This group includes the herbivorous Marsupials. The incisors are as a rule three above, but one only in the Wombats. Below
is one strong pair, with occasionally one or two rudimentary incisors. The upper canines, if present, are not large. The molars are tuberculate or ridged. All Marsupials (except the Wombats) to some extent, and the Macropods especially, are characterised by the prolongation of the tubes of the dentine into the clear enamel. The significance of this fact is, however, lessened by the fact that the same penetration of the enamel by dentinal tubes occurs in the Jerboa, the Hyrax, and some Shrews. The feet have two syndactylous toes,[[72]] less marked in the Wombats than in the Kangaroos and Phalangers.
Fig. 63.—Skull of Wombat (Phascolomys wombat). (Lateral view.) ang, Angular process; cond, condyle of mandible; ext.aud, opening of bony auditory meatus; ex.oc, exoccipital; ju, jugal; lcr, lachrymal; max, maxilla; nas, nasal; p.max, premaxilla; sq, squamosal; ty, tympanic. (From Parker and Haswell's Zoology.)
This order is mainly Australian at the present day, using the term of course in the "regional" sense (see p. [84]); the only exception indeed to this statement is the occurrence of the genus Caenolestes in South America. But it is now known that Diprotodont Marsupials formerly existed in the same part of the world.
Fig. 64.—Bones of right foot of Kangaroo (Macropus bennetti). a, Astragalus; c, calcaneum; cb, cuboid; e3, ento-cuneiform; n, navicular; II-V, second to fifth toes. (From Flower's Osteology.)
Fig. 65.—Skeleton of Wallaby (Macropus ualabatus). The scapula is raised somewhat higher than in nature. The end of the tail is omitted. The head of the femur has been separated from the acetabulum. acet, Acetabulum; acr, acromion process; ast, astragalus; cal, calcaneum; cbd, cuboid; chev, chevron-bones; cl, clavicle; cun, cuneiform of carpus; epi, epipubis; fb, fibula; fem, femur; hd, head of femur; hu, humerus; il, ilium; isch, ischium; obt, obturator-foramen; orb, orbit; pis, pisiform; pub, pubis; rad, radius; rb1, first rib; rb13, last rib; sc, scapula; st, sternum; tb, tibia; troch, great trochanter of femur; uln, ulna; unc, unciform; IV, fourth toe. (From Parker and Haswell's Zoology.)