268 



MAKSUPIALIA. 



of notice. The Kuala, like the Phalangers and 

 Kangaroos, has 13 pairs of ribs ; but this class 

 of characters will form the subject of the fol- 

 lowing section. 



OSTEOLOGY OF THE MARSUPIALIA. 



Of the Skull. The form of the skull 

 varies much in different Marsupial animals, 

 but it may be said, in general terms, to re- 

 semble an elongated cone, being terminated by 

 a vertical plane surface behind, and in most 

 of the species converging towards a point ante- 

 riorly : it is also generally more depressed or 

 flattened than in the placental Mammalia. The 

 skull is also remarkable in all the Marsupial 

 genera for the small proportion which is de- 

 voted to the protection of the brain, and for the 

 great expansion of the nasal cavity immediately 

 anterior to the cranial cavity. 



In the stronger carnivorous Marsupials the 

 exterior of the cranium is characterized by bony 

 ridges and muscular impressions, but in the 

 smaller herbivorous and insectivorous species, 

 as the Petaurists, Potoroos, and Myrmecobius, 

 the cranium presents a smooth convex surface 

 as in Birds, corresponding with the smooth un- 

 convoluted surface of the simple brain con- 

 tained within. 



The breadth of the skull in relation to its 

 length is greatest in the Wombat,* Ursine Da- 

 syuref and Petaurists, in which it equals three- 

 fourths of the length, and is least in the Peru- 

 tnelcs lagotis, in which it is less than one-half. 



The occipital region, which is generally plane, 

 and vertical in position, forms a right angle 

 with the upper surface of the skull, from which 

 it is separated by an occipital or lambdoidal 

 crista. This crista is least developed in the 

 Myrmecobius, Petaurists, and Kangaroos, and 

 most so in the Thylacine and larger Opossums, 

 in which, as also in the Koala, the crest curves 

 slightly backwards, and thus changes the occipi- 

 tal plane into a concavity for the firm implanta- 

 tion of the strong muscles from the neck and back. 



The upper surface of the skull presents great 

 diversity of character, which relates to the dif- 

 ferent 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 forwards to the anterior part of 

 the orbit. 



The skull of the Virginian Opossum pre- 

 sents 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 elevated sagittal crest, which, 

 in mature skulls, is proportionally more deve- 

 loped than in any of the placental Carnivora, 

 not even excepting the strong-jawed Hyaena. 



The Thylacine and Dasyures, especially the 

 Ursine Dasyure, exhibit the sagittal crest in a 

 somewhat less degree of development. It is 

 again smaller, but yet well marked in the Koala 

 and Perameles. The temporal ridges meet at 



As 15 to 20. t As 10 to 14. 



the lambdoidal suture in the larger Phnlangisttc 

 and in the Hypsiprymni, but the size of the 

 muscles in these does not require the deve- 

 lopment 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. pignueus, Myrmecobius, the im- 

 pressions 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 diffe- 

 rences 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 animal 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 pro- 

 vided, 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 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 diffe- 

 rences in this part of the Marsupial skull ; and 

 the weakest zygomatic arches are those of the 

 Insectivorous Perumeles and Acrobates, in 

 which structure we may discern a correspon- 

 dence with the Edentate Anteaters of the pla- 

 cental series. Still the difference in the deve- 

 lopment of the zygomata is greatly in favour of 

 the Marsupial Insectivora. 



The Hypsiprymni come 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 and straight 

 and parallel course, as well as for their longi- 

 tudinal extent. In the Wombat they have a 

 considerable curve outwards, so as greatly to 

 diminish the resemblance which otherwise ex- 

 ists in the form of the skull between this Mar- 

 supial and the Herbivorous Kodentia of the 

 placental series, as, e. g. the Viscaccia. 



In the carnivorous Marsupials the outward 

 sweep of the zygomatic arch, which is greatest 

 in the Thylacine und Ursine Dasyure, is also 

 accompanied by a slight curve upwards, but 

 this curvature is chiefly expressed by the con- 

 cavity of the lower margin of the zygoma, and 

 is by no means so well marked as in the 

 placental Carnivora. It is remarkable that this 

 upward curvature is greater in the slender 

 zygomata of the Perameles than in the stronger 

 zygomata of the Dasyures and Opossums. In 

 the Koala and Phalangers there is also a slight 

 tendency to the upward curvature; in the 



