CHAPTER IV. 



Scaled Reptiles — Lizards and Chameleons, — Order Squamata ; 

 Suborders Lacertilia and Rhiptoglossa. 



Although in popular language the term lizard is applied to any four-legged reptile, 



exclusive of turtles and crocodiles, in scientific usage it is more convenient to restrict 



it to those members of the great group of scaled reptiles which do not come under 



the designation of either chamaeleons or serpents, whether they are provided with 



legs, or whether they lack those useful appendages. Formerly, indeed, lizards and 



chamasleons were regarded as constituting an order by themselves quite apart from 



serpents, but the two groups are now known to be so intimately connected as to 



render any such division inadmissible ; and they are accordingly here placed in a 



single order, known as scaled reptiles, or, technically, Squamata. Structurally, this 



ordinal group differs very widely indeed from any of those hitherto treated, and as 



it is essential to gain a correct idea of such structural differences, they may first be 



taken into consideration. 



Taking their name from the coat of overlapping: horny scales 

 Skull. . & . ri ^ . 



with which they are generally invested, the scaled reptiles are 



primarily distinguished from all the foregoing groups by the circumstance that the 

 quadrate-bone is more or less movably articulated to the skull, and has its lower 



end projecting freely therefrom, instead of being immov- 

 ably wedged in among the other bones. To this primary 

 point of distinction it may be added that the lower 

 temporal arch of the skull is wanting, so that there is 

 no bony bar connecting the lower end of the quadrate- 

 bone with the upper jaw, as there is in the crocodiles ; 

 the absence of this bar being well shown in the figure of 

 a lizard's skeleton. Then, again, the palate, instead of 

 being more or less completely roofed over by bone, is 

 largely open, its bones taking the form of long bars. 

 In some lizards, as in the one of which the skeleton 

 is figured, the upper surface of the skull is covered 

 by bone, so that the temporal fossae are roofed 

 over. 

 Ribs and Another important feature of the order is to be found in the 



Vertebrae, circumstance that the ribs in the region of the back are single-headed, 

 and are articulated to the backbone by means of a facet (d) situated on the body 

 of each vertebra. This feature at once distinguishes the order from the crocodiles 

 and dinosaurs, in which the ribs are two-headed, and in the back articulate to a 



LEFT SIDE OF THE VERTEBRA OF 

 A SNAKE. 



