532 LAND MAMMALS IN THE WESTERN HEMISPHERE 



inner and outer faces, but quite thin transversely, and with 

 finely serrate posterior edge. It is difficult to understand 

 how these great tusks, which would seem to have blocked 

 the entrance to the mouth, could have been effectively used, 

 unless the creature could open its mouth much more 

 widely than any existing mammal, so as to clear the points of 

 the tusks, and would then strike with them as a snake does 

 with its fangs. There are great anatomical difficulties in 

 the way of accepting this explanation and the problem, 

 which is the same as that presented by the juintatheres 

 (p. 446), is still unsolved. It is, however, quite certain that 

 no arrangement which was disadvantageous, or even in- 

 efficient, could have 

 persisted for such vast 

 periods of time. The 

 y lower canine was 

 much diminished and 



Fig. 262. — Upper teeth of ^Smilodon, left side. P. 4, hardly larger than an 

 fourth premolar. m. 1, first molar. (After incisor. The tWO 

 Matthew.) , 



upper premolars were 

 the third and fourth of the original series ; the third was small, 

 but the fourth, the sectorial, was a very large and efficient 

 shearing blade. In addition to the two external trenchant 

 cusps of the blade, which are present in the Carnivora gener- 

 ally, the cats have a third small, anterior cusp which in ^Smilo- 

 don was large ; the internal cusp had almost disappeared. The 

 single upper molar was very small and so overlapped by the 

 great carnassial as to be invisible from the side. The third 

 lower premolar was small and unimportant and most speci- 

 mens had lost it, leaving only the fourth, which was larger 

 and evidently of functional value. The single molar was the 

 sectorial, a large, thin, flattened blade, consisting of only two 

 cusps, one behind the other, the trenchant edges of which met 

 at nearly a right angle, and there was no trace of a heel. 



The skull was in appearance closely similar to that of 



