297 



at its maximum of development in the Wombats: it is almost obsolete in Tarsipes. 

 In the Koala the process is compressed and directed backward, with the obtuse apex 

 only bending inward ; so that the characteristic flattening of the base of the ascending 

 ramus is feebly marked in this Marsupial. In the Thylacine, Sarcophile, and Dasyures 

 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 Opossums, and ascends in proportion to the 

 vegetable character of the diet. In all those Marsupialia which have few or very small 

 lower incisors, the horizontal rami of the jaw converge toward a point at the symphysis : 

 the angle of convergence is most open in the Wombats. 



§ 2. The Vertebral Column. — The columnar axis of the skeleton is divisible into 

 cervical, dorsal, lumbar, sacral, and caudal vertebrae. The cervical vertebras, seven in 

 number, show the usual character of the perforation of the transverse process, due to 

 the union of the outer extremities of par- and di-apophyses with a rudimental rib. I 

 found the pleurapophysis unanchylosed in the dentata of a mature Macrotis. In the 

 Dasyures, Opossums, Bandicoots, and Phalangers the seventh cervical vertebra has only 

 the upper transverse process (diapophysis), and consequently wants the character of the 

 perforation, as in many of the ordinary Mammalia. In the Petaurists, Koalas, Wombats, 

 Potoroos, and Kangaroos the seventh vertebra is perforated like the rest. 



The centrum of the atlas is anchylosed, as the ' odontoid process ' with that of the 

 axis. The neurapophyses have usually their ' central ' or lower ends united by un- 

 ossified sclerous tissue ; and the ; ring ' is interrupted below by a longitudinal vacuity 

 or fissure. 



In all the Marsupialia the spine of the dentata is well developed, in both the vertical 

 and longitudinal directions, but most so in the Virginian and Crab-eating Opossums, 

 where it increases in thickness posteriorly ; in these species also the third, fourth, and 

 fifth cervical vertebras have their spines remarkably long and thick. 



In the Koalas and Wombats a short obtuse process is given off from the under part 

 of the transverse process of the sixth cervical. In the Potoroos, Kangaroos, Petaurists, 

 Phalangers, Opossums, and Dasyures this process is remarkably expanded in the direc- 

 tion of the axis of the spine. In the Bandicoots corresponding processes are observed, 

 progressively increasing in size, in the fourth, fifth, and sixth cervical vertebrae. 



The number of the dorsal vertebrae is greatest in the Tasmanian Wombat, where it is 

 fifteen, with a corresponding number of pairs of ribs ; it is fewest in the Koala, which 

 has but eleven, with occasionally a short twelfth pair of ribs. In all the other genera 

 they are thirteen. 



In the Koala the length of the spine of the first dorsal hardly exceeds that of the 

 last cervical ; but in all other Marsupials the difference is considerable, the first dorsal 

 spine being much longer ; those of the remaining dorsal vertebrae progressively diminish 

 in length, and increase in breadth and thickness. They slope backward toward the 

 centre of motion, whicli in Mauge's Dasyure is shown to be at the ninth dorsal vertebra, 

 by the verticality of its spine, towards which both the preceding and succeeding spines 



