THE CHAMiELEONIDA. 231 



one behind tlie other, and one tooth lies upon the symphysis 

 of the premaxiilEe. 



13. The Chamceleonida. — The Chamseleons are distin- 

 guished from the Kionocrania not only by the negative 

 character of the absence of the columella, which they share 

 with the preceding group, but by a number of very im- 

 portant positive features. Among these I may mention 

 the soft and tuberculated skin, with its changing hues ; the 

 absence of any tympanum; the prehensile tail; and the 

 very peculiarly modified feet. The digits are arranged in 

 bundles of two and three, the manus having the pollex, the 

 index, and the medius, syndactylous and turned inwards ; 

 while, in the foot, it is the hallux and index only which are 

 thus united and turned inwards, the three other toes being 

 similarly connected together by integument, as far as the 

 ungual phalanges, and directed outwards. To these cha- 

 racters may be added the remarkable tongue, callable of 

 protrusion and retraction with almost lightning rapidity. 



The vertebrae of the Chamseleons are similar in their 

 characters to those of the procoelous Kionocrania. The 

 sacrum is composed of only two vertebrae. Only a few of 

 the anterior i-ibs are united with the sternum. A large num- 

 ber of the posterior ribs, as we have already seen to be the 

 case in the Gecko, unite together in the mid-line, and form 

 continuous hoops across the ventral wall of the abdomen. 



But it is in the structtire of the cranium that the 

 CliamcBleonicla depart most completely from the ordinary 

 Lacertilian type. The parietal bone is not moveable 

 upon the occipital, the supra-occi]3ital sending up a median 

 ridge, which unites with the base of a corresponding crest 

 or process extending backwards for a considerable dis- 

 tance from the middle line of the parietal bone. The 

 summit of this sagittal crest is joined by two ciii-ved pro- 

 longations of the squamosal, the three giving the occipital 

 region of the Chamseleon its remarkable casque-like form. 

 The frontal l.^one is comparatively small and single, and 

 the nasals are very narrow, and do not bound any part of 



