In early anuran larvae the posterior wall of the nasal capsule is not developed. The olfactory nerves are exposed dorsally. Later paired, transversely located elements roof these nerves. They fuse and, later, produce, by downward growth, the walls of the olfactory canals. Laterally, the first functional partition between the future nasal capsule and orbit is the commissura quadratocranialis anterior. The ophthalmicus nerve runs across the dorsal surface of the commissura. In the course of further development, a new element (called the lamina orbitonasalis), arises anterolaterally to the commissura; consequently, the above mentioned nerve is enclosed in a canal betweeo the lamina orbitonasalis and the braincase. Meanwhile, the commissura becomes detached from the braincase and fixed to the lamina. Later another element, the epipraemandibulare, arises anterodorsally to the lamina; it encloses a branch of the ophthalmicus nerve in a canal. On the lateral end of the lamina orbitonasalis a further element arises: the processus maxillaris posterior. As the commissura later becomes detached even from the lamina, the processus ultimately represents the only connection of the palatoquadrate with the postnasal wall. Thus the postnasal wall, and adjacent parts of the palatoquadrate are of complex origin, though in adults they are a single unit. Comparison with those labyrinthodonts in which corresponding data are available reveals that the structure of their postnasal wall corresponds to certain larval stages of anurans. Thus the structure in adult anurans represents an evolutionary addition lacking in labyrinthodonts. For this reason, in the search for anuran ancestors one may compare adult labyrinthodonts not only with adult but also larval anurans.