_Abderites_ is also typically Diprotodont by reason of the large projecting incisors of the lower jaw. It has a large cutting tooth in the lower jaw, which appears to be the last premolar, and is thus comparable to the great cutting tooth of the lower jaw and of the upper jaw of the extinct Phalanger, _Thylacoleo_. {149} It may also be comparable to the great premolar of such Multituberculata as _Ptilodus_ and _Plagiaulax_. It is, moreover, marked with vertical grooves. An interesting form, which is unfortunately but little known, is the Australian and Pleistocene genus _Triclis_, with one species, _T. oscillans_. In having a minute canine tooth in the lower jaw it agrees with some Phalangeridae, and being otherwise closely allied to _Hypsiprymnodon_, it unites the Macropodidae with the Phalangeridae. SUB-ORDER 2. POLYPROTODONTIA. In this mainly carnivorous or insectivorous division of the Marsupials the incisors are four or five on each side of the upper jaw, and one or two fewer in the lower jaw. Figs. 76 and 77 illustrate the Polyprotodont and Diprotodont dentitions. The canines are those of flesh-eaters and so are the molars, being as a rule sharply cuspidate. As a rule, which has an exception in the Peramelidae, there is no syndactylism of toes in the hind-foot. This sub-order is at the present day Australian and American in its range. [Illustration] FIG. 76.--Front view of the skull of Tasmanian Devil (_Sarcophilus ursinus_), showing Polyprotodont and carnivorous dentition. (After Flower.) FAM. 1. DASYURIDAE.--This family consists of Marsupials which are generally pentadactylous, but with occasionally the hallux missing. The tail is long but not prehensile. The pouch is present or absent. The teeth vary in the different genera, but {150} the upper incisors are never less than three, and may be as many as five in the upper jaw and six in the lower. The canines are trenchant. There is no caecum. [Illustration] FIG. 77.--Front view of skull of Koala (_Phascolarctos cinereus_), illustrating Diprotodont and herbivorous dentition. (From Flower.) [Illustration] FIG. 78.--Longitudinal section of the skull of the Thylacine (_Thylacinus cynocephalus_). x 1/2. _a_, Angular process of mandible; _AS_, alisphenoid; _BO_, basioccipital; _BS_, basisphenoid; _cd_, condyle of mandible; _ET_, ethmoturbinal; _Ex.O_, exoccipital; _Fr_, frontal; _ME_, ossified portion of mesethmoid; _MT_, maxilloturbinal; _Mx_, maxilla; _Na_, nasal; _OS_, orbitosphenoid; _Pa_, parietal; _Per_, periotic; _Pl_, palatine; _PMx_, premaxilla; _PS_, presphenoid; _Pt_, pterygoid; _SO_, supraoccipital; _Sq_, squamosal; _Vo_, vomer. (From Flower's _Osteology_.)