DISTRIBUTION OF FAMILIES AND SUB-FAMILIES OF THE AMPHIBIA.
| Australian. | Neotropical. | Ne-arctic. | Palae-arctic. | Ethiopian. | Malagasy. | Indian. | Papuasian. | New Zealand. | ||
| West. | East. | |||||||||
| Amphiumidae | + | + | ||||||||
| Salamandridae | + | + | + | + | 1 | |||||
| Proteidae | + | + | ||||||||
| Sirenidae | + | |||||||||
| Apoda | + | + | + | |||||||
| Aglossa | + | + | ||||||||
| Discoglossidae | + | + | + | |||||||
| Pelobatidae | + | + | + | + | ||||||
| Bufonidae | + | + | + | + | + | + | + | + | ||
| Hylinae | + | + | + | 1 | 1 | |||||
| Amphignathodontinae | + | |||||||||
| Hemiphractinae | + | |||||||||
| Cystignathinae | + | + | 1 | |||||||
| Dendrophryniscinae | + | |||||||||
| Genyophryninae | ||||||||||
| Engystomatinae | + | 1 | + | + | + | |||||
| Dyscophinae | + | + | + | |||||||
| Dendrobatinae | + | × | ||||||||
| Raninae | + | + | + | + | + | + | + | + | ||
| Ceratobatrachinae | + | |||||||||
| 1 signifies the occurrence of only one species of an elsewhere numerous group. × Mantella, cf. p. [71] and p. [272]. | ||||||||||
CHAPTER IV
STEGOCEPHALI OR LABYRINTHODONTS–LISSAMPHIBIA–APODA
Sub-Class I. STEGOCEPHALI OR PHRACTAMPHIBIA
With a considerable amount of dermal armour, especially on the head.
The earliest known terrestrial four-footed creatures occur in the Carboniferous strata of Europe and North America. They and their immediate allies, which extend through the Permian into the Upper Trias, are now comprised under the name of Stegocephali, so called because the whole of the dorsal side of the cranium is covered, or roofed over, by dermal bones (στέγος, roof; κεφαλή, head). That these creatures, of which naturally only the skeletal parts are known, were not fishes, is shown by the typically pentadactyloid limbs; but to recognise them as Amphibia, and as distinct from Reptiles, is difficult, especially if the incipient Reptilia, which have sprung from some members of this Stegocephalous stock, are taken into account. However, they possess either two occipital condyles, or none, and their vertebrae are either pseudocentrous or notocentrous, but not gastrocentrous. Moreover, the whole skeletal organisation is still so ideally generalised, that it is easy to derive directly from it the arrangement prevailing in the Apoda and Urodela.
The vertebral column always comprises a well-developed, sometimes a very long tail. The vertebrae exhibit three types, two of which are fundamentally distinct, while the third is a further development of the second.
1. Lepospondylous and pseudocentrous.–The vertebra consists of a thin shell of bone surrounding the chorda dorsalis, and is composed of two pairs of arcualia, which meet each other, forming a suture, along the lateral side of the vertebra, both partaking in the formation of a transverse process which carries the rib.
2a. Temnospondylous.–The vertebra is composed of three pairs of units, which remain in a separate, unfused state. Two of them are dorsal arcualia, one of which tends to form the centrum of the vertebra, which then carries the neural arch.