SCIURUS 901. 



convex to region between postorbital processes, then abruptly 

 and strongly convex over greater portion of brain-case to a slight 

 but evident concavity immediately in front of lambdoid region ; 

 ventral profile somewhat parallel to dorsal profile in general 

 direction, but diverging slightly in its anterior half and con- 

 verging a little posteriorly ; posterior truncation of brain-case 

 nearly vertical, slightly convex when viewed from the side, the 

 occipital condyles not visible from above. Brain-case broadly 

 ovate in outline when viewed from above, its greatest width 

 about equal to length, its width posteriorly somewhat greater 

 than that at postorbital constriction ; surface essentially smooth, 

 though in old individuals, particularly of the larger races, a low 

 ridge extends backward from base of postorbital process, across 

 middle of parietal to lambdoid region, the two ridges together 

 forming a lyrate figure ; lambdoid crest represented by a mere 

 angular ridge along course of lambdoid suture ; viewed from the 

 side the brain-case is conspicuously rounded through anterior 

 three-fourths, the low occipital region marked off from main 

 portion by a shallow but evident constriction ; occiput moderately 

 high, its depth to lower lip of foramen magnum about two- 

 thirds mastoid breadth, much exceeded by median portion of 

 l)rain-case, its dorsal and lateral margins forming an evenly 

 rounded, nearly semicircular arch ; foramen magnum wider than 

 high. ; occipital with three distinct swellings between foramen 

 magnum and lambdoid ridge, each about equal to exposed portion 

 of petrosal ; paroccipital processes small, their extremities hooked 

 inward and slightly forward, scarcely extending to level of lower 

 edge of condyle ; basioccipital rather broad and short, its width 

 in region of suture about equal to median length ; median ridge 

 slightly developed ; edge of basioccipital in region of suture 

 slightly raised, but not forming a distinct lateral process ; 

 auditory bullfe sub-circular in general outline, rather evenly 

 inflated, but with an evident antero-internal flattening, their 

 antero-posterior diameter equal to distance from front of bulla 

 to front of «!•', their lateral diameter to inner margin of meatus 

 bfirely equal to least width of basioccipital; meatus with a 

 distinct rim except along postero-upper border. Interorbital 

 region about as broad as long, its least width nearly the same 

 as postorbital constriction, its surface nearly flat, though usually 

 with a low but evident swelling at each side posteriorly, the 

 bases of postorbital processes about on level with median region ; 

 notch at anterior base of postorbital process small but well 

 developed, the orbital border sometimes complete so as to trans- 

 foi'm the notch into a foramen ; postorbital processes long, slender, 

 strongly bent downward, the orbit surrounded by bone througli 

 about three-quarters of its circumference. Zygomata not widely 

 spreading either in front or behind, the arches essentially parallel 

 with each other through tlie gi-eater part of their extent ; jugal 

 projecting posterioi'ly lj(^hind zygomatic process uf squamosal, its 



