1 902.] ADAPTATIONS IN DIPROTODONT MARSUPIALS. 29 



small insects from their refuge in flowers, in cracks in the bark, 

 and similar places where these slender incisors may conveniently 

 be insei-ted. When securing larger insects this can, of course, 

 be more easily done with the incisors separated so that they act 

 as a fork, than if they lie close together and form only one point. 

 The molars have four moderately developed bluntly pointed 

 cusps. The lateral row of cusps of the mandibular molars fits in 

 between both rows of cusps of the upper molars. 



On the whole the dentition may be said to approach the 

 insectivorous type. The molars can certainly not be used for the 

 grinding of any hard vegetable matter, and the incisors are too 

 weak to gnaw. 



In Acrohates the development has gone still further in the 

 same direction. The median lower incisors are long and slender, 

 although, if compared with the skull itself, not so long as in 

 Petattrus, which has a shorter, less pointed snout. They may 

 certainly serve as pincers and the mandibular halves are quite 

 movable. The premolars of Acrohates are much better developed, 

 longer, and more pointed than those of Petaxmms. When the 

 jaws shut, the premolars of the upper and lower jaws meet, and 

 the latter slide up in front of the former. These teeth may thus 

 help in catching and holding the prey, which is not the case in 

 Petaurus. In the latter the premolars and second incisors of the 

 lower jaw ai'e small and functionless. This is because, in con- 

 sequence of the leng-th of the median incisors and the corresponding 

 shortness of the jaw itself, there is formed a considerable opening 

 between the upper and the lower jaw corresponding to the canine 

 and premolar region of the maxillary. The maxillary teeth thus 

 cannot meet the mandibular teeth, which do not even lie opposite 

 to them. The molars of Acrohates are similar to those of 

 Petaitrus, but tlieir cusps are sharper. It may be in conse- 

 quence of the arrangement of the premolars and their vise that 

 Acrohates has been able to reduce its number of molars to 3/3 

 when Petattrus has 4/4. 



In none of the Phalangerids which have the rami of the lower 

 jaw movable, as described above, have I been able to detect in 

 my material any trace of such a transverse muscle as that which 

 is found in the Kangaroos at the base of the mandibular incisors, 

 and which has the function of approximating the inner edges of 

 these teeth. In the Kangaroos it is said by Leche ^ that the 

 mandibular incisors are separated from each other by the com- 

 bined action of the muscidi hiventer, mylohyoideus, and genio- 

 hyoideus. In his great work on the Rodents already quoted, 

 TuUberg states that m. tnasseter serves to break or bend the lower 

 margin of the mandible outwards, and that in such a case the 

 incisors become pressed close to each other. On the other hand, 

 the m. transversus mandihuke, when contracting, approaches the 

 lower margins of the mandibular rami towards the median line, 



1 Bvonn : Kl. u. Ordn. d. Thierr., Saugethiere, vi. 5. 1. p. 681. 



