166 THE DESEADO FORMATION OF PATAGONIA 
of each crest is ground down; so that instead of the crown 
wearing to a level surface, it retains throughout life two 
oblique grinding surfaces. 
The lower dentition is more reduced than the upper. 
When in position, the tips of the two lower tushes diverge, 
so as to come in contact with the tips of the second upper 
tushes, from which I conclude that the lower tush is the 
second, rather than the first incisor, the latter having been 
lost when the second became enlarged as was the case in 
elephants. This lower tush has the same oval cross sec- 
tion, enamel on the front face only, and beveled tip as the 
corresponding upper incisor; but, in the same individual, 
is somewhat longer and slenderer. When isolated, how- 
ever, it is difficult to tell whether one is handling a small 
upper tush or a larger lower one. 
The remaining incisors, the canine, the first and the 
second premolars are wanting, and their place is taken by 
a small diastema. ‘The lower premolars and the molars 
are similar to those of the upper jaw, except the cingulum 
is on the posterior margin, and the wear is on the posterior 
face of each transverse crest. 
The skull is very long and narrow, with wide and deep 
zygomatic arches. ‘The nasal opening is moved back 
from the front of the snout to just opposite the orbit, 
leaving a long, narrow, but heavy snout, made up mostly 
of the premaxillae, on the anterior end of which is an oval 
boss, which must have served as an attachment for muscles. 
With the tushes developed so as to bite against each other, 
as in a gnawing animal, I can not see any possibility for 
the development of a pendant proboscis, but think that the 
snout must have been developed more like that of a pig, 
but probably to a greater degree. ‘The premaxillae are 
long and heavy, and prolonged backward to contain the 
roots of the great tushes; but these bones are not developed 
on the palatal side of the snout at all. The maxillae 
are also massive, carrying the premolars and molars, 
