Brain and In the higher Reptilia the cerebrum attains a comparatively larger size than in the lower forms, while the cerebellum also attains a relatively higher de velopment as we proceed upward. The cere bellum has no lateral lobes nor pons, while the corpora bigemina and thalami are of large size. The senses are developed in tolerable perfection. The nasal cavities are of large size and open into the mouth through either the anterior or posterior part of the palate. In the Crocodilia the hinder nostrils open very far back in the month, enabling these animals to hold their prey under water in their mouths, and so to drown it, while their own respiration is carried on un impeded through the nostrils. The eyes are usually of small size, and exhibit variations in structure and in the disposition of the protec tive coverings. Thus in snakes the eye-ball in front is covered by a transparent lid, formed by a layer of the skin, which is attached to a circle of surrounding scales, and is shed periodically, with the outer skin. In snakes the pupil of the i eye is round. In the lizards movable and ordi nary eyelids exist, while the turtles possess a nictitating membrane. In lizards and snakes the sclerotic coat of the eye is strengthened by a circle of bony plates, such as also occur in sev eral extinct reptilian forms and in birds. In the chameleons the single eyelid is formed by the united lids, and through an opening in this circular lid the rays of light enter the pupil of the eye within. The tympanum of the ear is imperfectly developed in Ophidia, and no eusta chian tube exists. In lizards the tympanic ap paratus is better developed, while in chelonians the tympanic cavity is large and complicated, and a rudimentary cochlea exists. The Croco dilia possess a movable valve, by means of which the tympanic canal of each ear can be dosed at will; and most of the structures found in the ear of higher Vertebrate are represented in greater or less structural detail and perfec tion.
The kidneys are generally placed far back and deep within the pelvic cavity. In the serpents, however, the kidneys are situated anteriorly, and are unsymmetrically placed, the right being higher up and in advance of the left kidney; they also are divided into small lobes. No urinary bladder exists, and the urine of the lizards is fluid; that of the ser pents resemble the excrement of birds in being pasty and crystalline. In Crocodilia the testes are elongated, and placed in front of the kid neys. The penis in Crocodilia is single, grooved and contained within a special cloacal fold; in Ophidia two lateral penes exist, and these are hollow and evertible; a double penis exists in lizards, while that of turtles is single.
The eggs are generally of relatively large size, and provided with a thick parchment-like shell and a large yolk. In many instances the eggs may be deposited in sand and hatched by the sun's heat.
With regard to the distribu tion in space of reptiles, the warm or tropical regions of the earth contain these animals not only in greatest number, but in most typical form and variety. During winter or in the colder seasons of the year, most reptiles hiber nate and many desert, species also pass into a summer sleep. Reptiles are varied in their habits, most of them being terrestrial, but many arboreal and some, including the great ma jority of the turtles, are aquatic. While most are strictly carnivorous or insectivorous, some subsist on a general diet and a few are purely vegetarian. Many of the extinct forms fed exclusively on fishes. Reptiles exhibit many interesting habits, but, owing to a popular prej udice against them and the tax on the patience of the observer resulting from their inactivity and secretiveness, they have been comparatively little studied.
Classification.— Because of certain resem blances in form and manners, all of the early zoologists, to and including Cuvier, classed the Reptilia and Amphibia together, and it was only when embryological data began to play an important part in taxonotny that their dis similarity was perceived. Milne-Edwards and
his contemporaries toward the middle of the 19th century were the first to recognize this in a scheme of classification. In when zoologists were still working under the fresh stimulus of the publication of the 'Origin of Species,' Huxley, Haeckel and Cope almost simultaneously perceived much more clearly than had any of their predecessors the close relationship and probable community of descent of birds and reptiles. Reptilian life played a much more important role in past ages of the earth than now, that it is not surprising that we must turn to paleontologists for nearly all of the recent advances in the classification of the groups. The scheme and nomenclature mainly followed in this work is that elaborated by Gadow in Vol. VIII of the 'Cambridge Natural History.' CLASS REpritia.Class REpritia.
Subclass Proreptilia.
Subclass Prosauria. Orders: Microsauri, Prosauri (Rhynchocephalia, etc.).
Subclass Theromorpha. Orders: Pareia sauri, Theriodontia, Placodontia, Anomodontia.
Subclass Chelonia (Turtles). Orders: Ath eca, Thecophora.
Subclass Dinosauria (Dinosaurs). Orders: Sauropoda, Theropoda, Orthopoda, Ceratopsia.
Subclass Crocodilia (Crocodilians). Or ders: Pseudosuchia, Parasuchia, Eusuchia.
Subclass Plesiosauria. Orders: Nothosauri, Plesiosauri.
Subclass Ichthyosauria. Orders: Ichthyo sauri (Fish-lizards).
Subclass Pterosauma (Flying Reptiles). Or der: Pterosauri (Pterodactyls).
Subclags Pythonomorpha, Orders: Dolicho satiri, Mosasauri.
Subclass Sauria. Orders: Lacetilia (Liz ards); Ophidia (Serpents).
A more elaborate scheme, but one which more correctly expresses the natural relation ships of the orders, has been developed by Cope, Baur and Osborn.
The vast majority of reptilian types have become extinct Only four orders are repre sented in our modern fauna, and one of these, the Rhynchocephalia, by only a single species, the New Zealand tuatera. The Crocodilia have greatly declined in variety of forms since the close of the Mesozoic Age. The Pythono morpha have become extinct, but lizards and snakes are represented in the saurian orders by a great number of species and are the only dominant reptilian types. Reptiles flourished especially during the Mesozoic Age, to which four of the most remarkable groups were con fined, the great marine reptiles (Plesiosaur-la and Ichthyosauria), the huge and often remark ably modified terrestrial Dinosauria and the equally wonderful flying Pterosauria. This epoch, when the seas were shrinking and dry land increasing in extent, but when the atmos phere was heavy with moisture and carbonic acid gas, unfitted for the respiration of high types of life, was well suited for the develop ment of the sluggish reptiles; and they were dominant on land and sea, replacing on the one hand the amphibians and on the other the primi tive types of fishes of earlier ages. With the close of the Age of Reptiles and the advent of the Eocene Period, mammals quickly rose to full dominance on the land and many orders of reptiles, having played their parts in the evolution of life, disappeared forever. Reptiles sprang from the stegocephalian Amphibin. From some group of the Theromorpha (of the synapsidan series) mammals are supposed to have come; while birds took their origin from the diapsi4n line, probably in common with some primitive dinosaurian.
Consult, besides the numerous articles in this work on special orders and kinds of rep tiles, the following: Cope, (The Crocodilians, Lizards and Snakes of North America,> Re port of United States National Museum (Wash ington 1900) ; Holbrook, (North American Herpetology) (Philadelphia 1842) ; Gadow, 'Amphibia and Reptiles) (New York 1901); Boulenger, 'Catalogue of the Reptiles in the British Museum) (London 1889-96) ; Osborn, (The Reptilian Subclasses Diapsida and Synapsida,> Memoirs American Museum of Natural History (New York 1903); Woodward, (Vertebrate Paheontology)