408 MANUAL OF ZOOLOGY. 



CHAPTER LXIV. 

 LACERTILIA AND CROCODILIA. 



ORDER III. LACERTILIA. The third order of Reptiles is that 

 of the Lacertilia, comprising all those animals which are com- 

 monly known as Lizards, together with some serpentiform ani- 

 mals such as the Blind-worms. The Lacertilia are distinguished 

 by the following characters : 



As a general rule, there are two pairs of well-developed 

 limbs, but there may be only one pair, or all the limbs may be 

 absent. A scapular arch is always present, whatever the con- 

 dition of the limbs may be. An exoskeleton, in the form of 

 horny scales like those of the Snakes, is almost always present. 

 The vertebrae of the dorsal region are procoelous or concave in 

 front, rarely amphiccelous or concave at both ends. There is 

 a single transverse process at each side, and the heads of the 

 ribs are simple and undivided. There is either no sacrum, or 

 the sacral vertebrae do not exceed two in number. The teeth 

 are not lodged in distinct sockets. The eyes are generally 

 furnished with movable eyelids, and are always so in the com- 

 pletely snake-like forms. The heart consists of two auricles 

 and a ventricle, the latter partially divided by an incomplete 

 partition. There is a urinary bladder, and the aperture of the 

 cloaca is transverse. 



As a general rule, the animals included under this order 

 have four well-developed legs (fig. 159), and would therefore 

 be popularly called " Lizards." Some of the Lacertilia, how- 



rig. 159. Iguana. 



ever, have only a single developed pair of limbs, and some have 

 none at all ; thus coming in external appearance closely to re- 

 semble the true Snakes or Ophidians. These serpentiform 



