Chapter V: Front Matter (5)

BATRACHIA. The arguments adduced by T.H. Huxley, in his article on this subject in the ninth edition of the _Encyclopaedia Britannica_, for applying the name Amphibia to those lung-breathing, pentadactyle vertebrates which had been first severed from the Linnaean Amphibia by Alexandre Brongniart, under the name of _Batrachia_, have not met with universal acceptance. Although much used in text-books and anatomical works in Great Britain and in Germany, the former name has been discarded in favour of the latter by the principal authors on systematic herpetology, such as W. Peters, A. Gunther 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).

(Outlines after Gredner.)

pm, Praemaxilla. st, Supratemporal.
n, Nasal. sq, Squamosal.
m, Maxilla. pto, Postorbital.
l, Lachrymal. qj, Quadrato-jugal.
pf, Praefrontal. o, Occipital.
f, Frontal. pt, Post-temporal.
j, Jugal. q, Quadrate.
ptf, Postfrontal.
p, Parietal.]

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. Dumeril in 1806 (_Zool. Anal_. pp. 90-94) these are termed "Anoures" and "Urodeles" in French, _Ecaudati_ and _Caudati_ in Latin. When Dumeril'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.