198 THE ANATOMY OF VERTEBKATED ANIMALS. 



one another. And, in the hindermost caudals, the spinous 

 processes and the chevron-bones disappear. 



There were strong" ribs, but nothing is knoAvn with cer- 

 tainty of the sternum, limb-arches, or other bones. 



The very complete specimens of the skull that have been 

 discovered prove that its structure was very similar to that of 

 the Old World Monitors in the large size of the nasal aper- 

 tures, and the fusion of the nasals into a narrow bone. 13ut 

 sharp recurved teeth are anchylosed by their bases, not only 

 to the premaxillary, maxillarj^, and dentary bones, but also to 

 the pterygoid bones ; and these pterygoid bones are unlike 

 those of other Lacertilia^ not only in form, but because they 

 articulate together in the middle line for a considerable dis- 

 tance behind the posterior nasal aperture. 



12. The Ampliishoenoida. — These lizards have completely 

 snake-like bodies ; one genus of the group ( Chirotes) has a 

 pair of small pectoral members, but the rest are apodal. The 

 integument of the body is not scaly, but its surface is divided 

 into small rectangular arose arranged in transverse rows. The 

 tail is exceedingly short, so that the v^ent is close to the end 

 of the body. 



The numerous procoelous vertebrre have less elliptical 

 articular faces than those of the typical Lacertilia. There is 

 no sacrum, and all the precaudal vertebrae, except the one or 

 two of the most anterior, have ribs. The representatives of 

 the chevron-bones in the tail are firmly united with the centra 

 of the vertebrae. The vertebrae have no zygantrum nor zygo- 

 sphene. Ampliisboena has no sternum. Chirotes has a ster- 

 num, but it is not united with the ribs. 



The skull, unlike that of Lacertilia in general, develops no 

 interorbital septum. In this respect, and in the complete 

 closure of its anterolateral walls by bone, it resembles the 

 Ophidian cranium. There is no columella. Post-frontals are 

 absent, and the squamosal is very small. The quadrate bone 

 is small, and inclined not only downward, but forward, in a 

 manner unknown in other Lacertilia. The two rami of the 

 mandible are firmly united by suture. 



In A.mphisbmna the premaxillge bear two rows of teeth, 

 one behind the other, and one tootli lies upon the symphysis 

 of the premaxillai. 



13. The Chawceleonida. — The Chamasleons are distin- 

 guished from the I^ionocrarda not only by the negative 



