SCIURUS 



687 



section. The cheek-teeth are tubercular, brachyodont, and 

 rooted. In the upper jaw, the anterior premolar (/*) is very 

 small and simple, and has little functional importance ; the 

 other teeth {p^ — m^) are subtriangular in form and have two 

 low rounded tubercles (4 and 5), each supported by a slender 

 root, on their outer borders ; with these tubercles are more or 

 less evident traces of the cusps i, 2 and 3 ; on the inner side of 

 each tooth is a single relatively 

 lofty cusp, formed by the fusion of 

 at least three elements, and sup- 

 ported by a long and stout root ; 

 the base of this inner cusp is con- 

 nected by low transverse ridges with 

 the bases of the outer cusp 4 and 

 5 ; and these transverse ridges 

 form the forward and backward 

 margins of a spacious and rather 

 deep central valley. The lower 

 cheek-teeth (J>i — m^ are quadratic 

 and four-rooted ; each has two 

 low rounded tubercles on the outer 

 side ; a shallow basin-shaped con- 

 cavity occupies the greater part of the surface of the crown ; 

 the inner margin of the basin is crenulate behind but anteriorly 

 it rises up into a lofty terete cusp. When the teeth are fitted 

 together, the prominent inner cusp of each upper molar is seen 

 to work in the basin-shaped concavity of the opposing lower 

 tooth like a pestle in a mortar ; while the lofty antero-internal 

 cusp of each lower molar shears within and between the internal 

 cusps of two contiguous upper molars. As explained by 

 Forsyth Major {Proc. Zool. Sgc, 1893, 181), squirrels with 

 cheek-teeth like those of Sciurus may be regarded as represent- 

 ing, in the molar evolution of the Sciuridce, an intermediate 

 stage, which connects the most brachyodont forms {e.g., the 

 Eocene S. spectabilis, Major, the living Reithrosciurus of 

 Borneo and Protoxerus of Africa) with the most hypsodont 

 groups (the Ethiopian Xerus group, and the Oriental Menetes 

 and Rhinosciurus). 



Fig. 98. — Cheek-Teeth of 

 Squirrel {Sciurus vulgaris). x 5. 

 Reproduced from Miller's Catalogue, 

 by permission of the Trustees of the 

 British Museum (Nat. Hist.). 



