OSTEOLOGY OF POLYGLYPHANODON—GILMORE Aa 
lated with the vertebrae, while 6 posterior ribs of the right side were 
found in such relationship as to be directly attributable to their 
proper places in the series. 
The most anterior rib to be considered thoracic is articulated with 
the seventh vertebra in both specimens. It is thought to be the first 
rib to be connected with the sternum. It is on the basis of this evi- 
dence that the anterior six vertebrae are regarded as constituting the 
complete cervical series. 
All the ribs are slender, single-headed, and curved gently nearly 
in one plane. On the anterior face of the proximal third of the 
anterior ribs is a longitudinal ridge that becomes progressively less 
and less pronounced but nowhere does this ridge overhang as in the 
cervicals. The posterior face for one-fourth of the length near the 
proximal end is traversed by a longitudinal groove. The ribs increase 
in length from the first to the thirteenth, and posterior to the thirteenth 
they shorten progressively. The length (in millimeters) of the com- 
plete ribs of specimen U.S.N.M. No. 15816 are as follows: First, 36; 
second, 41.6; third, 45; fifth, 55; eighth, 69; ninth, 71; tenth, 71; 
eleventh, 71, twelfth, 72.5; thirteenth, 74; fourteenth, 72.9; fifteenth, 
62.4; twenty-third, 14.5. 
The posterior ribs have nearly straight shafts, and there is a grad- 
ual reduction in size of the head from front to back. This reduc- 
tion in the size of the head is in conformity with the diminution 
in size of the costal facets of the vertebrae. In the type the twenty- 
third or last rib is completely preserved in situ and has a greatest 
length of 12.5 m. 
Thoracic ribs 9 and 10 of specimen U.S.N.M. No. 15816 show an 
exostosis of the bone on their upper thirds, suggesting that they had 
suffered injury and had healed in life. At the ends of several of the 
median ribs are ossifications that suggest strongly the presence of 
ossified sternal ribs. These may be plainly seen in plate 25. 
PECTORAL GIRDLE 
The ossified pectoral girdle is composed of the scapula, coracoid, 
clavicle, and interclavicle. Parts of the girdle are present in all 
the better-preserved specimens. 
Scapula-coracoid.—The right scapula-coracoid of specimen U.S.N.M. 
No. 15559 is nearly complete, as shown in figure 27, and the detailed 
description to follow is based on this bone. The scapula is relatively 
broad and heavy for its length. The upper end is expanded, with a 
truncated end that is slightly convex anteroposteriorly. The missing 
portion of the end has been restored after specimen U.S.N.M. No. 
15818. A small portion of the ossified suprascapula remains attached 
to this end, as shown in figure 27, sse. The sinuous posterior border 
is thickened and rounded throughout the greater part of its length; 
