1-25 



nivorous Dasyures ; out\vards and a little backward3 in the Pera- 

 meles and Phalanger ; outvvards, backvvards, and upwards in the 

 Kangaroos ; and directly outwards in the Petaurists and Wombat : 

 but the diiferences of direction are but very slightly marked. 



"The sąuamous element of the temporal bone generally reaches 

 half-way from the root of the zygoma to the sagittal ridge or su- 

 ture : it is most developed in the Wombat, in which its superior 

 margin describes a reniarkably straight line. The zygomatic pro- 

 cess of the temporal bone is in general compressed, and much ex- 

 tended in the vertical direction in the Opossum, Dasyure, Phalanger, 

 Koala, and Kangaroo. In theWombal it curves out\vards from the 

 side of the head in the form of a compressed and almost horizontai 

 plate ; it is then suddenly twisted into the vertical position, to be 

 received in the notch of the raalar portion of the arch. 



" The cavity, corresponding to the sphenoidal buUa ossea in other 

 Marsupials, is in this species excavated in the lo'vver part of the sąua- 

 mous element of the temporal bone at the inner side of the articular 

 surface for the lower ja\v. 



•' This articular surface, situated at the base of the zygomatic pro- 

 cess, presents in the Marsupial, as in the placentai Mammalia, va- 

 rious forms, each manifesting a physiological relation to the struc- 

 ture of the teeth, and adapted to the reąuired movements of the 

 ja\vs in the various genera. In the herbivorous Kangaroo the gle- 

 ncid ca-^nty forms a broad and slightly convex surface, as in the Ru- 

 minants, aftbrding freedom of rotation to the lo\ver jaw in every di- 

 rection. In the Phalangers and Potoroos the articular surface is 

 ąuite plane. In the Perameles it is slightly convex from side to 

 side, and concave from behind forwards. In the Wombat it is form- 

 ed by a convex narrow ridge considerably extended, and slightly 

 concave, in the transverse direction. This ridge is not bounded by 

 any descending process posteriorly, so that the jaw is left free for 

 the movements of protraction and retraction ; but this structure is 

 ■«ndely different from that -vvhich facOitates similar movements in 

 the Uodentia. In these there is a longitudinal groove on each side, 

 in which the condyle of the lovver javi^ plays backwards Eind forvvards, 

 but is impeded in its lateral movements ; these, on the contrary, are 

 freely allovved to the Wombat, and the obliąue disposition of the 

 lines of enamel upon the molar teeth correspond with the various 

 movements of wliich the lower jaw of the Wombat is thus suscep- 

 tible. In the Koala the glenoid cavity is a transversely oblong depres- 

 sion, with a slight convex rising at the bottom ; indicating rotatory 

 movements of the jaw. In the carnivorous Dasyures it forms a con- 

 cavity still more elongated transversel}% less deep than in the placentai 

 Carnivora, but adapted, as in them, to a ginglymoid motion of the 

 lower jaw ; the joint differs in the absence of an interarticular car- 

 tilage in the Marsupial Carnivora. In all the genera, save in the 

 Wombat, retraction of the lower jaw is opposed by a descending 

 process of the temporal bone immediately anterior to the meatus 

 auditorius and tympanic bone. 



"The glenoid cavity presents a characteristic structure in tbe 



