More remarkable than the above are the little Flying Dragons (Draco) of the East Indies and Indian Archipelago. In these singular little Lizards there is a broad membranous expansion on each side, formed by a fold of the integument, supported upon the five or six posterior or false ribs, which run straight out from the spinal column (fig. 282). By means of these lateral expansions of the skin, the Draco can take long flying leaps from tree to tree, and can pursue the insects on which it feeds; but the lateral membranes simply act as parachutes, and there is no power of true flight, properly so called.

The Geckotida form a large family of Lizards, comprising a great number of species, occurring in almost all parts of the world between and near the tropics. The tongue is wide, flat, scarcely notched at its free extremity, and hardly at all protrusible. The eyes are large, mostly with extremely short lids, the pupil mostly vertical and linear, but sometimes circular. The vertebræ are amphicolous. The teeth are numerous, small, compressed, and implanted on the inner edge of the jaw. The nails (when present) are mostly hooked and retractile, and the toes are furnished below with imbricated plates or with adhesive discs. The animal is generally capable of

running on the smoothest surfaces, or suspending itself backdownwards. They feed on insects, and are found in abundance in the warmer parts of both the Old and New Worlds.

Another remarkable family of Lacertilians is that of the

Chameleontida, containing, among other species, the familiar little Chamaleo Africanus, which occurs abundantly in the north of Africa and in Egypt, and is so well known for its power of changing its colour under irritation or excitement. In this genus the eye (fig. 284) is of large size, and is covered

by a single circular lid, perforated centrally by a small aperture, by which the rays of light reach the pupil. The Chameleon is naturally a sluggish animal, but it catches its food, consisting of insects, by darting out its long, fleshy, and glutinous tongue-an operation which it effects with the most extraordinary rapidity.

The tail in the Chameleons is round and prehensile, the body compressed, and the skin like shagreen. The tongue is long, vermiform, club-shaped in front, and very extensile. The toes are adapted for the arboreal life and scansorial habits of the animal, being so arranged as to form two equal and opposable sets. The lungs are excessively voluminous. The Chameleons are exceedingly sluggish and slow in their movements, and are confined to the warmer parts of the Old World.

The last group of living Lizards which requires notice is that of the Rhynchocephalia, a group comprising only the curious genus Hatteria or Sphenodon, which is so aberrant in its characters that this section may well be regarded as a suborder of Lacertilia. Only one species (H. punctata) of this genus is known, and it inhabits New Zealand.

In this singular form (fig. 285) the vertebrae are amphicœlous, and some of the ribs bear "uncinate processes" similar to those of Birds. The quadrate bone is not movable, and is united by suture with the skull. The teeth are completely amalgamated by anchylosis with the jaws, and are developed in the mandible,

præmaxillæ, maxillæ, and in a longitudinal series upon the palatine bones. The præmaxillary teeth are two in number. and are of large size and scalpriform in shape. The serrated

edge of the mandible is received in the groove between the palatine teeth and the cutting edges of the maxillæ, the alveolar borders of which are hard and as highly polished as the teeth themselves, the function of which they discharge when the latter are ground down in advanced age. Unlike any other Saurian, Hatteria is devoid of any copulatory organ.

DISTRIBUTION OF LACERTILIA IN TIME.-It is hardly possible, with our present knowledge, to speak very positively as to the exact range of the Lacertilia in time. This uncertainty arises from two causes-firstly, that there is some doubt as to the exact age of some deposits which have yielded Lacertilian remains; and, secondly, that the affinities of some extinct Reptiles are a matter of considerable question. Upon the whole, the oldest known Lacertilian would appear to be the Protorosaurus of the Middle Permian rocks; though good authorities have placed this form in the Crocodilian group of the Thecodontia. Protorosaurus attained a length of between five or six feet, and differs from all existing Lizards in having its teeth implanted in distinct sockets-this being a Crocodilian character. In other respects, the Permian reptile approximates closely to the living Monitors (Varanida), and its slightly cupped vertebræ would lead to the belief that it was aquatic in its habits. Both pairs of limbs were present, both pentadactylous, and constructed on the type of the limbs of the typical Lizards.

In rocks known or supposed to be of Triassic age, several Lacertilian reptiles have been discovered, of which the most important are Telerpeton, Hyperodapedon, and Rhynchosaurus,

of which the last is sometimes referred to the group of the Anomodontia, to be subsequently spoken of.

a

b

In the Jurassic period, the remains of Lacertilians are not unknown, but call for little special notice. Several forms of little importance have been described from the Middle Oolites. In the fresh-water strata of the Purbeck series (Upper Oolites), occur the remains which have been referred to the genera Nuthetes, Macellodon, Saurillus, and Echinodon. These are, perhaps, the first traces in the stratified series of remains, the affinities of which to the typical Lacertida cannot be disputed. In the Cretaceous rocks occur the singular Lacertilians which form the group of the "Mosasauroids." These remarkable Reptiles were of gigantic size, Mosasaurus princeps being believed to have attained the enormous length of not less than seventy-five feet. The teeth of these reptiles are long, conical, and slightly curved; but they are anchylosed to the jaw, and are not sunk into distinct sockets as in the living Crocodiles. The vertebræ are procoelous. From the shortness of the humerus, and the indications that the vertebral column was unusually flexible, and that the tail was laterally compressed, it was early conjectured that the Mosasauroids were marine and aquatic in their habits. This conjecture has been raised to the rank of a certainty by the discovery that the fore and hind limbs of the Mosasauroids were in the form of fin-like paddles, resembling the flippers of whales in general structure, and in having the digits distinct and only conjoined by integument (fig. 286). There can therefore be no doubt that Mosasaurus-like the living Amblyrhynchus was aquatic in its habits, and frequented the sea-shore, coming, in fact, only occasionally to the land. Professor Marsh has also recently shown that some species possess bony dermal scutes, thus rendering their Lacertilian affinities somewhat dubious.

88

Fig. 286.-Right anterior paddle of Les-
tosaurus simus, one-twelfth of the
natural size. (After Marsh.) a Scap-
ula; b Coracoid; c Humerus; d Ra-
dius; e Ulna.

Though possessing certain aberrant characters, it seems best in the meanwhile to regard the Mosasaurida (= the Pythonomorpha of Cope) as an extinct group of the Lacertilia.

ORDER IV. CROCODILIA.-The last and highest order of the living Reptilia is that of the Crocodilia, including the living Crocodiles, Alligators, and Gavials, and characterised by the following peculiarities:

The body is covered with an outer epidermic exoskeleton composed of horny scales, and an inner dermal exoskeleton consisting of transverse rows of squared bony plates or scutes, which may be confined to the dorsal surface alone, or may exist on the ventral surface as well, and which are disposed on the back of the neck into groups of different form and number in certain species. The bones of the skull and face are firmly united together, and the two halves or rami of the lower jaw are united in front by a suture. There is a single row of teeth, which are implanted in distinct sockets, and hollowed at the base for the germs of the new teeth, by which they are successively pushed out and replaced during the life of the animal. The centra of the dorsal vertebræ in all living Crocodilia are procœlous, or concave in front, but in the extinct forms they may be either amphicoelous (concave at both ends) or opisthocœlous (concave behind).__The vertebral ends of the anterior trunk-ribs are bifurcate. There are two sacral vertebræ. The cervical vertebræ have small ribs (hence the difficulty experienced by the animal in turning quickly); and there are generally false abdominal ribs. produced by the ossification of the tendinous intersections of the recti muscles. There are no clavicles. The heart consists of four completely distinct and separate cavities, two auricles, and two ventricles; the ventricular septum—as in no other Reptiles-being complete. The right and left aorta, however—or, in other words, the pulmonary artery and systemic aorta-are connected together close to their origin by a small aperture (foramen Panizza), so that the two sides of the heart communicate with one another. The aperture of the cloaca is longitudinal, and not transverse as in the Lizards. All the four limbs are present, the anterior ones being pentadactylous, the posterior tetradactylous. All are oviparous.

The chief points by which the Crocodiles are distinguished from their near allies the Lacertilians, are the possession of a partial bony dermal exoskeleton in addition to the ordinary epidermic covering of scales, the lodgment of the teeth in distinct sockets, and the fact that the mixture of venous and arterial blood, which is so characteristic of Reptiles, takes place, not in the heart itself, but in its immediate neighbour