336 ANATOMY OF VERTEBRATES. 



union a remarkably elevated sagittal crest, which, in mature 

 skulls, is jDroportionally more developed than in any of the pla- 

 cental Carnivora, not even excepting the strong-jawed Hyjena. 

 The Thylacine and Dasyures, especially the Ursine Dasyure, ex- 

 hibit the sagittal crest in a somewhat less degree of developement. 

 It is again smaller, but yet well marked, in the Koala and Pera- 

 meles. The temporal ridges meet at the lambdoidal suture in the 

 larger Phalangistce and in the Hypsiprymni, but the size of the 

 muscle in these does not require the developement of a bony crest. 

 In the Kangaroo, the temporal ridges, which are very slightly 

 raised, are separated by an interspace of the third of an inch. 

 They are separated for a proportionally greater extent in the 

 Petaurists, especially Petaurus flaviventer ; and in the smooth 

 and convex upper surface of the skull of Petaurus sciureus, Pet 

 pigmceus, Myrmecobius, the impressions of the feeble temporal 

 muscles almost cease to be discernible. 



The zygomatic arches are, 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. And 

 this is not surprising when we recollect that no Marsupial ani- 

 mal is devoid of incisors in the upper jaw, like the ordinary 

 Ruminants of the placental series : accordingly the more com- 

 plete dental system with which the herbivorous Kangaroos, 

 Potoroos, Phalangers, &c., are provided, and which appears to be 

 in relation to the scantier pasturage and the dry and rigid cha- 

 racter of the herbage or foliage on which they browse, requires a 

 stronger apparatus of bone and muscle for the action of the jaws, 

 and especially for the working of the terminal teeth. There are, 

 however, well-marked differences in this part of the Marsupial 

 skull ; and the weakest zygomatic arches are those of the Insecti- 

 vorous Perameles and Acrobates, in which structure we may 

 discern a correspondence with the Edentate Anteaters of the 

 placental series. Still the difference in the developement of the 

 zygomata is greatly in favour of the Marsupial Insectivora. 



The Hypsiprymni come next in the order of developement 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 and 

 straight and parallel course, as well as for their longitudinal ex- 

 tent, fig. 221. In the Wombat, fig. 220, they have a considerable 



