterior sacral 
is slightly stouter than the posterior one and bears the heaviest sacral 
rib, These ribs are attached to the anterior two-thirds of the sides of 
the centra, their ventral surfaces being only slightly above the ventral 
level of the centra (see fig. 26). The ribs in all available specimens are 
completely coalesced, with no trace of their sutural union with the 
centrum. 
Seen from below, the sacral centra are broadly rounded transversely 
and provided with the usual cup and ball. The spines are narrowed 
anteroposteriorly as contrasted with the wide spinous processes of the 
dorsals. Both vertebrae are provided with zygosphene-zygantrum 
articulation in addition to the regular zygapophyses. 
The sacral ribs are long, the rib of the first sacral projecting straight 
outward from the centrum, the rib of the second outward and forward, 
as shown in figure 26. The ventral surface of the second is indented 
