Fig. 31. A, Right Antibrachium and Manus of a larval Salamander (Salamandra maculosa) (after Gegenbaur).
B, Right Tarsus and adjoining bones of Molge sp. (after Gegenbaur).

1. radius.11. tibia.
2. ulna.12. fibula.
3. radiale.13. tibiale.
4. intermedium.14. intermedium.
5. ulnare.15. fibulare.
6. centrale.16. centrale.
7. carpale 2.17. tarsale 1.
8. " 3.18. tarsalia 4 and 5 fused.
9. " 4.I. II. III. IV. V. digits.
10. " 5.

In the great majority of Amphibia while one digit, probably the first, is absent, the other four digits are well developed. In the forms however with degenerate limbs like Amphiuma, Siren and Proteus the number of digits is still further reduced. In Siren there are three or four, in Proteus three, and in Amphiuma two or three digits in the manus.

In Anura the pollex is represented only by a short metacarpal. There are sometimes traces of a prepollex. The carpus often has two centralia and the intermedium is absent.

In Labyrinthodontia the limbs are generally very simple and resemble those of Urodela. In some forms, however, the manus differs from that of all living Amphibia in possessing five well-developed digits.

Pelvic girdle.

The simplest Amphibian pelvis is that of some of the Labyrinthodontia; thus in Mastodonsaurus it consists dorsally of a short broad ilium placed vertically and attached to the sacrum, and ventrally of a small pubis and of a large ischium meeting its fellow in the middle line. In some Labyrinthodonts the pubes as well as the ischia meet in a ventral symphysis, and in many there are no obturator foramina. In Siren, Gymnophiona and some Labyrinthodontia the pelvic girdle and limbs are absent.

In Urodela the ventral element of the pelvis on each side forms a flat plate which meets its fellow of the opposite side. The anterior part of the plate, representing the pubis, generally remains cartilaginous throughout life; the posterior part representing the ischium is in almost every case well ossified. Attached to the anterior end of the pubes there is an unpaired bifid cartilaginous structure, the epipubis. The ilia are vertically placed.

In most Anura the pelvis is peculiarly modified in correlation with the habits of jumping. The long bone generally called the ilium is placed horizontally and is attached at its extreme anterior end to the sacrum. The ischium is ossified and distinct. Ventrally in front of the ischium there is a tract of unossified cartilage which is often regarded as the pubis. In Xenopus, however, the bone corresponding to the ilium of the Frog is seen to ossify from two centres, one forming the ilium, the other, which lies at the symphysis, being apparently the pubis. This makes it probable that the so-called ilium of the Frog is really to be regarded as an ilio-pubis, and renders the homology of the cartilaginous part uncertain, but it probably corresponds to the acetabular bone of mammals. In Xenopus also there is a minute epipubis similar to that of Urodeles.

Posterior limb.