1-21 



racter, which relates to the different development of the temporal 

 muscles, and the varieties of dentition in the different genera. In 

 the Wombat the coronal surface offers an almost flattened tract, 

 bounded by two slightly elevated temporal ridges, which are upwards 

 of an inch apart posteriorly, and slightly diverge as they extend for- 

 wards to the anterior part of the orbit. 



" The skull of the Opossum presents the greatest contrast to that 

 condition, for the sides of the cranium meet above at an acute angle, 

 and send upwards from the line of their union a remarkably ele- 

 vated sagittal crest, which, in mature skulls, is proportionally more 

 developed than in any of the placental Carnivora, not even exempt- 

 ing the strong-jawed Hyaena. 



"The Thylacine and Dasyures, especially the Ursine Dasyure, 

 exhibit the sagittal crest in asomev/hat less degree of development. 

 It is again smaller, but yet well marked in the Koala andPerameles. 

 The temporal ridges meet at the lambdoidal suture in the Phalangers 

 and Hypsiprymni, but the size of the muscles in these does not re- 

 quire the development of a bony crest. In the Kangaroo the tem- 

 poral ridges, which are very slightly raised, are separated by an inter- 

 space of the third of an inch. They are separated for a proportion- 

 ally greater extent in the Petaurists; and in the smooth and convex 

 upper surface of the skull of Pet. sciureus, Pet. pijcjmaus, and in Myr- 

 mecobius the impressions of the feeble temporal muscles almost 

 cease to be discernible. 



" The zygomatic arches arc, however, complete in these as in all 

 the other genera: they are usually, indeed, strongly developed ; but 

 their variations do not indicate the nature of the food so clearly, or 

 correspond with the differences of animal and vegetable diet in the 

 same degree, as in the placental Mammalia. No Marsupial animal, 

 for example, is devoid of incisors in the upper jaw, like the ordinary 

 Ruminants of the placental series ; and the more complete dental 

 apparatus with which the herbivorous Kangaroos, Potoroos, Phalan- 

 gers, &c. are provided, and which appears to be in relation to the 

 scantier pasturage, and the dry and rigid character of the herbage or 

 foliage on which they browse, requires a strong apparatus of bone 

 and muscle for the action of the jaws, and the exercise of the termi- 

 nal teeth. There are, however, sufficiently marked differences in 

 this jiart of the marsupial skull ; and the weakest zygomatic arches 

 are those of the Insectivorous Perameles and Acrobates, in which 

 structure we may discern a correspondence with the edentate Ant- 

 eaters of the placental series. Still the difference of development is 

 greatly in favour of the Marsupial Insectivora. 



" The Hypsiprymni are next in the order of development of the 

 zygomatic arches, which again are proportionally much stronger in 

 the true Kangaroos. The length of the zygomata in relation to the 

 entire skull is greatest in the Koala and Wombat. In the former 

 animal they are remarkable for their depth, longitudinal extent, and 

 straight and parallel course. In the latter they have a considerable 

 curve outwards, so as greatly to diminish the resemblance which 

 otherwise exists in the form of the skull between the Wombat and 



