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developed as carnassials. Their construction is essentially the same 
in Hyænodon , Pterodon and the still more primitive forms Cyno- 
hyænodon, Deltatherium etc. (Fig. 2, diagr. 4 and 5). The outer 
edge is in Pterodon curved with the concave side outwards and 
divided into four cusps of unequal size: the foremost of them is 
small and low (1), obliquely behind and inside it are two nearly 
o 
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Fig. 2. 1. Cynohyænodon cctyluxi ) p 4 -m 3 . (m 2 represented 
from the outer side). — 2. Pterodon dasyuroides, m 1 (from above 
and from the inner side). — 3. Hyænodon brachyrhynchus, 
p 4 -m 2 , (m 1 ^ 2 from above and from the outer side). 
equal cusps, the one behind the other (4 and 5), and obliquely 
outwaids behind the hindmost is a low, lengthened cusp with sharp 
edge (3). Inside the two main middle cusps the ordinary heel (6) 
is placed. It is evident from the diagram (diagr. 4) that the middle 
outer one (2) of the six cusps found in Dasyurus is wanting — 
if it has totally disappeared or, as in Sarcophilus, has joined the 
