562 
UNGULATES. 
rhinocerotic type, and lacking the marked curvature of the crown characterising 
those of the toxodonts. The vertebrae of the neck are comparatively short, with 
flattened articular surfaces, and the lateral canal piercing the transverse process in 
the ordinary manner. The wrist and ankle-joints were probably of the linear 
type; the calcaneum articulated largely with the fibula; and the astragalus was 
quite flat, and furnished with a large head for articulation with the navicular bone. 
The femur, when known, had a large third trochanter. 
In both families the upper cheek-teeth were of a rhinocerotic type of structure, 
having a continuous external wall undivided into lobes. The group is widely 
distinguished from the Amblypoda by the structure of the cheek-teeth, and not 
improbably by the number of digits having been three in place of five. It is, 
however, decidedly the most generalised of the three South American extinct 
suborders, as is especially shown by the flattened astragalus. The remarkable 
similarity of the molars of 
Astranotherium to those of 
rhinoceroses must probably 
be considered as largely due 
to parallelism, since the 
structure of the ankle in 
the allied Homalodonto- 
tlierium indicates that the 
group diverged from the 
common ancestor before the 
modern Odd-toed Ungulates 
had acquired their charac¬ 
teristic foot-structure. 
In the homalodonto- 
tliere, representing the first 
family, the teeth, as shown 
in the accompanying figure, 
comprise the full number of 
i §, cj, 2 ) 4 > and have 
no gap; the canines being 
rooted and of relatively 
small size, and the molars 
with comparatively short 
crowns. The upper pre¬ 
molars are nearly as complex as the molars; and the third upper molar is not 
very markedly different from the two preceding teeth. The lower molars are 
in the form of double crescents, of which the anterior develops a loop like 
that found in the horses. It is stated that the toes terminated in claws. The 
one known species of the genus was an animal of the approximate size of the 
Sumatran rhinoceros. 
The gigantic astrapothere, which alone represents the second family, differs 
from the last genus by the more specialised and reduced dentition, the enlarged 
teeth of each jaw taking the form of permanently growing tusks, which are worn 
