122 



the herbivorous Rodentia of the placentai series, as, e. g., the Fi*. 

 caccia. 



" In the carnivorous Marsupials the outward cun'e of the zygo- 

 matic arch (\vhich is greatest in the Thylacine and Ursine Dasyure,) 

 is also accompanied by a slight curve upwards ; but this curvatuie is 

 chiefly expressed by the concavity of the lower margin of the zygo- 

 ma, and is by no means so well marked as in the placentai Carnivora. 

 It is remarkable that this upward curvature is greater in the slender 

 zygomata of the Perameles than in the sti'onger zygomata of the Da- 

 synres and Opossums. In the Koala and Phalangers there is also a 

 slight tendency to the upward cun-ature ; in the Wombat the out- 

 wardly expanded arch is perfectly horizontai. In the Kangaroothe 

 lo-wer margin of the zygoma describes a slightly undulating cun'e, 

 the middle part of which is convex down^Yards. 



" In many of the Marsupials, as the Kangaroo, the Koala, the Pha- 

 langers, and the Opossums, the superior margin of the zygoma be- 

 gins immediately to rise above the posterior origin of the arch. In 

 the Wombat an external ridge of bone coramences at the middle of 

 the lo'vver margin of the zygoma, and gradually extends outwards 

 as it advances forwards, and, being joined by the upper margin of 

 the zygoma, forms the lower boundary of the orbit, and ultimately 

 curves downvvards in front of the ant-orbital foramen, below \vhich 

 it bifurcates, and is lošt. This ridge results, as it vrere, from the 

 flattening of the anterior part of the zygoma, which thus forms a 

 smooth and slightly concave horizontai platform for the eye to ręst 

 upon. The šame structure obtains, but in a slighter degree, in the 

 Koala. In the Kangaroo the anterior and inferior part of the zygoma 

 is extended downwards in the forra of a conical process, \vhich 

 reaches below the level of the grindlng teeth. A much shorter and 

 more obtuse process is observable in the corresponding situation in 

 the Phalangers and Opossum. 



" The relative length of the facial part of the skuU, anterior to 

 the zygomatic arches, varies remarkably in the different Marsupial 

 genera. In the Wombat it is as six to nineteen ; in the Koala as five 

 to fourteen ; in the Phalangers it forms about one-third of the length 

 of the entire skull ; in the carnivorous Dasyures and Opossums it is 

 more than one-third. In Perameles, Macropus, and Hypsiprymmis 

 murinus, 111., the length of the skull anterior to the orbit is equal 

 to the remaining posterior part ; but in a species of Hypsiprymnus 

 from Van Diemen's Land {Hypsiprymnus tnyosurus, Ogilb.) the 

 facial part of the skull anterior to the orbit exceeds that of the re- 

 mainder ; and the arboreal Hypsiprymni from New Guinea present a 

 still greater length of muzzle. In most Marsupials the skull gradually 

 converges towards the anterior extremity, but in the Perameles 

 lagotis the skull is remarkable for the sudden narrowing of the face 

 anterior to the orbits, and the prolongation of the attenuated snout, 

 preserving the šame diameter for upwards of an inch beforeit finally 

 tapers to the extremity of the nose. Inthe Koala the corresponding 

 part of the skull is as remarkable for its shortness as it is in the 

 Per. lagotis for its length, but it is bounded laterally by parallel lines 



