RODENTIA SCItTRINAE SCIURUS. 243 



SCIURUS, Linnaeus. 



Sciurus, LINNAEUS, "Systema Naturae, 1735." 



Incisors compressed. Ears long; snout and upper lip divided; tail long, nearly equalling the body, or even exceeding it in 

 length, with long bristly hairs arranged chiefly on the sides. No cheek pouches nor extension of the skin along the sides. Inner 

 lines of the upper molars parallel. Anterior upper molar very rudimentary or wanting. No dorsal black stripes. 



This genus comprehends a large number of species, the most highly organized of which 

 appear to occupy the chief rank among Rodentia. They are quite generally distributed, most 

 abundantly in North America, although the largest species occur in the Old World. South 

 America possesses comparatively few, its vast forests counting up scarcely more than half a 

 dozen species. 



The principal peculiarities of the skeleton, as shared by other genera, have already been 

 adverted to. The cranium, however, has a very great development, and the edges of the frontal 

 bone extend far over the orbits. The post-orbital processes are acute and have a considerable 

 bend downwards. The snout is long and tapers gently to the tip; the nasal bones do not reach 

 back to the line of the malars. They are narrowed behind, and are not more than half as wide 

 as the upper faces of the nasal processes of the intermaxillary. The section of the nose is quad 

 rilateral and sub-wedge-shaped, deeper than broad, and narrower below. The ante-orbital 

 foramen is a very narrow vertical slit, situated about midway between the molars and the incisive 

 foramina. The upper molars are normally five, although the first is always rudimentary, and 

 sometimes entirely wanting in the adult. The second, third, and fourth molars increase 

 gradually in width and are quadrangular ; the fifth, a little less than the fourth, is sub-trian 

 gular, the anterior and exterior edges nearly straight and at right angles,, the postero-internal 

 rounded, (the reverse of Cynomys). The line of the molars is less than one-fifth the total 

 length of the skull, their inner margins very slightly divergent anteriorly. The posterior end 

 of the incisive foramen is about midway between the second molars and the incisors. The 

 incisors are much compressed ; twice as deep as broad, with very little of the colored enamel 

 visible from the sides. 



Compared with Otospermophilus the skull of Sciurus differs in being narrower, with the sides 

 more vertical, and the cranium more capacious; the muzzle is longer; the nasal bones narrower 

 behind ; the frontal bone is broader between the ante-orbital notches and behind the post-orbital 

 processes, which are less highly developed. The malar bone is narrower, thinner, and more 

 vertical ; its middle part is much deeper, projecting above and below, so that the continuity of 

 outline is interrupted by an angular process, instead of the margins being parallel throughout. 

 The ante-orbital foramen is much more anterior, as well as the tubercle behind it. The molars 

 are much smaller, inserted less obliquely, and occupy less space in the skull. The first molar 

 is always rudimentary, instead of being moderate in size, with a distinct ridge. The incisors 

 are narrower, deeper, and the sides more parallel. 



The other points of difference are the smaller feet and claws, usually longer and bushier tail, 

 absence of cheek pouches, &c. 



In the large number of species belonging to the genus Sciurus there may be recognized two 

 distinct types: that of the large squirrels with elongated muzzle, very long bushy tail, and 



