262 



MARSUPIALIA. 



into a thumb, but without a claw. The hinder 

 hand is associated in almost all the species 

 with a scaly prehensile tail. 



In some of the smaller Opossums the sub- 

 abdominal tegumentary folds are rudimental, 

 or merely serve to conceal the nipples, and are 

 not developed into a pouch : the young in 

 these species adhere to the mother by entwining 

 their little prehensile tails around her's ; and 

 they cling to the fur of the back, hence the 

 term dorigera applied to one of these Opos- 

 sums.* 



Tribe III. CARPOPHAGA. 



Stomach simple ; coecum very long. 



In this family the teeth, especially those at 

 the anterior part of the mouth, present consider- 

 able deviations from the previously described 

 formulae ; the chief of which is a predomi- 

 nating size of the two anterior incisors, both 

 in the upper and lower jaws. Hitherto we 

 have seen that the dentition in every marsupial 

 genus has participated more or less in a carni- 

 vorous character ; henceforth it will manifest a 

 tendency to the Rodent type. 



Genus PHALANGISTA. 



The Phalangers, so called from the phalanges 

 of the second and third digits of the hinder ex- 

 tremity being inclosed in a common sheath of 

 integument, have the innermost digit modi- 

 fied to answer the purposes of a thumb ; and 

 this hinder hand being associated in many of 

 the species with a prehensile tail, they evidently, 

 of all Frugivora, come nearest to the arboreal 

 species of the preceding section. In a system 

 framed on locomotive characters they would 

 rank in the same section with the Opossums. 

 We shall see, however, that they differ from 

 those Entomophagous Marsupials in the con- 

 dition of the intestinal tube. Let us examine 

 to what extent the dental characters deviate 

 from those of the Opossums. 



Fig. 86. 



Phalaiirjista Cookii. 



In the skull of a Phalangixta Cookii, of 

 which the dental formula is accurately given 

 in Jig. 86, there are both in the upper and 

 lower jaws four true molars on each side, each 



* Few facts would be more interesting in the 

 present branch of zoology than the condition of 

 the new-born young, and their degree and mode of 

 uterine development in these Opossums. Since 

 the marsupial bones serve, not as is usually de- 

 scribed to support a pouch, but to aid in the func- 

 tion of the mammary glands and testes, they of 

 course are present in the skeleton of these small 

 pouchless Opossums as iu the more typical Mar- 

 suitiis* 



beset with four three-sided pyramidal sharp- 

 pointed cusps ; thus these essential and most 

 constant teeth correspond in number with those 

 of the Opossum : but in the upper jaw they 

 differ in the absence of the internal cusp, which 

 gives a triangular figure to the grinding surface 

 of the molars in the Opossum ; and the an- 

 terior single cusp is wanting in the true molars 

 of the lower jaw. Anterior to the upper 

 grinders in this Phalanger there are two pre- 

 molars of similar shape and proportions to 

 those in the Opossum ; then a third premolar, 

 too small to be of much functional importance, 

 separated also, like the corresponding anterior 

 premolar in the Opossum, by a short interval 

 from those behind. 



The canine tooth but slightly exceeds in size 

 the above false molar, and consequently here 

 occurs the first great difference between the 

 Phalangers and Opossums ; it is, however, 

 but a difference in degree of development ; and 

 in the Ursine and other Phalangers, as well as 

 in the Petaurists, the corresponding tooth pre- 

 sents more of the proportions and form of a 

 true canine. 



The incisors, which we have seen to be most 

 variable in number in the Carnivorous section, 

 are here three instead of five on each side of 

 the upper jaw, but their size, especially that of 

 the first, compensates for their fewness. 



In the lower jaw there is the same number 

 of molars and functional premolars as in the 

 Opossums; the two very minute and function- 

 less molars, which form part of the same con- 

 tinuous series, represent the small premolar and 

 canine of the upper jaw; and anterior to these 

 there is one very small and one very large and 

 procumbent incisor on each side. Now if this 

 comparison be just and natural, the difference 

 in the number of teeth between the Phalanger 

 and the Opossum will resolve itself into the 

 former being minus certain incisors in the up- 

 per and lower jaws : in the latter, the great 

 development of the middle incisors seems to 

 produce an atrophy of all the rest. 



The interspace between the functionally de- 

 veloped incisors and molars in both jaws always 

 contains in the Phalangers teeth of small size 

 and little functional importance, and variable 

 not only in their proportions but their number. 



The constant teeth in the Phalangers are the 



true molars, and the __ _ incisors. 



44 



11 



Fig. 87. 



