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to bullfrog papillar chamber

Hyloides branches

Hylids part I

Bufonids part I

Bufonids part II

Ranoides part I

Pipa pipa Surinam toad New World family: Pipidae

Bombina orientalis Asian fire-belly toad family: Bombinatoridae

Xenopus borealis Marsabit clawed frog Old World family: Pipidae

Scaphiopus bombifrons Plains spadefoot toad New World family: Scaphiopodidae

The AP branch of the VIIIth nerve approaches the papillar chamber from the ventro-medial side, then curves around the bottom of the chamber and up its caudo-lateral or lateral side to innervate the sensory surface on the chamber's ceiling. In all of the AP images on these pages, the nerve branch is transected, and only the lateral or caudo-lateral part of it is visible. The diaphragm or tectorial curtain is a thin extension of the tectorium that is attached entirely around the chamber wall directly adjacent to the curving nerve branch. Scanning electron microscope images usually show it in a highly-distorted state (Figure). In wet, fixed tissue, it can be seen in a less-distorted state (Figure from Lewis, Hecht, Narins 1992).

The tectorial corner is a small (sometimes pointed) extension of the sensory surface where it meets the tectorial curtain on the lateral or caudo-lateral side of the chamber ceiling Figure. In each of the images shown here the tectorial corner is labelled (TC).

During the course of evolution, as the caudal patch extended beyond the tectorial corner and its associated tectorial curtain, it took one of two routes. Either it continued rostro-medially, as it did here in Scaphiopus and Xenopus, or it turned and extended caudally, as it began to do in Pelobates fuscus and continued to do conspicuously in Sooglossus thomasetti and Gastrophryne olivacea page 1 The shape of the AP seen here for the Plains spadefoot is essentially the same as the AP shapes we observed in the other New-World spadefoot species we examined (Couch's spadefoot, Western spadefoot, Great-Basin spadefoot, and Eastern spadefoot).

Here we have a New-World pipid (Surinam toad) whose AP ended abruptly at the tectorial corner. In the other pipids we examined, which were Old-World forms (Xenopus laevis, X. borealis (shown here), and X. tropicalis), the AP continued rostromedially, well beyond the tectorial corner.

The AP of the bombinatorid, Bombina orientalis ended abruptly at the tectorial corner; in the other bombinatorid we examined, Bombina bombina, the European fire-bellied toad, the AP extended slightly beyond the tectorial corner.

One might conclude from these observations that the caudal patch of the early two-patch AP was being subjected to considerable evolutionary experimentation. The eventual resolution seems to have been extension in the caudal direction (rather than medial or rostro-medial), leading to the caudal extension, which usually terminated well caudal to the transected nerve branch, and which we observed in almost all of the neobatrachians we examined (approximately 50 species). We shall get back to the exceptions-- in a near-terminal branch of the Hyloides.