98 COMPAEATIVE DENTAL ANATOMY 



true teeth, appear. The teeth are ankylosed to 

 the bone like the teeth of fishes, which they much 

 resemble. 



In the common Frog, the teeth appear at the 

 time of the metamorphosis, when the tail is lost 

 and the legs appear, and the gills are aborted to 

 be replaced by lungs. The teeth appear on the 

 maxillary and premaxillary bones, but not on the 

 mandible, as the frog has no perceptible teeth on 

 the lower jaw. The teeth form a single row 

 around the margin of the upper jaw, — their points 

 projecting but little above the membrane, — 

 against which the lower jaw closes, there being no 

 lips. The teeth are ankylosed to the bones, each 

 one being perched upon a little pedestal of bone. 

 The successional teeth move up beneath the old 

 ones and push them off. The teeth are mere deli- 

 cate cones of hard dentin, with a thin layer of 

 enamel. 



The Toads are practically toothless, and have 

 no compensating structures. 



The Newts and Salamanders sometimes have 

 conical teeth that are bifurcated at the points and 

 are tipped with enamel. Some species have great 

 numbers of teeth, like the Teleostei fishes. 



The Sirens have horny sheaths on the jaws 

 (like the larval form of all the' Batrachians), and 

 teeth also on the vomers and on the sphenoidal 

 piece of the mandible. 



