CARBONIFEROUS AGE. 337 



The Amphibians were not of the naked-skinned kind of modern 

 time, but had scales, like the Ganoid Fishes, and also like most true 



Mammals. Unlike Fishes, as stated by Gill, they have a sternum; a shoulder-girdle, 

 represented by a scapula and its appendages; two lungs, instead of an air-bladder, each 

 with a special canal communicating with the pharynx; and the lower jaw articulated 

 with the skull by the intervention of a special bone, the os quadratum. They are of 

 low vital activity, with the temperature variable and in general directly related to that 

 of the surrounding medium. The vertebra? differ from those of Mammals, in being 

 convex and concave at the opposite ends, and in a few cases concave at both extrem- 

 ities, approximating, in this last case, to those of Fishes. The teeth, when set in sock- 

 ets, never have more than one prong of insertion, while, those of Mammals may have 

 two or more. They are of two types, which are so fundamentally distinct that they 

 require the division of the class into two sub-classes. 



I. Amphibians. — Breathing when young (or in the tadpole state) by means of gills, 

 and, with a few exceptions, undergoing a metamorphosis in which they become gill- 

 less. Heart with three cavities. 



II. Reptiles. — Having no gills at any period of life, and undergoing no metamor- 

 phosis. Heart with three or four cavities. 



I. Amphibians (Batrachians of most authors). 



In the Amphibians, the skeleton is distinguished by having (1) two occipital condyles, 

 for the articulation of the head with the bod}', one placed either side of the foramen ; 

 (2) the ribs very short, or rudimentary, or wanting; (3) the skull flat and usualty 

 broad, and of a loose and open structure. The body in living species is covered with a 

 soft skin, with sometimes minute scales, as in the Ccecilians. In an extinct group, there 

 are distinct scales ; and these species in this and other ways approach the true Reptiles. 



There are three tribes among living species, and a fourth of extinct species, if not 

 also a fifth. 



1. Ccecilians, or Snake-like Amphibians. — Body having the form of a snake ; no feet. 



2. Salamandroids, or Batrachia Urodela. — Body usually lizard-like, or resembling 

 in form a tadpole; having short legs, as in the Salamanders; sometimes, as in Siren, 

 only the two fore-feet developed ; ribs short. They graduate downward into species 

 that keep their gills through life, which, while perfect animals, are representatives of the 

 embryonic or young state of the higher Amphibians. In others, of intermediate grade, 

 the gill-opening is retained, but not the gills. But, in the large majority, the gills and 

 gill-openings both disappear. Some species, like the Siredon or Axoloil, of Mexico, 

 Siren and Necturus of the United States, and Proteus of the Adelsberg Cave, Carniola, 

 retain their gills through life. 



The Menopama of the Alleghany region, like some others, retains the gill-openings, 

 but not the gills ; the animals are large, broad and flat, sometimes over two feet long. 

 The Amphiuma of the Southern States also retains the gill-openings. The Megalo- 

 batrachus (or Sieboldia), of Japan, is closely related, although the gill-openings become 

 closed up: it is the largest of the existing tailed Amphibians, having a length exceed- 

 ing three feet. The fossil Andrias Scheuchzeri Tschudi, of the Tertiary, is related to it. 



The ordinary Salarnandrids axe. without gills or gill-openings, in the adult state. 



In most of the North American Salarnandrids, there are teeth on the vomer, and no 

 parotid gland; while the species of Europe want these vomerine teeth, and have parotid 

 glands. 



3. Batp.achoids (so named from the Greek Barpaxos, a frog), or Batrachia Anoura. 

 Body having four long legs (the hinder the longer) and no tail, as in the Toads and 

 Frogs. The teeth are small, and mostly on the roof of the mouth on the vomer, with 

 none in the lower jaw; the vertebra; are typically ten, but sometimes coalesce so as to 

 appear fewer, the apparent number seldom exceeding eight; the ribs are wanting. 



4. Labykixthodonts. — The species of this group of extinct Amphibians resemble 



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