396 JR. S. Ltill — Cranial Musculature in Dinosaurs. 



River Ceratojps canadensis Lambe (1904) in which the supra- 

 orbital horns are powerful, backward ly curved weapons, the 

 squamosals are large, as shown in figure 7. The squamosals 

 are important elements of the frill in all of the later genera, 

 in which the nasal horn is retrogressive aud the supraorbitals 

 all important. 



Though primarily to provide muscular insertion and lever- 

 age, the protective function of the frill was gradually assumed. 

 First along the spine, then along the area of the great veins 

 and arteries of the neck and finally as a complete armor for 



Fig. 7. Ceratops (Monoclonius) canadensis Larnbe ; after Lambe. 



the entire neck. In Torosaurus this final condition was never 

 reached even though the offensive armament was fully equal 

 to that of Triceratops, while in the last mentioned type the 

 ideal frill was attained with its flaring; margin armed with 

 epoccipital bones, giving it a serrated edge which may have 

 aided in aggressive warfare. (Compare figs. 4 and 6.), 



All Iguanodont skulls which the author has seen exhibit a 

 rudimentary crest, with its primary function of attachment 

 for the temporal muscles ; but only in the Ceratopsia has the 

 backward extension for wielding the head and finally for pro- 

 tection of the neck been attained among dinosaurs. (Figs. 8, 9.) 



Part III. Convergencies. 



The distinctively Ceratopsian features are mimicked in a 

 most remarkable manner by other reptiles, notably the turtles 

 and chameleons. 



With the turtles the features in common are the upper and 

 lower beak and the curious false roofing of the skull above the 

 brain case, so that both the turtles and Ceratopsia give the 



