MARSUPIALIA. 263 



The orbit is enormous, aud there is a large antorbital foramen/ The 

 great upper sectorial tooth is evidently the last premolar, and is fixed by 

 two roots, while its extremely compressed crown is marked by a few fine 

 vertical flutiugs or grooves. The four molars immediately behind this 

 tooth have quadricuspidate crowns, less elevated, and often with a small 

 accessory cusp at the antero-external angle. The lower dentition (fig. 154) 

 is especially remarkable because the sectorial tooth, shaped like that of 

 the upper jaw opposing it, seems to be the first molar. In front there is 

 the pair of relatively enormous incisors ; then follow five very small simple 

 teeth with a single root, which have been interpreted as one canine and 

 four premolars ; next comes the sectorial ; and finally there are three 

 cuspidate molars, the two first like those of the upper jaw, the last smaller 

 and more elliptical in shape. 



The diminutive South American Diprotodonts, so far as 

 known, exhibit free and unmodified digits in each foot. All the 

 Australian forms, on the other hand, are " syndactylous," having 

 two or more digits, at least in the hind feet, enclosed in a 

 common integument; and this strange specialization culminates 

 in the leaping hind foot of the kangaroos. 



Among these Australian groups, the existing family of 

 Phalangeridae, or phalangers, are probably the most closely 

 related to the South American Epanorthidue ; but practically 

 nothing is known of their ancestry, and the only extinct genus 

 of special interest generally believed to be allied to them, is 

 Thylacoleo. This is the " pouched lion " of Owen, represented 

 by remains of the skull, and probably by certain limb-bones, 

 in the superficial deposits of Queensland, Victoria, and New 

 South Wales. The animal is believed to have been carnivorous 

 by those who base their conclusions on the reduced tubercular 

 character of the true molars and the low position of the condyle 

 of the mandible ; it is considered to have been a herbivore or 

 a mixed feeder by those who emphasize the fact that no known 

 existing carnivore has canines too small for grasping. 



Thylacoleo (fig. loo). The skull is short and broad, with relatively 

 large temporal fossae, and a robust zygomatic arch, but the orbit not com- 

 pletely enclosed behind. There is one pair of large palatine vacuities. 



The dental formula is .',* ' ' ^ ' ' . The anterior pair of upper 



i. 1, c. 0, pm. 3, in. 2 



incisors is much enlarged, while the two following incisors, the canine, and 

 first two premolars are merely small obtuse cones, crowded together, and 



