CHAPTER IV. 



Scaled Reptiles — Lizards and Chameleons, — Order Squamata ; 

 Suborders Lacertilia and Rhiptoglossa. 



Skull. 



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 chamseleons or serpents, whether they are provided with 

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

 chamaeleons 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 bo 

 taken into consideration. 



Taking their name from the coat of overlapping horny scales 

 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 



LEFT SIDE OF THE VERTEBRA OF 

 A SNAKE. 



over. 



Ribs and 

 Vertebrae. 



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

 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 



