34 



INSECTIVOKA 



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Sorex aratuu-s. Anterior 

 teeth in profile. X 5. 



and posterior borders sub-equal, slightly longer than anterior 



border. Cusp rounded on antero-external face, squarely truncate 



postero-internally along line connecting antero-internal and 

 postero-external corners of crown. The 

 region behind this line is occupied by a 

 flattened or somewhat concave, nearly 

 horizontal crushing surface opposed 

 during mastication to second and third 

 lobes of lower incisor (1st and 2nd upper 

 unicuspids) and to points of the two 

 lower unicuspids (3rd and 4th upper 

 unicuspids). In size the first and second 

 unicuspids are sub-equal and decidedly 

 larger than third, which in turn some- 

 what exceeds fourth. Fifth still smaller 



than fourth and closely crowded between it and antero-external 



cusp of large premolar, its cusp relatively lower than in the 



other teeth of the series. First lower unicuspid essentially 



similar to first and second upper, 



but crown longer than broad and 



without distinct crushing surface. 



Second larger than first, not 



conspicuously different from it in 



general form when viewed from the 



side, but cutting edge much longer 



and better developed, distinctly 



angled behind middle, the angle 



clearly representing a rudimentary 



second cusp, and transverse portion 



behind it a second commis- 

 sure, the tooth thus contain- 

 ing the modified elements 



of one of the triangles of a 



molar. Large upper pre- 



molar with protocone 



smaller than in the first 



and second molars, though 



well developed and of 



essentially the same form ; 



paracone smaller than pro- 

 tocone, therefore much 



smaller than in first and 



second molars ; hypocone 



small but well developed ; 



posterior margin of crown 



more deeply emarginate 



than that of molars. 



Crowns of first and second molars squarish in outline, though 



somewhat wider posteriorly than anteriorly. Outer re-entrant 



angles deeper in second than in first. Protocone long and rather 



i^'- 



Fig. 9. 

 Sorex araneus. I'eetli X 10. 



