298 



MARSUPIALIA. 



angle of the jaw. The preceding description is 

 taken from a dissection of the Koala. The 

 masticatory muscles of the Wombat differ only 

 in their relative proportions ; the masseter in 

 this gliriform Marsupial is single, presenting no 

 trace of that subdivision and modified attach- 

 ments which adapt it to the protraction of the 

 lower jaw in the true Rodents, and accordingly 

 the structure of the joint of the lower jaw of 

 the Wombat exhibits, as already described, a 

 corresponding difference from the Rodent 



type- 

 There is no toothless genus among the true 



Marsupials, unless the Monotremes which re- 

 present the Edentate order of the Placental 

 Mammalia be regarded as modified Marsupials. 

 Molar and incisor teeth are present in botli 

 jaws in every true Marsupial species ; the ca- 

 nines are but feebly represented in many, as the 

 Phalangers, Petaurists, &c. are wanting in the 

 lower jaw in the Potoroos and Koala, and in 

 both jaws in the Kangaroos and 'Wombat. The 

 grinders, on the other hand, present their most 

 complicated structure in these last cited herbi- 

 vorous genera. 



The Dasyures and Thylacine offer the carni- 

 vorous type of the dental system, but differ 

 from the corresponding group of the Placental 

 Mammalia in having the molars of a more 

 uniform and simple structure, and the incisors 

 in greater number ; which number, however, is 

 different in the different Marsupial carnivorous 

 genera, as is expressed in the dental formulae 

 already given. 



The canines are as formidable for their size, 

 shape, and strength in the Thylacine and Ur- 

 sine Dasyure, as in the Dog or Cat, and in a 

 fossil species of the latter genus (Dasyurus 

 Inniarius)* which co-existed, in ancient Aus- 

 tralia, with herbivorous Marsupials of greater 

 size than now inhabit that continent, these 

 teeth were as large as in the Leopard. In 

 the Thylacine the points of the lower ca- 

 nines are received in hollows of the intermaxil- 

 lary palatal plate when the mouth is closed, 

 and do not project, as in the carnivorous pla- 

 centals, beyond the margins of the intermaxil- 

 laries. 



In some of the smaller species of the carni- 

 vorous group, as the P/iascogales, the canines 

 lose their great relative size, and the molar 

 teeth present a surface more cuspidated than 

 scctorial : there is also an increased number of 

 teeth, and as a consequence of their more equa- 

 ble development they have fewer and shorter 

 interspaces. Thus the Phascogale penicillata 

 has, as Mr. Hunter observed, " a mouth full of 

 teeth," and these are adapted for the capture 

 and mastication of insects and other small and 

 low organized animals. 



In the Opossums the canines still exhibit a 

 superior development in both jaws adapted for 

 the destruction of living prey, but the molars 

 have a conformation different from that which 

 characterises the true flesh-feeders, and they 

 consequently subsist on a mixed diet or lower 

 organized animals; some, as the web-footed 

 Cheironectes, betake themselves to the water, 



* Sec M.ii. i Mill-In li's .Australia, vol. ii. 



and prey, like the otter, on rish ; others prowj 

 about the sea-shore and subsist on Crustacea, 

 as the Didelphys cancrivora. 



The Perameles are for the most part insecti- 

 vorous ; the incisors are always very small, the 

 molars generally multicuspidate ; some species, 

 as Per. nasuta, have the canines not more de- 

 veloped than the premolars, which they closely 

 resemble ; but in others, as the Per. lagotis, 

 they are proportionally as large as in the 

 Opossums, and the inferior ones are concealed 

 in the same position when the mouth is closed, 

 as in the Thylacine. But the Per. lagotis, in- 

 stead of exhibiting a corresponding approach 

 in the structure of the molars to a carnivorous 

 diet, have these unerring indicators of the na- 

 ture of the food terminated by a broad oblique 

 flattened surface, adapted to the trituration of 

 farinaceous vegetable roots, the destruction of 

 which is confidently attributed to this species 

 of Bandicoot by the colonists of Swan River. 

 The interesting genus Myrmecobius offers, 

 in the small size and scattered distribu- 

 tion of its teeth, the nearest approach among 

 the Marsupials to the edentate group of the 

 Placental Mammalia ; the multicuspidate struc- 

 ture of the molar teeth, and their small size, 

 indicates that the Myrmecobius feeds chiefly 

 on the weaker insects which are implied by 

 its generic name. It is important to notice 

 that in many of the Marsupials there is an 

 inconstancy in the number of teeth in species 

 of the same genus, and sometimes even in 

 individuals in the same species; this at least 

 appears to be the case in the Myrmecobius, in 

 which, of three specimens examined, identical 

 in all other respects, one had forty-eight, the 

 other fifty-two, and the third fifty teeth. We 

 have already pointed out the variety which ob- 

 tains in the spurious and true molars of the 

 Phalangers and Petaurists. The prominent 

 feature in the change from the carnivorous to 

 the herbivorous type of dentition is the inordi- 

 nate development of the two middle incisors of 

 the lower jaw, atlhe expense, as it would seem, 

 of the posterior ones. In the Phalangista Cookii, 

 e. g. six incisors are always present in the lower 

 jaw, but only the first two have any functional 

 character : the canine tooth again offers neither 

 a form nor size by which it can be distinguished 

 from the spurious molars ; in the other Mar- 

 supials with the same characteristic modifica- 

 tion of the hinder feet, including the Petaurists 

 with the Phalangers, the small posterior incisors 

 are wanting wholly or in part ; the canines seem 

 also to be lost, and the spurious molars are 

 fewer, but variable in number. This incon- 

 stancy is not to be wondered at in teeth which 

 have too simple a form and too insignificant a 

 size to exercise any influence on the habits and 

 economy of the species ; and it would seem to 

 be lost labour in the zoologist to attempt to 

 found generic distinctions, and invent new 

 names for the species in which these insignifi- 

 cant varieties are presented. The six incisors 

 of the upper jaw and the two anterior ones in 

 the lower jaw, with the true molars in both 

 jaws, present a constancy of character and a 

 functional importance in their development in 

 all the Phalangers and Petaurists. These teeth 



