NO. losn. THE FOSSfL CJEXUS PTILODUS—OIDLEY. gX9 



and ridges of its sides at right angles to the horizontal plane of the 

 tooth row, and consequently in line with the direction of force brought 

 to bear on the tooth in normal use. This position of the tootli in the 

 jaAV would explain the relatively large size of tlie anterior fang, which 

 much exceeds the posterior one, since much the greater part of the 

 strain would thus be transmitted to that portion of the tooth. It 

 jjrobably also accounts for the uniform persistence of the vestigial 

 ji.j, as the latter is placed well under the anterior edge of p^ in such 

 a position as to receive part of the strain imparted to p^. Thus p. 

 evidently served as a prop or supplementar}^ buttress for the large 

 cutting tooth. 



The combined length of the two lower molars is somewhat less than 

 that of the upper true molars Avhicli they directly oppose ; but this 

 discrepancy in length is compensated by the peculiar fore-and-aft 

 movement of the jaw in chewing. Both molars are low-crowned, 

 wdth tAvo row^s of subequal tubercules. M^ has 5 cusps in the outer 

 and -i in the inner row, while m._, has 3 in the outer and 2 in the 

 inner row. M„ is broader and shorter than m^. 



The sJi-uJl is relatively short and broad, its greatest width being 

 across the posterior ends of the zygomatic arches. The zygomatic 

 arch is moderately slender. It joins the maxillary opposite the an- 

 terior half of p* and extends backward nearly to the lambdoidal 

 crest. The malar extends backward to the glenoid surface, and ap- 

 parently joins the lachrymal bone anteriorly as in the living mar- 

 supials. The anterior extension of the malar, how^ever, can not be 

 made out with certainty, owing to the almost complete obliteration 

 of suture lines in this region. The occiput extends but slightly be- 

 yond the i^osterior root of the zygoma ; this, with the extreme back- 

 ward extension of the cheek-teeth series, gives the basi-cranial region 

 very short and broad i^roportions. The brain case is large, but com- 

 paratively smaller than that of living marsupials, and is marked 

 anteriorly by a distinct but broad constriction of the skull. The 

 nasals are relatively large and broad, expanding posteriorly. They 

 join the frontals on a line slightly forward of the anterior margin 

 of the orbits. The maxillaries are relatively very large and deep, 

 and extend well backward to accommodate the long row of cheek 

 teeth. The premaxillaries are short and widely separated from the 

 frontals by the ascending portion of the maxillary. The relatively 

 broad, high-arched palate is perforated by two pairs of foramena. 

 The i:)Osterior pair are very large, occupying nearly one-half the 

 entire length of the palate. The palate back of the muzzle is narrow- 

 est between the last pair of molars and widest between the third pair 

 of premolars. The characters of the basicranial region can not be 

 made out clearly, owing to crushing and breaking, but there appears 

 to be an alisphenoid canal and a well-developed alisphenoid bulla. 



