[695] Quart. Journ. Geol. Soc. vol. vi. part 2, p. 42.
BATRACHIANS.
VIII. Batrachians.—The reptiles termed Batrachians (from the Greek name for Frog) are characterized by the metamorphoses which they undergo in the progress of their development from the young to the adult state; the Frog, Toad, and Newt are familiar examples of this order. Their organs of aërial respiration consist of a pair of lungs; but in their young state they are provided with gills, supported, as in fishes, by cartilaginous arches. These organs disappear, in most species, when the animals arrive at maturity; but in a few genera, as the Siren and Proteus, they are persistent. The skeletons of these reptiles present corresponding modifications. The skull is, for the most part, much depressed, and the cerebral cavity small; it is united to the vertebral column by two distinct condyles, situated on the sides of the occipital or cranio-spinal aperture.[696] The vertebral column, in some genera (as, for example, in the common frog), is very short, and is reduced to eight or ten bones, the caudal vertebræ being fused into a long cylindrical style; but in the higher organised Batrachians the spine is composed of concavo-convex vertebræ, as in the Crocodile: in the lower type, as the Siren, Proteus, and Axolotl, the vertebræ are biconcave, as in numerous species of fossil Saurians. The ribs are merely rudimentary, being very short and few; a condition which has relation to the mode of reproduction in these animals, the eggs being accumulated and shed at once.[697] Some of the Batrachians are edentulous, but others have numerous small, conical, uniform, closely-arranged teeth, placed either in a single row, or aggregated like the rasp-teeth in fishes.[698]
[696] Saurians, like birds, have a single occipital condyle.
[697] See Dr. Roget’s Bridgewater Essay, p. 395.
[698] The variations in the dental system of these animals are given in Odontography, chap. ii. p. 187.
FOSSIL BATRACHIANS.
Batracholites; or fossil remains of Batrachians.—The skeletons, vestiges of the soft parts, and imprints of the feet of several genera of Batrachians occur in a fossil state in tertiary deposits, all of which, like the existing races, appear to belong to fresh-water or terrestrial species. In the pliocene or newer tertiary strata, on the banks of the Rhine, at Œningen, and in the papierkohle of the Eifel, several species of Frog, Toad, and Newt, have been discovered. Fossil frogs of a small species, very similar to the recent, occur in numbers in a dark shale, overlaid by basalt, in the vicinity of Bombay.[699]
[699] Quart. Geol. Journ. vol. iii. p. 221.
A celebrated fossil of this class is the gigantic Salamander (Cryptobranchus), three feet in length ([Lign. 243]), found at Œningen (see Wond. pp. 263, 580), which a German physician of some note (Scheuchzer) supposed to be a fossil man![700] and he described it in an essay, entitled "Homo diluvii testis et Theoscopos," as being the moiety, or nearly so, of a human skeleton, with the bones and flesh incorporated in the stone.[701] A fine example of this fossil Salamander is preserved in the British Museum (Petrif. p. 186).