ADAPTATIONS TO SPECIAL ENDS 143 



a large proportion of their food in the natural condition. The 

 tuatera is the last survivor of a number of extinct reptiles, speci- 

 ally abundant in the Trias, which exhibit a similar type of 

 dentition, but in some instances in a more intensified form. 

 The most remarkable of these are the pavement-toothed tuateras 

 {Hyperodapedon), of which the teeth and jaws are found abund- 

 antly in the Triassic rocks of Europe and India. In place of 

 the double row of lateral upper teeth characteristic of the living 

 tuatera, the pavement-toothed species (Fig. 1 2, B) were furnished 

 with a number of such rows, so that a large portion of the 

 palate was covered with a pavement of bluntly conical teeth, 

 between the outermost and second rows of which worked the 

 knife-like edge of the lower jaw. With the uncertainty existing 

 as to the nature of the diet of the modern tuatera, it would 

 be idle to conjecture what kind of food was consumed by its 

 extinct relative. 



Certain other reptiles had a pavement-like dental armature, 

 developed independently of that of the tuatera. In Endothwdon, 

 for instance, a member of the dicynodont section of the mammal- 

 like anomodonts, the palate was studded with what look like short 

 and closely approximated pegs. More remarkable still are the 

 bean-toothed reptiles (Placodontia), of the Trias, the precise 

 serial position of which is still a matter of uncertainty. These 

 reptiles take their name from the presence of a small number 

 of large flattened teeth covering nearly the whole of the palate, 

 but replaced in the front of the lower jaw by teeth of a chisel- 

 like form. In the typical Placodus these teeth are squared, but 

 in the allied Cyamodus (Fig. 1 2, C) they are more rounded, and 

 much resemble the large Australian beans often mounted as 

 match-boxes. Probably these teeth were used for crushing hard 

 substances, such as shells of crustaceans and molluscs. 



The poison-fangs of snakes form a connecting link between 

 structural modifications connected with food and those for 

 attack and defence, since those weapons are employed both for 

 killing prey and for attacking enemies or for defending their 

 possessors against attack. Although the most specialised of all 

 venomous snakes, such as vipers and rattlesnakes, differ from 

 most harmless species by their depressed and broad heads (such 

 expansion being chiefly due to the great development of the 

 poison-glands), there is really a graddation from the harmless 



