P.EPTILIA. 271 



j^ellow vipei-s, neither is poisonous, nor even in the slightest degree noxious, 

 although of quite terrific appearance and demeanor Avlien enraged. 



An exceedingly interesting illustration of the special provision Avhich nature 

 sometimes makes for particular cases is seen in the African genus Deirodon. 

 To this has been imputed the instinct of living almost entirely on the eggs of 

 birds, and its whole organization fits it expressly for this end. The mouth is 

 entirely without teeth, at least in the adult, so that nothing interferes to prevent 

 the ready entrance of an egg into the open jaw, and there is no liability of its 

 losing any of the contents by a premature breakage. The inferior spinous 

 processes of the seven or eight inferior cervical vertebme project with the 

 oesophagus, where they are cappe<l by a layer of hard cement and made to 

 resemble long sharp teeth. The descending egixs press against these teeth and 

 are sawed open longitudinally, and then, crushe;! by the contractions of the 

 gullet, are carried into the stomach, where the shell is probabl}^ dissolved by 

 the gastric juice and digested with the contents. 



Order 3, Sauria. 



The third order of Reptiles, the Sauria or Lizards, embraces species of 

 very diversified character, especially when we take into consideration certain 

 fossil forms. Their size, too, varies from that of a few inches to 30 feet, as 

 in some recent crocodiles. This magnitude, however, is far exceeded by 

 certain extinct species. The body is generally cylindrical, sometimes 

 slightly depressed, elongated, and with a skin provided with scales (p/iotides), 

 granulations, or bony plates. The photides they share with the Ophidia, 

 and the two orders are thus distinguishable from Batrachia, only a single 

 family of which, the CoeclUadci'. has minute cycloidal, fish-like scales, nearly 

 concealed in the folds of the skin. By the four feet they are distinguishable 

 from serpents, although, in a few instances, these members are partly or 

 entirely wanting externally. The feet, when present, are usually provided 

 with true claAvs, supported on the terminal phalanges. The tail is developed 

 to a greater or less extent, while the cloaca presents itself externally as a 

 transverse slit. The almost universal presence of an external meatus 

 auditorius, or at least of a tympanum (excepting in Acontias, Typhline, and 

 a few others), distinguishes the Sauria from the Ophidia ; as also the presence 

 of a sternum, connected Avith the vertebral column by movable ribs, and 

 the greater immobility of the bones of the head. The rami of the lower 

 jaw are firmly united together, and the entire skidl is compact. Few Sauria 

 are without movable eyelids, altliough these are occasionally very rudimentary. 

 The teeth are variously disposed, as will be seen Avhen we come to consider the 

 different families. Many species are only known to us in a fossil state, these 

 generally of great size. 



Fam. 1. ScinddcB. This family, standing at the foot of the great order 

 of Saurians, is characterized, in the first place, by the possession of large 

 plates on the top of the head, which are in contjxct along the edges ; and by 

 their angular and regular shapes, closely resemble the homologous plates of 



475 



