1906.] 



ARTICULATION OF THE VERTEBRATE JAW. 



121 



same time crushing, almost triturating surfaces, indicating that 

 these animals lived upon herbs " (Gadow). 



In the Iguanodon the quadrate is greatly lengthened So. as to 

 place the quadi'ato-mandibular joint below the level of the teeth 

 (text-fig. 45). In this creature the jaw-principle is therefore 

 type 2, only the reptilian form is the mammalian form turned 

 upside down. 



Text-fig. 45. 



Skull of Iffuanodon bernissartensis (teeth not shown in the diagram). 



Text-fiff. 46. 



Diagram of jaws. Type 2 R. 



I shall for convenience refer to this type as type 2 R (text- 

 fig. 46). 



I have not been able as yet to examine any of these skulls 

 closely, and I do not know Avhether the quadrato-mandibular joint 

 would allow a slight amount of horizontal movement to the teeth 

 or not. 



Type 2 R is also to be seen in a slight degree in some Tortoises 

 (text-fig. 47). 



From these investigations I am inclined to believe that animals 



