MDS 867 



ti'iiucate ; lambdoid suture passing along anterior border of inter- 

 parietal so th.at the bone lies entirely within occipital ; '' sides 

 of brain-case abruptly rounded off or faintly angular, never 

 beaded. Occijjut broad and low when viewed from behind, but 

 central jiortion of brain-case not rising conspicuously above it ; 

 paroccipital process short and inconspicuous, barely extending to 

 level of lower lip of foramen magnum. Floor of brain-case 

 with no striking peculiarities ; width of basioccipital along 

 anterior border contained about 2^ times in median length ; 

 auditory bulla moderately large, less inflated than in Apochymiis 

 fsylvatiriis but occupying about the same area on base of skull, 

 its beak rather short and broad, but evident, the meatus with 

 anterior portion of upper border slightly projecting. Tnter- 

 orbital region distinctly wider than rostrum, slightly convex 

 laterally, the margins falling away scjuarely but with no trace 

 of bead. Zygoma relatively heavy, compressed throughout but 

 not evidently expanded, moderately bent downward and moder- 

 ately spreading anteriorly, so that greatest zygomatic breadth is 

 usually just in front of glenoid level ; plate forming outer wall 

 of anteorbit-fil foramen well developed, its anterior border vertical, 

 abruptly rounded above ; a short but very distinct peg-like 

 process for muscle attachment at antero-inferior angle of plate, 

 this process nearly as well developed in half-grown young as in 

 adults. Rostrum slightly deeper than broad, with no special 

 peculiarities of form ; nasals truncate or bluntly pointed 

 posteriorly, extending to or slightl}' beyond lachrymal level, and 

 usually a little exceeded by nasal branches of premaxillaries. 

 Incisive foramina very long (nearly equal to diastema), extending 

 from about 1 • 5 mm. behind incisors to level of middle of crown 

 of vi^ ; their greatest width is at I'egion of maxillo-premaxillary 

 suture ; jjosteriorly they narrow to an almost acute termination, 

 a peculiarity of form highly characteristic of this group as com- 

 pared with other European Muridse. Palate extending slightly 

 behind level of m-^, its length behind incisive foramina less than 

 width including tooth-rows. Mesopterygoid space moderately 

 long, wider posteriorly than anteriorly, squarely truncate in 

 front, the pterygoids and hamulars straight, the latter barely 

 in contact with bulht*. Mandible rather short and deep as 

 compared with that of Apodentus si/lvatlcus, the coronoid process 

 well developed, strongly curved backward, its tip rising slightly 

 above level of condyle. 



Teeth. — Upper incisors much compressed, the outer and 

 inner borders nearly parallel through anterior half of their 

 extent, the transverse diameter contained about 2^^ times in 

 antero-posterior diameter. Enamel unusually thick, scarcely 

 extending backward on inner side of tooth, but folding notice- 



* In Apodemus agrarius, which has a similarly ligulate interparietal, 

 the suture passes along posterior border so that the small bone lies within 

 the parietals (fig. 168, p. 837). 



3 K 2 



