IO 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
men. The manus in Hegetotherium is unknown and the above state- 
ment regarding the degree of specialization in foot-structure displayed by 
Typothevium may, accordingly, require modification in the light of fuller 
knowledge. 
III. With the Rodentia. 
In many features of skull and skeleton the Typotheria resemble the 
rodents. This is most apparent in the specialized forms like Pachyvukhos. 
In none of the Typotheria are the following characters peculiar to rodents 
developed : 
1. Persistently growing, chisel-shaped incisors (If of the permanent 
series, Weber, 1904, p. 480). If of the permanent series is enlarged in 
some of the Typotheria and may grow persistently, but is modified for 
cropping and not for gnawing. 
2. More or less antero-posterior elongation of the mandibular condyle 
and corresponding modification of the glenoid fossa to permit backward 
and forward movement of the mandible. In the Typotheria the condyle 
is transversely extended, approximately circular in outline, with the glenoid 
surface flattened, and the movement of the mandible is from side to side. 
3. Frequent outward curvature of the crowns of the upper molars and 
inward curvature of those of the inferior series in hypsodont forms. The 
reverse is true in the Typotheria. 
4. Contact of ascending process of premaxillary with frontal. This 
process is short and robust in the Typotheria and is widely separated from 
the frontal by the maxillary. 
5. Elongation of the mandibular angle. The angle is evenly convex 
in the Typotheria. 
6. The rodent astragalus is characterized by a broad, short, rather shallow 
trochlea, with the crests sharp and equally developed, distinct neck and 
flattened head, convex distally ; trochlea symmetrical to the vertical plane ; 
fibular and internal malleolar facets vertical; body limited posteriorly; 
no astragalar foramen. In the Santa Cruz Typotheria, the astragalar 
trochlea is deeper than in rodents, the crests may or may not be equally 
developed and the head is globular without antero-posterior flattening. 
The symmetry of the trochlea with respect to the vertical plane varies in 
the different families (pp. 2-3). In the other characters they resemble the 
rodents. 
7. The presence of a free centrale in the carpus in all rodents except the 
