SCOTT: TOXODONTA OF THE SANTA CRUZ BEDS. 1 67 
flat and there is no pit for the plantaris muscle. The rotular trochlea 
differs from that of Nesodon in being broader, shallower and more asym- 
metrical, owing to the greater thickness of the internal portion, which is 
very broad and prominent and has the articular surface reflected over 
Fig. 30. 
Nesodon imbricatus : A, left femur, dorsum; B, the same, external view. Also left patella, 
dorsum. All figures X i- 
upon the internal side. The condyles are of more nearly equal size and 
similar shape than in Nesodon and are more nearly approximated, 
making the intercondylar fossa much narrower. Both condyles are sep- 
arated by narrow spaces from the articular surface of the rotular groove. 
That the great changes in the character of the femur between the Santa 
Cruz and the Pampean genus should be chiefly ascribed to the great 
increase in the weight of the latter animal, is made probable by the same 
considerations as in the case of the pelvis. Similar changes may be fol- 
lowed out in other phyla, notably in the Titanotheriidse and the Ambly- 
poda. In the late and well-nigh gigantic species of the latter group the 
femur has become most deceptively proboscidean in character. In each 
of the four phyla the modifications of the femur are as follows : ( i ) The 
pit for the round ligament is greatly diminished in size or altogether lost ; 
(2) the great trochanter becomes very thick and heavy, but its proximo- 
distal height is diminished ; (3) the third trochanter is greatly reduced or 
