The Development of The Chondrocranium of Heleophryne Purcelli Sclater with special Reference to the Palatoquadrate and the Sound‐conducting Apparatus

A description of the later phases of the ontogeny of the chondrocranium of Heleophryne purcelli is given. Special attention has been given to the development of the sound‐conducting apparatus and to the structural changes of the palatoquadrate during metamorphosis. The operculum, the pars interna plectri and the pars media plectri are apparently of capsular origin, whereas the pars externa plectri and the anulus tympanicus, which develop from a common blasteme, appear to the be derivatives of the palatoquadrate. It is suggested that the infrapharyngohyal had been incorporated into the otic capsule during the phylogeny, and that it gives rise to the operculum and the pars interna et media plectri, as well as to the floor of the fossa fenestrae ovalis and the otic ledge of the adult. Similarly, the epihyal became incorporated into the posterior portion of the larval palatoquadrate (epimandibular), and gives rise to the pars externa plectri of the adult. The suprapharyngohyal is represented by the otic process and the lateral portion of the parotic crest. The anulus tympanicus is probably the homologue of the stylohyal of fishes. The suprapharyngomandibular and the infrapharyngo‐mandibular are both absent in the adult skull.