- Skeleton of Right incisor very large and chisel-like, Hind-Foot of Koala (Phas- molars with prominent transverse colarctus cinereus), showing ridges, as in Macropus, but without stout opposable hallux, folthe longitudinal connecting ridge.
Of the metatarsals the fifth occurs as an embryonic vestige near the joint; the first is reduced to its distal portion, and is, with the hallux, shoved on to the inner and posterior side of the foot, at least in the majority of birds.
Reduction of the number of toes (the fifth shows no traces whatever, not even in Archaeopteryx) begins with the hallux, which is completely or partly absent in many birds; the second toe is absent in Struthio only.
Order Colymbiformes.-Plantigrade, nidifugous, aquatic. All toes webbed, fourth largest, hallux short; metatarsus laterally compressed; tibia with high, pyramidal crest.
Hallux absent or vestigial.
Front toes completely webbed; hallux very short or absent; feed chiefly on small aquatic invertebrates.
Front toes webbed; hallux small or absent.
Hallux vestigial or absent since Oligocene.
Hallux strong, with a large claw.
The number of toes is four, unless the hallux is more or less reduced.
Ignipalliatus, from Peru to Patagonia, more resembles the classical species; while P. andinus, the tallest of all, which lacks the hallux, inhabits the salt lakes of the elevated desert of Atacama, whence it extends into Chile and Argentina.
The hind-limb is typically avine, with intertarsal joint, distally reduced fibula, and the three elongated metatarsals which show already considerable anchylosis; reduction of the toes to four, with 2, 3, 4 and 5 phalanges; the hallux is separate, and as usual in recent birds posterior in position.