OSTEOLOGY OF POLYGLYPHANODON—GILMORE 261 
Fibula—tThe fibula, although a slender bone, is stouter than that of 
an Zguana of corresponding size. It is distinctly longer than the 
tibia, and the planes of the two ends are slightly twisted with respect 
to one another about the longitudinal axis. Both ends are truncate 
diagonally to the longer-diameter of the shaft. The proximal end is 
the most expanded, with a swelling out of the anterior border into a 
thin lip that turns inward. The upper articular surface is long and 
narrow and turns strongly downward on the inner side for articulation 
with the condyle of the femur. On the external side at the proximal 
end a rounded slightly raised projection marks the point of insertion 
of a ligament (see fig. 35). The distal end is little expanded antero- 
posteriorly but is thickened transversely. The articular end is con- 
vex, the articular surface extending upward on the internal side. In 
cross section the shaft is subovate in outline. 
Measurements of right fibula of U.S.N.M. No. 15477 (in millimeters) 
Greatest length es ee NT ee Re OOO 
Greatest: widthror proxam alien 2 ee ee ee ee ee eee ey vale re 
Grestestiwidthiot distalzen cles 0s) us re eee eh ee 10.0 
east diameterof shatt-at midleneth==— 2. Soe eee ae 3. 4 
Hind foot—The structure of the hind foot is best illustrated by the 
left pes of specimen U.S.N.M. No. 15817, which has every bone present 
in articulated order, as shown in plate 25. Unfortunately the tarsus 
can be only partly exposed. This individual is the largest of any of the 
specimens now available; the femur measures 88 mm. in length as 
contrasted with 72.8 mm., the length of the femur of the type specimen. 
The hind foot illustrated in figure 36 is a composite based upon the 
hind feet of specimen U.S.N.M. No. 15568 preserved in nearly articu- 
lated position. Elements that are missing in one foot are usually 
present in the other, so that by a study of both it has been possible 
to determine the complete composition of the pes. The correctness 
of this restoration of the hind foot is now fully verified by the com- 
plete left pes of U.S.N.M. No. 15817, shown in plate 25, which came to 
hand after the drawing had been completed. 
Unfortunately both tarsi were in a disturbed state and their com- 
plete structure is therefore rendered uncertain, a remark that applies 
equally well to specimens U.S.N.M. Nos. 15816 and 15817, shown in 
plate 25. It is for that reason that no attempt has been made to re- 
store the complete tarsus in figure 36 further than illustrating those 
elements about whose identity there can be no doubt. 
The tarsus consists of not less than six, possibly seven, bony ele- 
ments. The proximal row consisting of the coalesced astragulus and 
caleaneum. These blocklike bones are so completely fused that their 
exact line of separation is difficult of detection. 
The astragulus or tibiale plus intermedium is subquadrangular in 
shape when viewed from the front. The tibial articular surface is 
