450 Zoological Society, 



the number of the molars in one of the specimens exceeds that of 

 any insectivore, placental, or marsupial, which was known at the 

 period when Cuvier wrote on this fossil. Recently, however, 

 a genus of insectivorous mammal (Myrmecobius) has been dis- 

 covered in Australia, presenting the modifications of the cranium 

 which characterize the marsupiata, and having nine tuberculate 

 molares in each ramus of the lower jaw. — (See Mr, Waterhouse' s 

 Memoir, Zool. Trans, ii. pi. 28. fig. 2, 5.) Besides the osteolo- 

 gical characters above alluded to, there is a character in the lower 

 jaw of the marsupial animals, not peculiar to the genus Didelphis, 

 which serves to distinguish it from that of the placental mammalia. 

 In the carnivorous marsupials, as the Thylacine, the lower maxillary 

 bone very nearly resembles in general form that of the corresponding 

 placental species, as the dog ; a similar transverse condyle is placed 

 low down, near the angle of the jaw; the strong coronoid process rises 

 high above it, and is slightly curved backwards ; there is the same well- 

 marked depression on the exterior of the ascending ramus for the firm 

 implantation of the temporal muscle, and the lower boundary of this 

 depression is formed by a strong ridge extended downwards and 

 forwards from the outside of the condyle. But in the dog and 

 other placental digitigrade Carnivora, a process, representing the 

 angle of the jaw, extends directly backwards from the middle of 

 the above ridge, which process gives fixation to the articulation of 

 the jaw, and increases the power by which the masseter acts upon 

 the jaw. Now, although the same curved ridge of bone bounds 

 the lower part of the external depression of the ascending ramus in 

 all the marsupiata, it does not in any of them send backwards, or 

 in any other direction, a process corresponding to that just de- 

 scribed in the dog. The angle of the jaw is as if it were bent in- 

 wards in the form of a process encroaching in various shapes and va- 

 rious degrees of development, in the different marsupial genera, upon 

 the interspace of the rami of the lower jaw. In looking down upon 

 the lower margin of the jaw, we see therefore, in place of the margin 

 of a vertical plate of bone, a more or less flattened surface extended 

 between the external ridge and the internal process or inflected 

 angle. 



" The marsupial bones are elongated, flattened, and more or less 

 curved, expanded at the proximal extremity, which sometimes, as in 

 the Wombat, is articulated to the pubis by two points ; they are rela- 

 tively longest, straightest, and most slender in the Perameles ; flattest, 

 broadest, and most curved in the Koala. They are always so long 

 that the creraaster muscle winds round them in its passage to the 



