26 DR. E. LONNBERG ON DIGESTIVE [Jan. 14, 



of the molars reminds one of the same in the Hares and Rabbits. 

 In his above-quoted work Tullberg has already drawn attention 

 to this parallelism. The explanation given by that author of 

 the development of persistent pulps in the molars holds good 

 for the Wombat as well. He believes that such teeth have 

 been develojDed chiefly in animals which feed on hard and tough 

 roots. Such animals must take much sand into the mouth when 

 feeding, and the sand must act strongly upon the crowns of the 

 molars in the act of grinding. This renders persistent growth 

 necessary. That the food of the Wombat consists mainly of 

 roots is a well-known fact ; and a glance at the crowns of the 

 molars suffices to show the marks of the sand as transverse 

 scratches. Although the molars of the Wombat in their general 

 shape resemble those of a Rabbit, the chewing mvist take place in 

 quite a different manner in both forms \ as can be seen fi'om a 

 comparison of the structure of the mandible in both animals. 



The dentition of the Phalangerids has been described by Flower 

 and Lydekker in their valuable manuaP. They have drawn 

 attention to the " crescentoid " cusps of the molars in Pseudo- 

 chirus and in the Koala '' recalling those of the Selenodont 

 Artiodactyle Ungulates." This " subselenodont " dentition is, of 

 course, very suitable for phyllophagous animals. It becomes the 

 more effective because the distance between the upper molar 

 series is greater than that between the mandibvilar molar series, 

 so that the outer row of cusps of the latter fit in between both 

 rows of the upper. Through this arrangement the jaws get as 

 it were a cutting-power, and when the lower jaw is moved side- 

 ways the sharp enamel ridges have a great power of tearing and 

 grinding the food. It is, in fact, evident that the chewing of the 

 food takes place in the following manner : — The lower jaw is 

 moved towards one side so much that the outer margin of its 

 molars corresponds to the outer margin of the upper molars. If, 

 then, both jaws are pressed hard against each other the lower 

 jaw must glide, with triturating effect, in a median direction— 

 in consequence of the fact that the main surface of the upper 

 molars slopes inward — till the outer cusps of the lower molars fit 

 in between both series of cusps of upper molars as described 

 above. Then the same movements are repeated again on the 

 same or the other side. The movements of the jaws in the act 

 of chewing may thus be compared with those in the Ruminants 

 — as might be expected seeing that the teeth have a similar 

 structure and position. 



The incisors in these two animals are different in shape. In 

 the Koala they are comparatively narrowei- than in Pseudochirus. 

 The compressed mandibular incisors glide with their bevelled 

 ends inside the upper median incisors, and work against the 

 second pair of upper incisors ; the latter in their styliform shape 



1 This is also I'Gmarkcd by Tullberg {I. c). 



" An Introduction to the Study of Mammals. London, 1891. 



