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



blance is the greater because they have a more horizontal dii'ection 

 than in the advilt, in which latter they are also stouter, com- 

 pressed, and only provided with an edge at the end. In 

 the young the lower incisors, on account of their shape, 

 work against the two median pail's of the upper incisors when 

 the jaws are shut. In the adult they woi"k only against the 

 inside of the median pair of vipper incisors when in a normal 

 situation close to each other. The halves of the lower jaw are, 

 however, movable, more so in the young than in the adult. This, 

 together with the side way movements of the lower jaw, explains 

 also why the second pair of upper incisors are worn. The faculty 

 of moving the mandibular halves so that the lower incisors may 

 be separated from each other in the act of biting is, of course, 

 very useful in many cases ^. Thus, for instance, the animal is 

 capable of securing a much larger piece of some soft fruit " in 

 one bite through this arrangement, and when occasionally preying 

 upon animals or birds this faculty is also of importance. The 

 mobility of the mandibular halves consequently serves here other 

 purposes than in the Kangaroos and Pseudochirus. 



The upper canines are well developed in young and adult. The 

 molars of the young Cuscus show four well-developed pyramidal 

 cusps with radiating ridges, so that, as has been shown by 

 0. Thomas, they resemble in some degree those of the Koala. 

 The enamel of these cusps is, however, less developed in the 

 Ouscus, so that they are in the adult animal soon worn down to 

 such an extent that the crown becomes almost even, and only 

 peripherally suri-ounded by enamel. The teeth are then not 

 much adapted for any grinding action. The situation and 

 different sloping of the posterior and anterior molars are similar 

 to those described in Trichosurus. The action of the jaws 

 must consequently be similar, although the enamel is rather less 

 developed. To crush the pulp of fruits and similar matter the 

 teeth are, however, sufficient. The hindmost premolar of both 

 jaws lying just in front of the molar series is somewhat more 

 strongly developed than in Trichosurus, pointed and reminding 

 one a little of a canine. Those of the upper and lower jaw do 

 not touch each other as in Trichosurus, but the mandibular 

 premolar goes inside and in front of that of the maxillary. This 

 development of the last premolar may have some connection with 

 the alleged occasionally predatory habits of the animal. 



In Petaurus the median lower incisors ai'e very long and 

 slender. The median pair of upper incisors are longei- than the 

 others. They may thus, together with the lowei- incisois, form a 

 pair of pincers. It is also probable that the mandibular incisors 

 themselves may, because both halves of the lower jaw are quite 

 movable, act as a suitable implement for pinching and scratching 



1 The mobility of the mandibular halves of the Rodents and its causes have been 

 extensively discussed by Tullberg in his work quoted above, p. 345 and following. 



2 Tullberg has stated that Squirrels feeding on mushrooms separate their 

 incisors {I, c). 



