80 ARKIV FÖR ZOOLOGI. BAND 14. N:0 4. 



remainder of the crowns work against tlie crowns of tbe lower 

 molars with a crusliing and grinding effect. For the latter 

 process it is necessary that the jaw is movable, not only 

 vertically, but also in such a way that the surfaces of the 

 crowns of the upper and lower molars slide against each 

 other. If an experiment is made for trial, it is foiind, that 

 the teeth are worn in such a way, that the lower jaw can 

 most easily be moved forwards and backwards, meanwhile 

 the molars of both jaws are in contact and slide against 

 each other. 



To allow such movements the condyle of the lower jaw 

 must have another shape than in Didelphyidae and most 

 other Marsupials.^ Jn these animals the mandibular condyle 

 generally bas the shape of a transverse cylinder, more or 

 less as in the Carnivora. Such an articulation is of course 

 very steady, but it does not allow any movements of the 

 lower jaw except in the vertical plane. The mandibular 

 condyle of Caenolestes is quite different. It hasa flat, some- 

 what convex articular surface, which is nearly as long as 

 broad. Its transverse diameter is in an old C. fuscus 1,6 

 mm and the antero-posterior 1,8 mm. (In the female of the 

 same species much smaller, resp. 1 mm & 1,2 mm). In cor- 

 respondence to this the fossa glenoidea is flat and wide to 

 allow the movements. 



Stränge to say the mandibular condyle bas a strong 

 resemblance to the same of a Macropus, in spite of the fact 

 that this animal has no direct affinity with Caenolestes and 

 an entirely different diet. The likeness is, however, not con- 

 fined to the mandibular condyle of these animals. The man- 

 dibular incisors of Macropus fit in with their sharp lateral 

 cutting edges between the cutting edges of r' and i^ of the 

 upper jaw, so that a pair of scissors is formed by these teeth 

 just as in Caenolestes. Thus the former cuts grass by means 

 of the same arrangement and shape of the incisors as that, 

 which enables the latter to cut to pieces the insects, upon 

 which it preys. The further grinding of the grass resp. the 

 insects is afterwards effected by similar movements of the 

 lower jaw against the upper. 



The likeness between the mandibular apparatus of Cae- 

 nolestes and that of Macropodidae is increased by the fact 



^ Except Macropodidae and some others. 



