H. S. Lull — Cranial Musculature in Dinosaurs. 387 



Art. XLII. — The Cranial Musculature and the Origin of 

 the Frill in the Ceratopsian Dinosaurs ; by Richard S. 

 Lull. (With Plates I to III.) 



Dollo (1884) in his fifth note on the Dinosaurians of 

 Bernissart has discussed the muscles of mastication of certain 

 dinosaurs in comparison with those of a rodent, a crocodile, 

 and a chameleon. This work has- suggested to the writer a 

 further study of the musculature of the skull, especially in the 

 Ceratopsia, with a view of gaining an insight, if possible, into 

 the origin of the peculiar defensive cranial armor of this 

 remarkable group. 



These studies are based more particularly on the type skulls 

 of Triceratops serratus and T. prorsus Marsh which are pre- 

 served in the Peabody Museum at Yale, supplemented by an 

 admirable palate, referred to the former species, in the Ameri- 

 can Museum of Natural History. The chief basis for compar- 

 ative study has been the modern chameleon, which, as the 

 author will show, exhibits some very remarkable points of 

 convergence in structure toward the Ceratopsia. 



Part I. Musculature. 

 Muscles of mastication. 



The Iguanodont dinosaurs differed from all other reptiles in 

 their method of feeding in that they were herbivores which 

 masticated their food, thus requiring a development of mus- 

 cles, especially the temporal, rare among reptiles. Chameleons, 

 though insectivorous, and having the tongue for prehension, 

 use the teeth, not for holding, but for chewing the firm- 

 bodied Orthoptera and Lepidoptera which constitute their 

 food. There is thus an analogy between the chameleons and 

 the Iguanodontia in contrast to the carnivorous dinosaurs 

 which, like the crocodiles, used the jaws for holding and tear- 

 ing the prey rather than for mastication. The chameleons 

 have enormous temporals, while in the crocodiles, as Dollo 

 (1884) has shown, the temporals are relatively small and the 

 pterygoid muscles, which in chameleons are feeble, are corre- 

 spondingly large. In other words, the temporals are the larger 

 in masticating forms ; the pterygoids where the jaw function is 

 largely one of resistance and, correlated with the development 

 of the temporals, there is a corresponding development of the 

 coronoid process of the jaw. In Triceratops, and other Cera- 

 topsia, the jaw is powerful, articulated to a rigid suspensorium 

 consisting of the quadrate, quadrato-jugal and the strong over- 

 lying jugal. The two dentaries meet in symphysis and their 

 union is further strengthened by the massive ju'edentary bone 



