276 



MARSUPIALIA. 



clearly exemplified in the fossil jaw from the 

 Stonesfield oolite, in the British Museum, re- 

 presenting the extinct Marsupial which I have 

 termed Phascolotherium Bucklantiii. In the 

 Opossums the internal angular process is tri- 

 angular and triedral, directed inwards, with 

 the point slightly curved upwards, and more 

 produced in the small than in the large species. 

 In the Dasyures it has a similar form, but the 

 apex is extended into an obtuse process. In 

 the Thylacine the base of the inverted angle is 

 proportionally more extended, and a similar 

 structure is presented by the fossil Phascolo- 

 there. In the Perameles the angle of the jaw 

 forms a still longer process ; it is of a flat- 

 tened form extended obliquely inwards and 

 backwards and slightly curved upwards. It 

 presents a triangular, slightly incurved, and 

 pointed form in the Petaurists, in which it is 

 longest and weakest in the pigmy species, 

 (Acrobates, Desm.) It is shorter and stronger 

 in the Myrmecobius (fig- 97). In the Po- 

 toroos and Phalangers the process 

 Fig. 97. is broad with the apex slightly de- 

 veloped ; it is bent inwards and 

 bounds the lower part of a wide 

 and deep depression in the inside 

 of the ascending ramus. In the 

 great Kangaroo the internal margin 

 of this process is curved upwards, 

 so as to augment the depth of the 

 internal depression above men- 

 tioned. The internal angular pro- 

 cess arrives at its maximum of 

 development in the Wombat, 

 (fig. 94,) and the breadth of the 

 base of the ascending ramus very 

 nearly equals the height of the 

 same part. This broad base also 

 inclines downwards and outwards 

 from the inflected angle, and the 

 same peculiarity occurs in the 



Lower jaw, 



of the Phascolothere. In 



.. law \ji tut A 

 jilyrmecobnis. J , _, . , . _ , 



the Koala the size of the process 



in question is also considerable, but it 

 is compressed, and directed backwards with 

 the obtuse apex only bending inwards, so 

 that the characteristic flattening of the base 

 of the ascending ramus is least marked in 

 this species. There is no depression on the 

 inner side of the ramus of the jaw in the Koala, 

 but its smooth surface is simply pierced near 

 its middle by the dental artery. The surface 

 of the external muscular depression bounded 

 below by a broad angular ridge, as above de- 

 scribed, is entire in the Dasyures, Opossums, 

 Bandicoots, Petaurists, and Phalangers; but 

 in the Wombat the outer surface of the as- 

 cending ramus is directly perforated by a round 

 aperture immediately posterior to the com- 

 mencement of the dental canal :'* the corres- 

 ponding aperture is of larger size in the Kan- 

 garoo. But in the Potoroos both the external 

 and internal depressions of the ascending ramus 

 lead to wide canals, or continuations of the 

 wide depressions which pass forwards into the 



" A bristle is represented passing through this 

 aperture in fig. 94. 



substance of the horizontal ramus, and soofi 

 uniting into one passage, leave a vacant space 

 in the intervening bony septum. This struc- 

 ture, if it had been observed only in the jaw of 

 a fossil Marsupial, would have supported an 

 argument for its Saurian nature, more cogent 

 than any that have been adduced in the dis- 

 cussion of the Stonesfield fossils, on account of 

 the analogous vacuity in the jaw of the Cro- 

 codile. 



The commencement of the dental canal in 

 the Potoroos and Wombat is parallel with the 

 beginning of the molar series, and it has the 

 same relative position in the Stonesfield Mar- 

 supials ; but in the other carnivorous and in- 

 sectivorous species the dental foramen is placed 

 further back. In the Wombat a vascular groove 

 is continued from the foramen along the inner 

 side of the ramus of the jaw as in the Stones- 

 field fossils ; and a corresponding but wider 

 groove is present in the lower jaw of the Myr- 

 mecobius. In the Thylacine and Ursine Da- 

 syures and their fossil congener the Phascolo- 

 there, the condyle of the lower jaw is placed 

 low down, on a level with the molar series : 

 it is raised a little above that level in the smal- 

 ler Dasyures and Opossums, and ascends in 

 proportion to the vegetable diet of the spe- 

 cies. 



In all those Marsupials which have few or 

 very small incisors the horizontal rami of the 

 jaw converge towards a point at the symphysis. 

 The angle of convergence is most open in the 

 Wombat, and the gradual diminution in the 

 size of the rami as they approach this part is 

 most marked and direct. The internal surface 

 of the symphysis menti is almost horizontal, 

 and is convex from side to side in the interval 

 between the molars and incisors. The suture 

 becomes obliterated in aged individuals. It 

 is also wholly obliterated in the skull of a 

 Koala now before me ; in all the other Marsu- 

 pial crania which I have examined, the rami 

 of the lower jaw are disjoined at the sym- 

 physis ; and in the Opossum, both the rami of 

 the lower jaw and all the bones of the face are 

 remarkable for the loose nature of their con- 

 nection. 



Vertebral column. The vertebral column is 

 divisible in all the Marsupials into the usual 

 classes of cervical, costal, lumbar, sacral, and 

 caudal vertebrae. The cervical vertebrae inva- 

 riably present the usual number, seven, and 

 the usual character of the perforation of the 

 transverse process, or rather the presence of 

 the upper and lower transverse processes, and 

 the union of their outer extremities with a ru- 

 dimental rib. I found the cervical ribs of the 

 dentata distinct and unanchylosed in a mature 

 Perameles. In the Dasyures, Opossums, Ban- 

 dicoots, and Phalangers, the seventh cervical 

 vertebra has only the upper transverse process, 

 and consequently wants the character of the 

 perforation, as in many of the ordinary Mam- 

 malia. In the Petaurists, Koala, Wombat, 

 Potoroos, and Kangaroos, the seventh vertebra 

 is perforated like the rest. But in the Kan- 

 garoo both the dentata and atlas have the trans- 

 verse processes grooved merely by the vertebral 



