902 RODENTIA 



upper border rising at middle to form a slight but evident angle 

 marking hinder margin of orbit, its anterior extremity wedged 

 between lachrymal and zygomatic process of maxillary ; anteorbital 

 foramen small and slit-like, a little in front of level of anterior 

 premolar, its outer border strongly concave, its lower extremity 

 marked by a short abruptly projecting process. Rostrum forming 

 about one-third length of skull, its base rather broad, its anterior 

 region narrow and compressed, the least depth behind incisors 

 decidedly greater than width at same region ; nasals rather short, 

 moderately narrowed posteriorly, their squarely truncate hinder 

 border lying at level of extreme anterior edge of zygomatic root, 

 the broadly expanded nasal branches of premaxillaries usually 

 extending somewhat further back. Palate moderately wide, 

 slightly concave antero-posteriorly, rather noticeably concave 

 laterally between tooth-rows ; incisive foramina small, lying 

 entirely in premaxillaries, their length barely more than one- 

 third that of diastema and much less than least width of rostrum, 

 their anterior extremities very narrow ; posteriorly the palate 

 extends a little beyond level of last molar, its border truncate 

 or convex, never with median spine ; a conspicuous foramen or 

 notch at outer edge of palate behind alveolus of m 3 ; mesop- 

 terygoid space less than twice as long as wide, its lateral borders 

 nearly parallel except posteriorly, where the hamulars curve 

 rather noticeably outward ; ectopterygoid slightly developed and 

 inconspicuous. Mandible robust, the ramus deep and noticeably 

 compressed in front of tooth-row ; coronoid process broad at base, 

 tapering rapidly to an acute recurved point a little above level 

 of condyle, its anterior border moderately convex ; articular 

 process with shallow but noticeable concavity on outer surface ; 

 angular process well defined by the deep curve of its lower 

 border. 



Teeth. — Upper incisor robust, but course of shaft not con- 

 spicuously marked on side of rostrum, and root producing no 

 visible protuberance ; shaft strongly compressed, its cross section 

 elliptical in outline, flattened in front, the enamel very thin, 

 extending backward slightly on both outer and inner side, and 

 covering less than one-third circumference of tooth, its surface 

 finely pitted, yellow ; lower incisor with root extending into 

 ascending portion of ramus and forming a slight protuberance 

 on outer surface a little above level of crowns of molars, its shaft 

 much more compressed than that of upper tooth, its outline 

 ovate, narrowest in front, the enamel confined to narrow anterior 

 surface. Anterior upper premolar a simple terete spike about 

 as large as anterior outer root of succeeding tooth, its crown 

 when unworn with slightly developed anterior tubercle and 

 posterior depression, the area of crown barely more than one- 

 tenth that of jjm 4 . Molariform teeth resembling each other in 

 general size and form, each with two roots on outer side and a 

 single larger root on inner side, the inner border of crown formed 



