Similarly there are nine bones in a simple tarsus such as that of Salamandra. They form a proximal row of three, the tibiale, intermedium and fibulare, and a distal row of five, called respectively tarsale 1, 2, 3, 4, 5, beginning on the tibial side. Between the two rows there is a centrale as in the carpus, or there may be two.
The following names derived from human anatomy are commonly applied to the various carpal and tarsal bones:
| Carpus. | Tarsus. |
| radiale = scaphoid | tibiale} |
| intermedium = lunar | intermedium } astragalus |
| ulnare = cuneiform | fibulare = calcaneum |
| centrale = central | centrale = navicular |
| carpale 1 = trapezium | tarsale 1 = internal cuneiform |
| "2 = trapezoid | "2 = middle " |
| "3 = magnum | "3 = external " |
| "4 } | "4 } |
| "5 } = unciform | "5 }= cuboid |
Note. The above is the view commonly accepted concerning the homology of the carpal and tarsal bones. But with regard to the proximal row of tarsal bones there is difference of opinion. All anatomists are agreed that the calcaneum is the fibulare and that the intermedium is contained in the astragalus, but while the majority regard the astragalus as the fused tibiale and intermedium, Baur considers that a small bone found on the tibial side of the tarsus in Procavia, many Rodents, Insectivores, and the male Ornithorhynchus, is the vestigial tibiale, and regards the astragalus as the intermedium alone[13]. He also considers that the mammalian scaphoid represents a centrale.
Modifications in the positions of the limbs[14].
In their primitive position the limbs are straight and are extended parallel to one another at right angles to the axis of the trunk. Each limb then has a dorsal surface, a ventral surface, an anterior or pre-axial edge, and a posterior or postaxial edge.
In the anterior limb the radius and the pollex are pre-axial, the ulna and the fifth finger are postaxial. In the posterior limb the tibia and the hallux are pre-axial, the fibula and the fifth toe are postaxial. The Cetacea and various extinct reptiles, such as Ichthyosaurus and Plesiosaurus, have their limbs in practically this primitive position.
The first modification from it is produced by the bending ventrally of the middle segments of both limbs upon the proximal segments, while the distal segment is bent in the opposite direction on the middle segment. Then the ventral surfaces of the antibrachium and crus come to look inwards, and their dorsal surfaces to look outwards. The brachium and manus, thigh and pes still have their dorsal surfaces facing upwards and their ventral surfaces facing downwards as before, and the relations of their pre- and postaxial borders remain as they were. Many Amphibians and Reptiles, such as tortoises, carry their limbs in this position.
In all higher vertebrates, however, a further change takes place, each limb is rotated as a whole from its proximal end, the rotation taking place in opposite directions in the fore and hind limbs respectively. The anterior limb is rotated backwards from the shoulder, so that the brachium lies nearly parallel to the body, and the elbow points backwards, the antibrachium downwards, and the manus backwards; the pre-axial surface of the whole limb with the radius and pollex now faces outwards, and the postaxial surface with the ulna and fifth finger now faces inwards. In the Walrus and, to a certain extent, in the Sea lions the anterior limb remains throughout life in this position. The posterior limb is also rotated, but the rotation in this case takes place forwards, so that the thigh lies nearly parallel to the body, the knee-joint pointing forwards; the crus downwards and the pes forwards. The pre-axial surface of the whole limb with the tibia and hallux looks towards the middle of the body, the postaxial surface with the fibula and fifth toe looks outwards. This is the position in which the hind limb is carried in nearly all mammals.