164 —— Cincinnatt Society of Natural Hitstory. 
places it is with difficulty that the line of union can be traced. In 
this respect it closely resembles “dev, where the fusion is for half 
the length of the bones. The shaft of the tibia, above its junction 
with the fibula, is distinctly three-sided, and is bent so as to present 
a convexity, forward. For about the lower third it is so bent as to 
have the convexity backward, and a very decided concavity in 
front, owing to the greater enlargement of the lower extremity for- 
ward and inward. 
-Further, as to the upper portion, there is a broad convex side 
(broadest at the summit and narrowing downward), which looks 
forward and inward. ‘nis face is bounded exteriorly by the very 
prominent crest, which is the border of a stout blade curving out- 
ward. ‘The outer side is broadly and deeply concave, the trough 
bounded anteriorly by the crest above named, and posteriorly by 
another blade which extends from the external tuberosity to the 
point where the tibia and fibula unite. The posterior, the nar- 
rowest side, is also quite concave. 
The external tuberosity is very prominent, reaching outward and 
backward, where it is supported by the relatively broad head of the 
small fibula. The fibula below is proportionally smaller than in 
Castor, but proportionally larger above. The upper end was 
doubtless capped with the large epiphysis, with its external hooked 
spur as seen in allied genera. The external malleolus bears 
somewhat inward, so as to make a bearing with the outer articu- 
lating surface of the astragalus. 

Fig. 24.—One-third natural size Parts belonging to left hind foot: a, astragulus, 
resting on (c) caleaneum; v,-yvacancy, absence of cuboid; m, fourth metatarsal; 1, 2, 
first and second joints of fourth digit: d, deformed joint. 
Of the hind feet we have, on the right, the astragalus, the five 
metatarsals, and the first phalanx of the third digit. Of the 
left foot we have the astragalus, calcaneum, the I, III, IV and 
V metatarsals, the first phalanx of the third digit, and the first 
and second of the fourth digit. 
In no part is the detailed correspondence of structure between 
