"BEAKED LIZARDS." 15 



all its contemporaries. The evidence on which 

 this decision is based is of too technical a char- 

 acter for discussion here : we need only say that 

 it rests upon the structure of the skeleton, and 

 of certain internal characters related to the 

 organs of generation. 



Of the skeletal structures which appear again 

 in other groups, sometimes strangely modified, 

 we may mention one or two of the more im- 

 portant. The ribs, for example, in the Tuatera 

 are remarkable for the presence of curious hook- 

 like processes which project backwards from the 

 middle of the upper portion of each rib, to 

 overlap the rib next behind it. These " uncinate " 

 processes occur elsewhere only among the Croco- 

 diles and the birds. Behind the breastbone are 

 found numerous rod-like bones embedded in the 

 muscles of the belly. These are commonly known 

 as the " abdominal ribs " ; they occur again in the 

 Crocodiles and the ancient " Labyrinthodonts " 

 and " fish-lizards," and it is probable that from 

 the fusion of similar bones the singular shield 

 on the belly of the Tortoise has been derived. 

 The teeth are quite remarkable. Numerous and 

 irregular in size, they occur not only along the 

 edges of the jaws, but also on the bones of the 

 palate. These teeth are not renewed when worn 

 out as in most other reptiles, but fusing with the 

 edges of the jaws gradually wear away till, in 

 very old individuals, the jaws become toothless. 

 It is on this account that the name beaked 

 lizards has been bestowed. Large males attain 

 a length of about two feet and a half. Both 

 sexes are alike save only in that the males have 



