132 



finally, terminates by wide apertures behind tbe bony palate. In 

 the skull the nasal cavity communicates with the mouth, as before- 

 mentioned, by means of the various large vacuities in the palatal 

 processes. 



" The lower jaw of the marsupiata is a part of their osseous struc- 

 ture which claims more than ordinary attention, in consequence of 

 the discussions to which the fossil specimens of this bone, discovered 

 in the oolitic strata of Stonesfield, have given rise. I have examined 

 the two specimens in the possession of Dr. Buckland, the specimen 

 formerly in the collection of Mr. Broderip, and that which is pre- 

 served in the Museum at York ; the composition of the lower jaw, 

 each ramus of which consists of one j^iece of bone, the convex condyle, 

 and the double fangs of the molar teeth, prove the mammiferous 

 character of these remains ; the size, elevation, and form of the 

 coronoid process of the lower jaw, the production of the angle 

 of the jaw, with the development of the canines, and the pointed 

 tubercular crowns of the molar teeth, indicate the carnivorous 

 and insectivorous character of the species in question. The number 

 of the incisors, eight in the lower jaw, and the structure and propor- 

 tions of the molar teeth, approximate these small insectivora most 

 nearly to the smaller species of the modern genus Didelphis ; but 

 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 WTote 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 tlie lower jaw. — (See Mr. Waterhouse's 

 Memoir, Zuol. 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, tlie 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 sliglitly 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 wasseter acts upon 

 the jrfw. 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 an)' 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- 



