382
AMPHIBIA
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 subclass, 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 Linntean 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 the article “ Amphibia ” was written. When we turn to the definition given in that article (Ency. Brit. vol. i. p. 750), we find that one of the essential characters—“ two occipital condyles, the basi-occipital region of the skull either very incompletely, or not at all ossified ”—may require revision, if it be true, as held by some authors, that the bone on which the occipital condyles have been found most developed, in some labyrinthodonts (2), represents a large basi-occipital bone yielding the two knobs for the articulation of the skull, whilst the skull of the batrachians of the present day has lost the basi-occipital, and the condyles are furnished by the exoccipitals. More than this, some reptiles are now known to have the occipital condyle divided into two, and produced either by the basi-occipital (e.g., Amphisbcenidce, in some of which the double condyle resembles very closely that of the labyrinthodont Bothriceps), or by the exoccipitals (e.g., Uroplatidce). When we remember that the supposed condition of the occipital condyles was not very long ago thought sufficient to point to a possible direct descent of the mammals from the batrachians, we shall realize the full importance of the more correct information now available on this point. As a result of his researches on the anomodont reptiles and the Stegocephalia (3), as the extinct order that includes the wellknown labyrinthodonts is now called, we have had the proposal by Seeley (4) to place the latter with the reptiles instead of with the batrachians; whilst Credner (5), 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 (6). The outcome of our present knowledge points to the Stegocephalia, probably themselves derived from the Crossopterygian fishes (7) having yielded on the one hand the true batrachians (retrogressive series), with which they are to a certain extent connected through the Gaudata 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 (8). ’ 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 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 Dumeril in 1806 (Zool. Anal. pp. 90-94) these are termed “Anoures” and “ Urodfeles ” in French, Ecaudati and Caudati in Latin. When Dumeril’s pupil, Oppel, in 1811 (Ordn. Rept. p. 72), added the Cascilians, 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 (9). — Tailed, lacertiform, or serpentiform Fig- 1. — Upper view of Archegosaurus (Outlines after Credner.) pm,, batrachians, with the Decheni. prsemaxilla ; n, nasal; to, maxilla ; l, lacrytemporal region of the mal; pf, prsefrontal; /, frontal; j, jugal; ptf, postfrontal; p, parietal; st, supratemporal; skull roofed over by sq, squamosal; ptn, postorbital; qj, quadratopostorbital, squamosal, jugal; o, occipital; pt, post - temporal; q, and supratemporal quadrate. plates similar to the same bones in Crossopterygian fishes, and likewise with paired bones (occipitals and posttemporals) behind the parietals and supratemporals. A parietal foramen; scales or bony scutes frequently present, especially on the ventral region, which is protected further 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 Marsh (10) as Tinopus antiquus. Sundry remains from Belgium, as to the identification of which doubts are still entertained, have been regarded by Lohest (11) 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 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, JBurycormus) 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 Cope and some other recent authors have attempted to enforce. This is particularly evident in the case of the Stegocephalians ; and recent batrachians, tailed and tailless, show the mode of articulation of the vertebrae, whether amphiccelous, opisthoccelous, or procoelous, to be of but secondary systematic importance in dealing with these lowly vertebrates. The following division of the Stegocephalians into five sub-orders is therefore open to serious criticism ; but it seems on the whole the most natural to adopt in the light of our present knowledge.
