244 PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 92 
VERTEBRAE 
The vertebral column is represented by relatively long articulated 
series in 4 of the 12 known individuals, besides a considerable number 
of short series and separate vertebrae belonging to other specimens. 
From a study of all, most of the column is known except the distal 
half of the tail. 
All the vertebrae are procoelous. The vertebral column is best 
represented in specimen U.S.N.M. No. 15816 (see pl. 25), which has 
39 articulated vertebrae present. Twenty-nine of these are presacral, 
two sacral, and eight anterior caudals. Beginning with the atlas, 11 
are articulated in series. A short gap separates the eleventh and thir- 
teenth, but posterior to this interval they form a continuous series 
ending with the eighth caudal. That the twelfth vertebra is missing 
is indicated by the presence in sequential position of parts of both ribs 
that formerly articulated with it, as shown in plate 25. 
In view of the little disturbed condition of the vertebrae with 
practically all the ribs in articulated position, it would appear that 29 
represents the complete presacral series. A skeleton of /guana, in 
comparison, has 24 presacral vertebrae. 
How many of these are to be designated cervical depends entirely 
on how the count is made. Most authorities regard all vertebrae 
whose ribs attain a connection with the sternum as belonging to the 
dorsal series. This criterion, however, is of little practical use with 
fossil specimens, since the evidence of such a connection is seldom 
preserved. In the present specimen the spinous processes undergo a 
distinct change on the ninth vertebra, and this may indicate the point 
of division between cervical and dorsal. If so, there would be 8 
cervicals and 21 dorsals, but the presence of long ribs articulated 
with the seventh and eighth vertebrae in specimens U.S.N.M. Nos. 
15816 and 15566 appears to indicate adequately that these vertebrae 
were attached to the sternum as in 7guana and are therefore dorsal. 
There are no lumbars, for the last presacral bears a short rib, as 
shown by three specimens. 
The sacrum is composed of two noncoalesced vertebrae, as shown 
by the type and by U.S.N.M. Nos. 15566 and 15816. 
The total number of caudal vertebrae cannot be determined from 
available specimens. Specimen U.S.N.M. No. 15817 (see plate 25) 
has a series of 19 vertebrae of the anterior portion of the tail, articu- 
lated in series with the sacrals, and when these are compared with 
those of an Jguana of the same size they appear to indicate a tail 
of about equal length and proportions. The restoration in plate 
26 has been given 48 vertebrae in the tail, with a total length of about 
18 inches. 
The vertebral formula of Polyglyphanodon sternbergi, as known at 
this time, may be stated as C-6; D-23; S-2: CD (48+). 
