SCOTT: TOXODONTA OF THE SANTA CRUZ BEDS. 165 
shows, these likenesses are due merely to the mechanical readjustments 
necessitated by the greatly augmented bulk and weight. 
The femur of Nesodon (PI. XXIII, figs, i, 2) is much more perissodactyl 
in character than is that of Toxodon; it is of moderate length, a little 
shorter than the humerus, though the effective length, measured from the 
head to the condyles, is slightly greater than that of the humerus. The 
head is oval, with the long axis transverse, and is set upon a distinct 
neck ; the moderately large, though shallow, pit for the round ligament is 
placed upon the posterior aspect of the head, so as to be invisible in front 
view. A deep notch separates the head from the great trochanter, which 
is thick, massive and rugose, but low, not rising quite to the level of the 
head ; the digital fossa is fairly deep, but small, and the prominent linea 
intertrochanterica is short, not extending to the second trochanter. The 
latter is a long and moderately prominent ridge, which arises a short dis- 
tance below the head. The third trochanter is very conspicuous and is 
placed a little above the middle of the shalt. 
The proximal portion of the shaft is broad and antero-posteriorly com- 
pressed, becoming more rounded and transversely oval in section down- 
ward ; the posterior surface of the shaft is nearly smooth, owing to the 
absence of any distinct lineae asperae, but near the distal end there is a 
well-defined pit for the plantaris muscle, though the depth and distinct- 
ness of this pit vary much in different individuals. The rotular groove, 
which projects prominently in front of the shaft, is broad, shallow and 
asymmetrical, which is due to the greater thickness and prominence of 
the internal portion. Distally, its articular surface is continuous with the 
inner condyle, but separated by a narrow space from the outer; there is 
no definite suprapatellar fossa. The condyles are rather small and do not 
project strongly behind the plane of the shaft ; there is considerable in- 
equality in size between them, the inner one being broader and flatter, 
the outer one narrower and more convex. The external epicondyle is 
quite prominent and heavy, the internal one very much smaller. 
Like the pelvis, the femur of Toxodon is greatly modified from the con- 
dition in Nesodon and bears considerable resemblance to that of the ele- 
phant. It is relatively elongate and is much the longest of all the limb- 
bones ; the head is more hemispherical than in the Santa Cruz genus 
and the pit for the round ligament is merely a vestige, a shallow, trian- 
gular area, which emarginates the articular surface on the posterior side 
