The Pelvic Girdle (Text-figure 5)

The most interesting feature of the pelvic girdle of Leiopelma is the presence of a cartilaginous, shield-shaped epipubis. A similar structure is possessed by Ascaphus (Noble, 1922, 1931; de Villiers, 1934), but the latter genus differs from Leiopelma by having also two posterior, subpelvic, skeletal rods which de Villiers has named the Nobelian bones and which are associated with the phallic organ: Xenopus is the only other Anuran genus apart from Leiopelma and Ascaphus to have an epipubis.

Although the epipubis of Leiopelma may, as de Villiers suggested, be a derivative of the linea alba which secondarily unites with the pubis, it has achieved complete continuity with the anterior ventral surface of the latter by the fourth week after hatching. It remains cartilaginous until maturity, but there is considerable evidence to show that in older specimens of Leiopelma hochstetteri at least it ultimately ossifies more or less completely. An epipubis in which two centres of ossification are present is shown in Text-figure 4 C, while Text-figure 4 A illustrates an epipubis which is almost completely ossified except for a posterior strip of cartilage. Frogs may be found in which the abdominal ribs are entirely cartilaginous, but the epipubis is mainly of bone. Like the abdominal ribs, the epipubis is partly

Text-Fig. 5—Pelvic girdle, from the left side. epu. epipubis is. ischlum il, illum pn. pubis