10K TOXODON AND NESODON 215 
the free end of the nasals, which may be related to the presence 
of a short proboscis. The zygomatic arch is strong and_ broad ; 
the mandibles are provided with a long symphysis. The dental 
formula is 12 C®;1 Pm,4, M3. The teeth are prismatic and 
hypselodont, growing from persistent pulps. The molar teeth are 
slightly arched in form, whence the name of Zoawodon, “ bow teeth.” 
The strong chisel-shaped incisors suggest the Rodents and Hyraz. 
The cheek teeth, moreover, are by no means unlike those of Rodents 
in their pattern. They are at any rate not at all like those of ex- 
isting Ungulates. The small size of the canine and of the first pre- 
molar produces a diastema in the tooth series. The sacrum consists 
of five vertebrae, and the ischium does not articulate with it. 
The shoulder blade has a strong spine, but only a rudimentary 
acromion ; nor is the coracoid well developed. The radius crosses 
the ulna, as in the Elephant ; the whole fore-lmb is shorter than 
the hind-limb, which must have exaggerated the hang-dog ex- 
pression of the creature when alive. The elements of the carpus 
interlock in the modern fashion. Those of the tarsus, however, 
are primitive in lying below each other without alternation. The 
carpus has a centrale. The fibula articulates with the calcaneum. 
The femur has no third trochanter. There are three toes to all 
the limbs. It is clear that this assemblage of characters will not 
allow the placing of Zoxodon in any living Ungulate order. If 
the middle toes appear by their slight pre-eminence to approach 
the Perissodactyle form, the peculiar surface contour of the molar 
teeth, letting alone the absence of a third trochanter on the femur, 
will not permit this classification. 
Allied to Zoxodon is the genus Nesodon. It was so named 
from an “island lobe” on the inner side of the upper molars. 
This creature, smaller than Zoxvodon, also differs from it in the 
fact that the dentition is complete, and in the pattern of the 
molars, which is rather more complex. There is still the slight 
projection upon the premaxillary bones, but the nostril is directed 
more forwards than in Joxodon. The zygoma, too, 1s massive. 
The second pair of incisors in the upper jaw and the outer (third) 
pair in the lower jaw form biggish tusks in the adult. These and 
the molar teeth are, however, finally rooted, and do not grow, as in 
Toxodon, from persistent pulps. The genus is from the older 
Tertiary of Patagonia. Five or six species have been described. 
Some are as large as a Rhinoceros, others as small as a Sheep. 
