on systematic herpetology, such as W. Peters, A. Günther and E.D. Cope, and their lead is followed in the present article. Bearing in mind that Linnaeus, in his use of the name Amphibia, was not alluding to the gill-breathing and air-breathing periods through which most frogs and newts pass in the course of their existence, but only wished to convey the fact that many of the constituents of the group resort to both land and water (e.g. crocodiles), it seems hard to admit that the term may be thus diverted from its original signification, especially when such a change results in discarding the name expressly proposed by Brongniart to denote the association which has ever since been universally adopted either as an order, a sub-class or a class. Many authors who have devoted special attention to questions of nomenclature therefore think Reptilia and Batrachia the correct names of the two great classes into which the Linnaean Amphibia have been divided, and consider that the latter term should be reserved for the use of those who, like that great authority, the late Professor Peters, down to the time of his death in 1883, would persist in regarding reptiles and batrachians as mere sub-classes (1). However extraordinary it may appear, especially to those who bring the living forms only into focus, that opposition should still be made to Huxley’s primary division of the vertebrates other than mammals into Sauropsida (birds and reptiles) and Ichthyopsida (batrachians and fishes), it is certain that recent discoveries in palaeontology have reduced the gap between batrachians and reptiles to such a minimum as to cause the greatest embarrassment in the attempt to draw a satisfactory line of separation between the two; on the other hand the hiatus between fishes and batrachians remains as wide as it was at the time Huxley’s article Amphibia (Encyclopaedia Britannica, 9th ed.) was written.
The chief character which distinguishes the Batrachians from the reptiles, leaving aside the metamorphoses, lies in the arrangement of the bones of the palate, where a large parasphenoid extends forwards as far or nearly as far as the vomers and widely separates the pterygoids. The bones which bear the two occipital condyles have given rise to much discussion, and the definition given by Huxley in the previous edition—“two occipital condyles, the basi-occipital region of the skull either very incompletely or not at all ossified”—requires revision. Some authors have held that the bone on which the occipital condyles have been found most developed in some labyrinthodonts (2) represents a large basi-occipital bearing two knobs for the articulation with the first vertebra, whilst the skull of the batrachians of the present day has lost the basi-occipital, and the condyles are furnished by the exoccipitals. On the other hand, some reptiles have the occipital condyle divided into two and produced either by the basi-occipital or by the exoccipitals. But the recent find of a well preserved skull of a labyrinthodont (Capitosaurus stantonensis) from the Trias of Staffordshire has enabled A.S. Woodward (3) to show that, in that form at any rate, the condyles are really exoccipital, although they are separated by a narrow basi-occipital. It is therefore very probable that the authors quoted in (2) were mistaken in their identification of the elements at the base of the foramen magnum. The fact remains, however, that some if not all of the stegocephalous batrachians have an ossified basi-occipital.
As a result of his researches on the anomodont reptiles and the Stegocephalia (4), as the extinct order that includes the well known labyrinthodonts is now called, we have had the proposal by H.G. Seeley (5) to place the latter with the reptiles instead of with the batrachians, and H. Gadow, in his most recent classification (6), places some of them among the reptiles, others being left with the batrachians; whilst H. Credner, basing his views on the discovery by him of various annectent forms between the Stegocephalia and the Rhynchocephalian reptiles, has proposed a class, Eotetrapoda, to include these forms, ancestors of the batrachians proper on the one hand, of the reptiles proper on the other. Yet, that the Stegocephalia, notwithstanding their great affinity to the reptiles, ought to be included in the batrachians as commonly understood, seems sufficiently obvious from the mere fact of their passing through a branchiate condition, i.e. undergoing metamorphosis (7). The outcome of our present knowledge points to the Stegocephalia, probably themselves derived from the Crossopterygian fishes (8), having yielded on the one hand the true batrachians (retrogressive series), with which they are to a certain extent connected through the Caudata and the Apoda, on the other hand the reptiles (progressive series), through the Rhynchocephalians and the Anomodonts, the latter being believed, on very suggestive evidence, to lead to the mammals (9).
|Fig. 1.—Upper view of Archegosaurus Decheni.|
(Outlines after Gredner.)
|pm, Praemaxilla.||p, Parietal.|
|n, Nasal.||st, Supratemporal.|
|m, Maxilla.||sq, Squamosal.|
|l, Lachrymal.||pto, Postorbital.|
|pf, Praefrontal.||qj, Quadrato-jugal.|
|f, Frontal.||o, Occipital.|
|j, Jugal||pt, Post-temporal.|
|ptf, Postfrontal.||q, Quadrate.|
The division of the class Amphibia or Batrachia into four orders, as carried out by Huxley, is maintained, with, however, a change of names: Stegocephalia, for the assemblage of minor groups that cluster round the Labyrinthodonta of R. Owen, which name is restricted to the forms for which it was originally intended; Peromela, Urodela, Anura, are changed to Apoda, Caudata, Ecaudata, for the reason that (unless obviously misleading, which is not the case in the present instance) the first proposed name should supersede all others for higher groups as well as for genera and species, and the latter set have the benefit of the law of priority. In the first subdivision of the batrachians into two families by C. Duméril in 1806 (Zool. Anal. pp. 90-94) these are termed “Anoures” and “Urodeles” in French, Ecaudati and Caudati in Latin. When Duméril’s pupil, M. Oppel, in 1811 (Ordn. Rept. p. 72), added the Caecilians, he named the three groups Apoda, Ecaudata and Caudata. The Latin form being the only one entitled to recognition in zoological nomenclature, it follows that the last-mentioned names should be adopted for the three orders into which recent batrachians are divided.
I. Stegocephalia (10).—
Tailed, lacertiform or serpentiform batrachians, with the temporal region of the skull roofed over by postorbital, squamosal, and supratemporal plates similar to the same bones in Crossopterygian fishes, and likewise with paired dermal bones (occipitals and post-temporals) behind the parietals and supratemporals. A parietal foramen; scales or bony scutes frequently present, especially on the ventral region, which is further protected by three large bony plates—interclavicle and clavicles, the latter in addition to cleithra.
Extinct, ranging from the Upper Devonian to the Trias. Our knowledge of Devonian forms is still extremely meagre, the only certain proof of the existence of pentadactyle vertebrates at that period resting on the footprints discovered in Pennsylvania and described by O.C. Marsh (11) as Tinopus antiquus. Sundry remains from Belgium, as to the identification of which doubts are still entertained, have been regarded by M. Lohest (12) as evidence of these batrachians in the Devonian. Over 200 species are now distinguished, from the Carboniferous of Europe and North America, the Permian of Spitsbergen, Europe, North America and South Africa, and the Trias of Europe, America, South Africa, India and Australia. The forms of batrachians with which we are acquainted show the vertebral column to have been evolved in the course of time from a notochordal condition with segmented centra similar to that of early bony ganoid fishes (e.g. Caturus, Eurycormus), to biconcave centra, and finally to the socket-and-ball condition that prevails at the present day. However, owing to the evolution of the vertebral column in various directions, and to the inconstant state of things in certain annectent groups, it is not possible, it seems, to apply the vertebral characters to taxonomy with that rigidity which E. D. Cope and some other recent authors have attempted to enforce.