392 ANATOMY OF VEETEBRATES. 



single row, in each bone ; describing a semicircle, upon the pre- 

 maxillary, k, and maxillary, x, bones : a shorter parallel series is 

 supported on the vomerine bones, U The mandibular series is 

 received into the interspace of the two rows in the upper jaw. 



The Frogs {Ranaf have no teeth on the lower jaw ; but in 

 some species the alveolar edge of this bone is finely notched or 

 dentated, as in the horned Frogs ( Ceratophrys). Dactylethra has 

 maxillary teeth only ; Myohatrachus has but two horizontal pre- 

 maxUlary teeth. Both premaxillary and maxillary bones usually 

 support a long, close-set, single series of small, conical, hollow 

 teeth, of which the apices only jiroject beyond the external alveo- 

 lar ridge to which they are attached. A short transverse row of 

 similar but smaller teeth extends along the posterior border of each 

 vomer. Other dispositions of the vomerine teeth helj) to charac- 

 terise the genera of RanidcB, in a few of Avhich they are wanting ; 

 as, e.g., in Uperoleia, in the slender-armed Frogs (Leptohraclduni), 

 in Oxyglossus, and in some of the Tree Frogs (e.g. Eucnemis), in 

 which the roof of the mouth is edentulous. 



Amongst the most extraordinary examples of extinct reptUes 

 are those which are characterised by the labyrinthic modification 

 of the dental structure above described, and winch, with some 

 affinities to Saurians, combine characters which are essentially 

 those of the order Batrachia. In Labyrinthodon lejjtognuthus, the 

 upper jaw contains a single row of small teeth, about sixty in 

 number, anterior to which are three or four large conical tusks. 

 The apical two thirds of each tooth is smooth, but the basal third is 

 fluted and anchylosed to the outer wall of the socket. The osseous 

 roof of the mouth is principally composed of a pair of broad and 

 flat bones, homologous with the divided vomer in Batrachia, but of 

 much greater relative extent. Each bone supports anteriorly three 

 median small teeth and two outer larger ones, from which a longi- 

 tudinal row of small and equal-sized teeth is continued Ijackward 

 along the exterior margin of the vomer. The whole of this series 

 of vomerine teeth is nearly concentric with the maxillary teeth. 



In Lacertinc reptiles the examples of a row of palatal teeth are 

 rare, and, when present, it is short, and situated upon tlie i^tery- 

 goid Ijoncs, as in the Iguana and INIosasaur. In Batrachians the 

 most common disposition of the palatal teeth is a transverse row 

 placed at the anterior jiart of the divided vomer, as in Frogs, and the 

 Menopome. In the Ampliiumc, the vomerine teeth form a nearly 

 longitudinal scries along the outer margin of the i)alatlno bones. 



' V. pi. 02, lig. 10. - lb, jil. 62, fig. 10. 



