[Illustration: FIG. 43.—Skeleton of right hind foot of _Chœropus castanotis_. _c_, Calcaneum; _a_, astragalus; _cb_, cuboid; _n_, navicular; _c³_, ectocuneiform; II and III, the conjoined second and third digits; IV, the large and only functional digit; V, the rudimentary fifth digit.] _Chœropus._[51]—Dentition generally resembling that of _Perameles_, but the canines are less developed, and in the upper jaw two-rooted. Limbs very slender; posterior nearly twice the length of the anterior. Fore feet with the functional toes reduced to two, the second and third, of equal length, with closely united metacarpals and short, sharp, slightly curved, compressed claws. First toe represented by a minute rudiment of a metacarpal bone; the fourth by a metacarpal and two small phalanges without a claw, and not reaching the middle of the metacarpal of the third; fifth entirely absent. Hind foot (Fig. 43) long and narrow, mainly composed of the strongly developed fourth toe, terminating in a conical pointed nail, with a strong pad behind it; the hallux absent or represented by a rudimentary metatarsal; the remaining toes completely developed, and with claws, but exceedingly slender; the united second and third reaching a little way beyond the metatarso-phalangeal articulation of the fourth; the fifth somewhat shorter. Tail not quite so long as the body, and covered with short hairs forming a slight crest. Ears large and pointed, and folded down when the animal is at rest. Fur soft and loose. Vertebræ: C 7, D 13, L 6, S 1, C 20. Skull short and wide, with a small and single bulla, and a contraction of the muzzle at the third premolar. The only known species of this genus (Fig. 44), chiefly remarkable for the singular construction of its limbs, is an animal about the size of a small Rat, found in the interior of the Australian continent. Its general habits and food appear to resemble those of the other _Peramelidæ_. It was first described as _C. ecaudatus_ by Ogilby from a mutilated specimen, but the specific name was afterwards changed, as being inappropriate, by Gray to _castanotis_. _Suborder_ DIPROTODONTIA. For the leading characters of this group, see page 132. _Family_ PHASCOLOMYIDÆ.