The differences of these beaked lizards from the true lizards are especially noticeable in the skull, and more especially in the arrangement of the bones which give articulation to the lower jaws (Fig. 8). In the lizards and snakes the quadrate bone is loosely articulated at its upper end with the cranium, and has no inferior bar or arch connecting its lower end with the jugal and the back part of the upper jaw. _Sphenodon_, on the contrary, has the quadrate bone firmly fixed to its adjacent bones at both ends, and is quite immovable. The vertebrae are biconcave like those of all early reptiles, not concavo-convex as are the vertebrae of most other living reptiles. The intercentra or hypocentra, little wedge-shaped bones between the centra below, are more persistent in _Sphenodon_ than in any other living land animals except the gecko lizards. Upon the whole the tuatera is the most old-fashioned of living reptiles, and in consequence it has nearly lost out in competition with new things. [Illustration: FIG. 85.—_Sphenodon punctatum_, or tuatera. (From specimen in the Yale University museum.)] With these living tuateras we have nothing further to do, since they are land animals, living about the beaches of the New Zealand islands, and only occasionally venturing into the water, hiding from their enemies in the holes in the rocks. But, from some of their antecedents, from some of their direct forbears perhaps, there have gone off at different times various branches, whose descendants wandered into foreign lands or into foreign places, and lived and flourished for a brief time and then became extinct. Some of these went down into the water and became more or less aquatic in habit; some, indeed, changed their forms and habits so greatly that they are often, perhaps rightly, segregated into different orders. Whether or not they should be called Rhynchocephalia matters little, however. It is merely a matter of opinion as to how great the changes should be in order to entitle the offspring to a genealogical tree all its own. Of these branches there are two, whose relationships seem to be definite, the Choristodera and Thalattosauria, though there is more doubt about the latter than the former. A third group, that included _Pleurosaurus_, seems, from more recent discoveries, to belong to a different line of descent and has been described under the Protorosauria. In the direct line of ancestry there is no known form that was distinctly aquatic. The oldest known of these, perhaps, is that shown in Fig. 86, _Sapheosaurus_ from the Jurassic of Solenhofen. Its resemblance to the modern tuatera is great, and doubtless its habits were very similar, though its rather long tail and rather short neck possibly indicate subaquatic habits. [Illustration: FIG. 86.—_Sapheosaurus_, an Upper Jurassic rhynchocephalian. (After Lortet.)] CHORISTODERA