GENERAL STRUCTURE AND ORDERS. 



1023 



Reptilian ; and we may probably regard the Anomodont Reptiles 

 as having taken their origin from a group closely allied to the Laby- 

 rinthodonts, if not actually from this order. As regards the sub- 

 divisions of the order there is still considerable uncertainty, and all 

 such divisions must consequently be regarded, as more or less pro- 

 visional. Dr Fritsch has, indeed, proposed to range the families 

 under four series or suborders, according to the external contour of 

 the body and the nature of the vertebral column ; this grouping 

 being provisionally adopted in the present work, with some emenda- 

 tion of nomenclature. 



Suborder i. Branchiosauria. — In this suborder the external 

 appearance approaches that of the modern Salamanders. The ver- 

 tebrae have centra composed of a single piece, which retains traces 

 of the notochord ; the ribs are short and straight ; and the neural 

 canal is dilated in the middle of each vertebra. The teeth are 

 simple in structure, and internal gills were developed in the young. 

 Some authorities include the next two groups in the present sub- 

 order under the name of Lepospondyli. 



Family Protritonid^e. — The Branchiosauridce of Dr Fritsch, 

 being founded on a name which is apparently a synonym, may be 

 better known as the Protrito?iid<z. They are characterised by the 

 great breadth of the skull (fig. 950), and the smooth teeth. Typi- 

 cally the palatines, according to Dr Credner, are small transversely 

 elongated bones lying in the 

 anterior part of the skull, and 

 not joining the maxillae ; this 

 arrangement being similar to 

 that found in the Ecaudata. 

 The type genus Protriton 

 (Branchiosaurus or Pleuron- 

 urd) is found abundantly in 

 the Permian of the Continent ■ 

 and its development has been 

 fully worked out by Dr Cred- 

 ner from the study of a large 

 number of specimens of all 

 ages. The specimen shown 

 in fig. 953 exhibits the nearly 



entire skeleton of a small individual, while the details of the cra- 

 nial structure are exemplified in the greatly enlarged skull shown 

 in fig. 950. 



According to the observations of Dr H. Credner, it appears that 

 the youngest specimens known were 25 mm. in length, in which stage 

 the creature was aquatic, and breathed by gills, which were supported 

 by four pairs of arches. By the time they attained a length of from 60 



Fig. 953. — Ventral aspect of the nearly entire 

 skeleton of a young individual of Protriton 

 petrolei; from the Permian of France. (After 

 Gaudry.) 



