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Show 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 quadrato-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 Iguanodon bernissartensis (teeth not shown in the diagram). Text-fig. 46. Diagram of jaws. T}'pe 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 whether 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 a m inclined to believe that animals |