SKELETON OF MAKSUPIALIA. 337 



curve outward, so as greatly to dimmish the resemblance which 

 otherwise exists in the form of the skull between this Marsupial 

 and the Herbivorous Kodentia of the placental series, as, e. g., 

 the Viscaccia. 



In the carnivorous Marsupials the outward sweep of the zygo- 

 matic arch, Avhich is greatest in the Thylacine and Ursine 

 Dasyure, is also accompanied by a slight curve upward, but this 

 curvature is chiefly expressed by the concavity 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 cur- 

 vature is greater in the slender zygomata of the Perameles than 

 in the stronger zygomata of the Dasyures and Opossiuns. In 

 the Koala and Phalangers there is also a slight tendency to the 

 upward curvature ; in the Wombat the outwardly expanded arch 

 is horizontal. In the Kangaroo the lower margin of the zygoma 

 describes a slightly undulating curve, the middle part of which is 

 convex downward. 



In many of the Marsupials, as the Kangaroo, the Koala, some 

 of the Phalangers, Petaurists, and Opossums, the superior margin 

 of the zygoma begins immediately to rise above the posterior 

 origin of the arch. In the Wombat an external ridge of bone 

 commences at the middle of the lower margin of the zygoma, and 

 gradually extends outward as it advances forward, and being 

 joined by the upper margin of the zygoma, forms the lower 

 boundary of the orbit, and ultimately curves downward in front 

 of the antorbital foramen, below which it bifurcates and is lost. 

 This ridge results, as it were, from the flattening of the anterior 

 part of the zygoma, which thus forms a smooth and slightly con- 

 cave horizontal platform for the eye to rest upon. 



The same structure obtains, but in a" slighter degree, in the 

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

 zygoma is extended downward in the form of a conical process, 

 Avhich reaches below the level of the grinding-teeth ; it is de- 

 veloped from the maxillary. A much shorter and more obtuse 

 process is observable in the corresponding situation in the Pha- 

 langers and Opossums. 



The relative length of the facial part of the skull 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 Petaurus sciureus and Petaurus Bennettii 

 it forms about one-fourth of the entire skull ; in the Phalangers 

 about one-third ; in the carnivorous Dasyures and Opossums more 

 than one-third; in the Thylacine nearly one-half; in Perameles^ 



VOL. II. z 



