350 ANATOMY OF VERTEBRATES. 



pierced near its middle by the dental nerve and artery. The 

 surface of the external muscular depression bounded below by a 

 broad angular ridge, as above described, is entire in the Dasyures, 

 Opossums, Bandicoots, Petaurists, and Phalangers; but in the 

 Wombat the outer surface of the ascending ramus is directly 

 perforated by a round aperture immediately posterior to the com- 

 mencement of the dental canal : ^ the corresponding aperture is 

 of laro-er size in the Kangaroo. But in the Potoroos both the 

 external and internal depressions of the ascending ramus lead 

 to wide canals, or continuations of the wide depressions vvdiich 

 pass forward into the substance of the horizontal ramus, and soon 

 uniting into one passage, leave a vacant space in the intervening 

 bony septum. 



In the Thylacine, Ursine Dasyure, and the allied fossil carni- 

 vores called Phascolothere, Thylacoleo, and Plagiaulax,^ the con- 

 dyle of the lower jaw is placed low down, on a level mth the 

 molar series : it is raised a little above that level in the smaller 

 Dasyures and Opossums, and ascends in proportion to the vege- 

 table diet of the species. 



In all those Marsupials which have few or very small incisors 

 the horizontal rami of the jaw converge toward a point at the 

 symphysis. The angle of convergence is most open in the 

 Wombat, in which the symphysis is longest. The suture be- 

 comes obliterated in aged individuals. In other Marsupials, the 

 rami of the lower jaw are less firmly united at the symphysis ; 

 they permit independent movements of the right and left in- 

 cisors in the Kangaroos : 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 connections. 



C. Bones of the Limhs. — The scapula varies in form in the 

 different Marsupials. In the Petaurists it is a scalene triangle, 

 vdth the glenoid cavity at the convergence of the two longest 

 sides. In the Wombat, fig. 212, 5 1, it presents an oblong qua- 

 drate figure, the neck being produced from the lower half of 

 the anterior margin, and the outer surface being traversed diago- 

 nally by the spine, which in this species gradually rises to a full 

 inch above the plane of the scapula, and terminates in a long 

 narrow compressed acromion arching over the neck to reach the 

 clavicle. 



In the Koala (fig. 224), the superior costa does not run parallel 



' A bristle is represented passing through this aperture in fig. 220. 

 2 xvir.pp. 341, 353, figs. 113, 119, 173. 



