[Illustration: FIG. 10.—Mandible of _Labidosaurus_, a cotylosaur reptile: _A_ from within; _B_ from without. The coronoid (_cor_) is a single bone, but extends far forward. The splenial (_sp_) is also a single bone, replacing the two of the amphibians. The _prearticular_ (_pa_) is narrower, and the angular (_ang_) appears broadly on the inner side. The dentary (_d_) is much larger and the surangular (_sa_) is distinct. The articular (_art_) is small.] [Illustration: FIG. 11.—Mandible of _Alligator_, a modern, highly specialized reptile, from within. The coronoid (_cor_) is small and is situated far back; the splenial (_sp_) does not extend to the symphysis; the prearticular (_pa_) has disappeared, or has fused with the angular (_an_) or articular (_art_). The dentary (_d_) has become the chief bone of the mandible.] The teeth of reptiles are of much less importance, as a rule, in the determination of relationships than are the teeth of mammals. Rarely are their shapes of specific, and often not of generic, importance, though their number and relative sizes may be. The teeth of mammals, as a rule, are forty-four or less in number, and they are always inserted in distinct sockets in the jaw bones. Among reptiles they are indefinite in number, and may be attached to any of the bones of the palate and sometimes also to the coronoid of the mandibles. Furthermore, except in those reptiles related to the immediate ancestors of the mammals, they are alike or nearly alike in the jaws, that is, homodont, not distinguishable into incisors, canines, and molars. They may be inserted in separate sockets (thecodont), in grooves, or simply be co-ossified to the surface of the bone (acrodont). And they are usually reproduced indefinitely by new teeth growing at the side of the base or below them. More usually they are pointed and curved; sometimes they are flattened, with sharp cutting edges in front and behind in the more strictly carnivorous reptiles; in those of herbivorous habits they are more dilated and roughened on the crown, not pointed; in not a few they are low, broad, and flat and are used only for crushing the hard shells of invertebrates. With the very few exceptions among certain dinosaurs, they never have more than one root for attachment. The evolutional tendency for reptiles, as for the mammals, is to loose teeth, especially those of the palate. Among living reptiles it is only the most primitive types, such as the lizards, snakes, and the tuatera, which have teeth on the palatal bones, and in none are there teeth on the vomers, as was the rule in the ancient reptiles. The lizards may have them on pterygoids and palatines, and the tuatera has them on the palatines only. There may be as many as eighty on each jaw, above and below, and hundreds of smaller ones on the palate, or they may be reduced in number to five or six, or even to a single one; some reptiles, like the turtles and later pterodactyls, have none.