TEETH OF DIPHYODONTS. 



285 



lines above the sockets. The molars consist of a body of dentine, 

 a coronal covering of enamel, and a general investment of cement, 

 very thin upon the crown, and a little thicker upon the fangs. 



B. Marsupialia. In the Marsupial order, the typical number 

 of the teeth in the molar series is seven on each side of both jaws, 

 the first three of which are ( premolars/ fig. 221, p, i, 2, 3, the last 

 displacing, in some, a calcified predecessor, fig. 296, d 3, and giving 

 the extent of the theoretical deciduous series. Incisors, fig. 221, 

 i, are present in all the species, but are variable in number, in 

 some genera exceeding that of the Mammalian type. Canines, ib. 

 c, are large in the Dasyures, are feebly represented in the Phalan- 

 gers and Petaurists, are absent in the lower jaw of the Potoroos 

 and Koala (fig. 221, vol. ii), and in both jaws of the Kangaroos, 

 fig. 231, and Wombats, fig. 232. 



The Dasyures and Thylacine offer the carnivorous type of the 

 dental system, but differ from the corresponding group of the 

 placenta! Mammals in having the molars of a more uniform and 



221 



Dentition of Thylacine. 



simple structure, and the incisors in greater number : the dental 

 formula of the Dog-headed Opossum, Thylacinus, is- 



.4.4 1.1 3.3 4.4 



1 3~3' C lTI ' P 3~3' m 4~l = 46 ' g ' 22L 



The canine teeth are long, strong, curved, and pointed ; the 

 points of the lower canines are received in hollows of the pre- 

 maxillary palatal plate when the mouth is closed, and do not 

 project, as in the carnivorous placentals, beyond the margins of 

 the maxillary bones. The premolars, p, present a simple com- 

 pressed conical crown, with a posterior tubercle, which is most 

 developed on the hindmost. The molars, m, in the upper jaw are 

 unequally triangular, the last being much smaller than the rest ; 



