THE SKELETON IN AMPHIBIA. THE TEETH. 169 



plates protect the anterior part of the thorax, and are closely 

 connected with the adjacent endoskeleton. They probably 

 represent the interclavicle and clavicles. Behind this buckler 

 numerous scutes are generally developed, which often cover 

 the whole ventral surface, and may cover the whole body. 



TEETH 1 . 



In Amphibia teeth are generally present on the maxillae, 

 premaxillae and vomers, and except in Anura on the dentaries ; 

 sometimes they occur on the palatines as in many Urodela, most 

 Labyrinthodontia, and the Gymnophiona; less commonly on the 

 pterygoids as in Menobranchus, Siredon, some Labyrinthodontia, 

 and Pelobates cultripes*, or on the splenials as in Siren and Meno- 

 branchus, or parasphenoid as in Pelobates cultripes, Spelerpes 

 belli and Batrachoseps. In some Anura such as Bufo and Pipa 

 the jaws are toothless. 



In Gymnophiona, Menobranchus, and Siredon, the teeth 

 are arranged in two concentric curved rows. The teeth of the 

 outer row are borne on the premaxillae and maxillae if present, 

 (the maxillae are absent in Menobranchus), the teeth of the 

 second row on the vomers and pterygoids in Menobranchus 

 and Siredon, and on the vomers and palatines in Gymnophiona. 

 In some Gymnophiona there is a double row of mandibular 

 teeth. The vomerine, palatine and parasphenoid teeth of all 

 forms are numerous and are not arranged in rows. 



The teeth of all living Amphibia are simple conical struc- 

 tures ankylosed to the bone, and consisting of dentine, coated 

 or capped with a thin layer of enamel. In the Labyrinthodontia 

 teeth of more than one size are sometimes present. The dentine 

 of the basal part of the larger teeth is in some genera very 

 greatly folded, causing the structure to be highly complicated. 

 These folds, the intervals between which are filled with cement, 



1 0. Hertwig. Ueber das Zahnsystem der Amphibien. Arch. mikr. 

 Anat. supplem. Bd. xi. 1875. 



- G. A. Boulenger, P. Z. S. 1890, p. 664. 



