Family SCIURID^. 



The family Sciuridee, as now commonly restricted, may be characterized 

 as follows: Dental formula; I. £1; Pm. |5f or j^; M. |=| = |f or H. 



Grinding-teeth rooted, with, during youth, tuberculated crowns ; the tubercles 

 soon becoming much modified or obliterated by attrition, generally giving 

 rise for a time to transverse ridges. The first upper premolar, when two are 

 present, is often minute, and is generally much smaller than the second. In 

 strictly congeneric species, in Sciurus and Tamias, the premolars may be 

 either two or one. Occasionally two are present in species that have usually 

 only one. In species having a single premolar, a second deciduous premolar 

 is generally assumed to have been present during early life, but to this there 

 are frequent exceptions. The first upper premolar, when two are present, 

 is always single-rooted, with a simple pointed crown, and is often so minute as 

 to be apparently functionless. The other upper grinding-teeth are triple- 

 rooted. The lower premolar is double-rooted, the last lower molar generally 

 triple-rooted, and the others quadruple-rooted. 



The skull varies considerably in form, from the short, broad skull of the 

 arboreal Squirrels to the narrow, very much elongated skull of some of the 

 Spermophiles. There is a well developed postorbital process, which may be 

 either short, pointed, and triangular, or long, slender, and much decurved. 

 The infraorbital foramen is small, and placed considerably in advance of the 

 zygomatic process of the maxillary (usually about midway between the ante- 

 rior premolar and the maxillo-intermaxillary suture), and varies from a nar- 

 row vertical slit to an oval or triangular opening. The palate is very broad 

 and flat, and extends posteriorly considerably beyond the last molar (except 

 in some exotic species), and forms a continuous uniform plane. Molar series 

 parallel. Feet scansorial or fossorial. Tail long or short, terete and slender 

 or bushy and distichous, always well haired. Body generally elongate, 



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