MARSUPIALIA. 



275 



of the falciform ligament as in the Ornitho- 

 rhynchus. 



The anterior depression or olfactory division 

 of the cavity of the cranium, as it may be 

 termed from its large size, is separated in a 

 well-marked manner from the proper cerebral 

 division of the cavity. It is relatively smallest 

 in the Koala. In all Marsupials it is bounded 

 anteriorly by the cribriform plate of the aeth- 

 moid bone, which is converted into an osseous 

 reticulation by the number and size of the 

 olfactory apertures. The cavity of the nose, 

 from its great size and the complication of 

 the turbinated bones, forms an important part 

 of the skull. It is divided by a complete 

 bony septum to within one-fourth of the an- 

 terior aperture ; the anterior margin of the 

 septum is slightly concave in the Koala; de- 

 scribes a slight convex line in the Wombat, 

 Kangaroo, and Phalanger, and a sigmoid 

 flexuie in the Dasyure. A longitudinal ridge 

 projects downwards from the inside of each of 

 the nasal bones, and is continued posteriorly 

 into the superior turbinated bone ; this bone 

 extends into the dilated space anterior to the 

 cranial cavity, which corresponds with the 

 frontal sinuses. The convolutions of the middle 

 spongy bone are extended chiefly in the axis of 

 the skull ; the processes of the anterior con- 

 voluted tone are arranged obliquely from 

 below upwards and forwards. They are ex- 

 tremely delicate and numerous in the Da- 

 syures and Phalangers ; they consist of thin 

 laminae of bone beautifully arranged on the 

 convex surface of the os turbinatum, and 

 placed vertically to that surface in the Po- 

 toroo ; but the bone becomes very simple in 

 the Kangaroo, Koala, and Wombat. The 

 nasal cavity communicates freely with large 

 maxillary sinuses, and finally terminates by 

 wide apertures behind the 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. 



Maxilla inferior. The lower jaw of the 

 Marsupials is a part of their osseous structure 

 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. 

 These specimens, which are well known to the 

 English reader by the figures of them published 

 in the Bridgewater Treatise of Dr. Auckland, 

 and in the Elements of Geology of Mr. Lyell, 

 were regarded by Cuvier as appertaining to 

 the Marsupial series of Mammalia, and to be 

 nearly allied to the genus Didelphis. 



This opinion of the great founder of Oryc- 

 tological Science has been called in question 

 by other naturalists, and has been more espe- 

 cially opposed by Professor De Blainville, who 

 conceives it to be more probable that they be- 

 long to a genus of Saurian Reptiles than to 

 the Didelphis or any genus of insectivorous 

 Mammals. I have examined the two speci- 

 mens in the possession of Dr. Buckland, the 

 specimen formerly in the collection of Mr. 

 Broderip and now in the British Museum, and 

 that which is preserved in the Museum at York. 



The composition of the lower jaw, each ramus 

 of which consists of one piece of bone, the 

 convex condyle, broad and high coronoid pro- 

 cess, and the structure and mode of implan- 

 tation of the molar teeth, sufficiently attest the 

 mammiferous character of these remains : the 

 size, elevation, and form of the coronoid pro- 

 cess of the lower jaw, the process continued 

 from the angle of the ramus, with the tubercular 

 crowns of the molar teeth, indicate the carni- 

 vorous and insectivorous character of the spe- 

 cies in question. In the presence of canines 

 and the number of the incisors and molars, 

 one of these small Insectivora {Plmscolotheriurn) 

 approaches most nearly to the smaller species 

 of the modern genus Didelphis; while in the 

 structure of the molar teeth, and in the form 

 of the coronoid process, it very closely re- 

 sembles the Thylacinus. The number of the 

 molars in the other genus (Thylacotherium) 

 exceeds that of any known ferine Insectivore, 

 placental or marsupial. We have seen, how- 

 ever, that the marsupial Mynnecobius possesses 

 nine molars on each side of both upper and 

 lower jaws. Besides the osteological charac- 

 ters above alluded to, there is a peculiarity in 

 the lower jaw of the Marsupial animals, which 

 was first indicated by Cuvier in the genus 

 Didelphys, but which is not restricted to that 

 genus. In the carnivorous Marsupials, as the 

 Thylacine, the lower maxillary bone resembles 

 in general form that of the corresponding spe- 

 cies in the placental series, as the Dog : a 

 similar transverse condyle is placed low down 

 near the angle of the jaw, on a level with the 

 series of molar teeth ; a broad and strong 

 coronoid process rises high above the condyle, 

 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 boun- 

 dary 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 Carnivora (the seals ex- 

 cepted), a process, representing the angle of 

 the jaw, extends directly backwards from the 

 middle of the above ridge, which process gives 

 precision and force 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 muscular depression 

 of the ascending ramus in all the Marsupials, 

 it does not in any of them send backwards, 

 or in any other direction, a process correspond- 

 ing to that just described in the. Dog and other 

 placental Carnivora. The angle of the jaw 

 itself, in the Marsupials, is as if it were bent 

 inwards in the form of a process encroaching 

 in various shapes, and various degrees of deve- 

 lopment in the different Marsupial genera upon 

 the interspace of the rami of the lower jaw. 

 In looking directly upon the lower margin of 

 the jaw, we see, therefore, in place of the mar- 

 gin of a vertical plate of bone, a more or less 

 flattened triangular surface extended between 

 the external ridge, and the internal process or 

 inflected angle. This characteristic structure is 



T 2 



