Families of lizards 703 



fragilis is not blind or poisonous, as popularly asserted ; the tail breaks 

 readily ; the young are hatched within the mother. 



The poisonous Mexican and Arizona lizards {Heloderma horridum 

 and H. suspectum) are over a foot in length, and are covered with 

 bead-like scales. 



The Varanida? are large carnivorous forms, most at home in Africa, 

 but represented also in Asia and Australia. The Monitor of the Nile, 

 Vafanus niloticus, 5 or 6 ft. long, destroys eggs and young of Crocodiles. 



The Amphisb^enidae are degenerate subterranean lizards, without 

 Umbs, with rudimentary girdles, with no sternum, with small covered 

 eyes, with hardly any scales. 



The Lacertidae are Old World pleurodont lizards, such as Pseudopus 

 (Europe and S. Asia) and Lacerta viridis, the green lizard of Jersey 

 and S. Europe. 



The Chamaeleons (Chamaeleontidee) are very divergent lizards, 

 mostly African. There is one genus, Chamceleo. The head and the 

 body are compressed ; the scales are minute ; the eyes are very large 

 and separately movable, with circular eyelids pierced by a hole ; the 

 tympanum is hidden ; the tongue is club-shaped and viscid ; the 

 digits are divided into two sets, and well adapted for prehension ; the 

 tail is prehensile ; the power of colour-change is remarkably developed. 



The Chameleons exhibit numerous anatomical peculiarities. As in 

 the Amphisbaenas, there is no epipterygoid. The pterygoid does not 

 directly articulate with the quadrate, which is ankylosed to the adjacent 

 bones of the skull. 



Fourth Order : Ophidia. Serpents or Snakes 



The elongated limbless form of snakes seems at first sight 

 almost enough to define this order from other Reptiles, but 

 it must be carefully noticed that there are limbless Lizards, 

 limbless Amphibians, and limbless Fishes, which resemble 

 snakes in shape though they are very different in internal 

 structure. For the external shape is in great part an 

 adaptation to the mode of life, to the habit of creeping 

 through crevices or among obstacles. But the limblessness 

 of serpents is not a merely superficial abortion ; there is no 

 pectoral girdle nor sternum, and never more than a hint of 

 a pelvis. 



General Characters. — The skin is covered with scales, 

 and the outermost epidermal layer is periodically shed in 

 a continuous slough. 



There are never any hints of anterior appendages, girdles, 

 sternum, or episternum ; but in pythons, boas, and a few 

 others there are rudiments of a pelvis, and even small clazved 

 structures which represent hind-legs. 



