1910.] Multituherculates are Marsupials. 169 



In reffard to the INIultituberculate dentition it seems to be sometimes 

 taken for granted that in the Plagiaulacidfe the motion of the jaw was much 

 as in the more highly specialized types of Rodents, namely decidedly antero- 

 posterior. But the mandibular condyle of Plagiaulax and Ctenacodon is 

 an elongate oval the long axis of which is strongly inclined to the plane 

 of the grinding teeth; hence the motion of the mandible must have been 

 forward and upward and then slightly backward. The large piercing lower 

 incisors, which probably fitted into prehensile-incisive upper incisors of the 

 Bolodon type, must have moved principally upward and only slightly back- 

 ward. The same conclusion is indicated by the enlarged obliciuely-grooved 

 premolar. Finally even in the moi'e highly specialized Mcniscoessus 

 (Osborn, 1907, fig. 55, p. 106) the well formed small crescents woidd require 

 and permit only a small upward and backward pull of the jaw. Apparently 

 it is chiefly in Pohjmastodon that the molar cusps become much worn down 

 at the tips (Fig. 8). 



Marsupial affinities of the Multituberculata. 



The most important discovery bearing on the genetic relations of the 

 ^Slultituberculates is that recently made by Gidley (1909) who has described 

 the skull of Ptihdus (Chirox) as being typically Marsupial in type. Thus 

 it has the inflected angle of the jaw, the fenestrated palate, the backward 

 extension of the malar into the glenoid fossa, etc. Gidley also finds that the 

 upper dentition of Plagiaulax must have been of the type represented by 

 Bolodon Owen. He concludes that the Multituherculates are Diprotodont 

 Marsupials. 



This conclusion had been reached by Falconer, Owen, Marsh, Cope, 

 Osborn and Ameghino but the evidence had always remained very incom- 

 plete. Cope (18S2. 2, p. 259), upon the discovery of the multicusped teeth 

 of Ornithorhytichus suggested that the jNIultituberculates were related to 

 the Monotremes. Confirmatory evidence that the Multituherculates are 

 Marsupials is offered by remains of Pohjmastodon taoensis in the American 

 Museum of Natural History (Fig. 8). In this Basal Eocene genus as noted 

 by Cope in his 'Tertiary Vertebrata,' the angle of the jaw is inflected and 

 the dental foramen is at the apex of a deep fossa for the external pterygoid 

 muscle like that occurring in the Diprotodonts. The posterior portion of the 

 zygomatic arch is deep and extends to the occiput, the malar running well 

 back to the glenoid region, features seen in both Cynodonts and primitive 

 Marsupials. 



Cope also referred to Pohjmastodon, certain skeletal remains, but 

 according to Dr. Matthew this association is probably incorrect. 



